PHOENIX IS FLYING TO MARS
On Saturday, August 4, 2007 from Cape Canaveral, Florida, a Boeing Delta II rocket launched the Phoenix mission toward the planet Mars. The Phoenix mission is the first chosen for NASA's Scout program, an initiative for smaller, lower-cost, competed spacecraft. The Phoenix mission is named for the resilient mythological bird that was reborn from the ashes of its former life. This is partly because pieces of the mission were created for previous missions. The lander itself was intended for use by 2001's Mars Surveyor lander prior to its cancellation. It also carries a complex suite of instruments that are improved variations of those that flew on the lost Mars Polar Lander.
In the continuing pursuit of water on Mars, the poles are a good place to probe, as water ice is found there. Phoenix will land on the icy northern pole of Mars between 65 and 75 degrees-north latitude. During the course of the 150 sol (Martian day) mission, Phoenix will deploy its robotic arm and dig trenches up to half a meter (1.6 feet) into the layers of water ice. These layers, thought to be affected by seasonal climate changes, could contain organic compounds that are necessary for life.
To analyze soil samples collected by the robotic arm, Phoenix will carry an "oven" and a "portable laboratory." Selected samples will be heated to release volatiles that can be examined for their chemical composition and other characteristics.
Imaging technology inherited from both the Pathfinder and Mars Exploration Rover missions will also be implemented in Phoenix's stereo camera, located on its 2-meter (6.6-foot) mast. The camera's two "eyes" will reveal a high-resolution perspective of the landing site's geology, and will also provide range maps that will enable the team to choose ideal digging locations. Multi-spectral capability will enable the identification of local minerals.
To update our understanding of martian atmospheric processes, Phoenix will also scan the martian atmosphere up to 20 kilometers (12.4 miles) in altitude, obtaining data about the formation, duration and movement of clouds, fog, and dust plumes. It will also carry temperature and pressure sensors.
For more information on the Phoenix mission, visit: http://phoenix.lpl.arizona.edu/
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THE SKY THIS WEEK
Here are some observing highlights for the week. These events are given from the perspective of observers in the northern hemisphere. No offence to southern-hemisphere folks, it's just because of where I live.
Oct 1, 1:00 to 4:00 AM EDT - The orange-colored planet Mars is less than 7' (7 arcminutes) from 1 Geminorum. (yellow star, spectral type G7III) sometimes called Propus ("forward foot," of Castor, that is) , though that name is mostly used with Eta Geminorum. (1 Geminorum specifics: RA 06hrs 04 07.2min, Dec +23 degrees 15 48, distance 2,800 ly, visual brightness 0.82 magnitude. Mars is shining brighter at -0.1 magnitude).
Oct 3, 6:06 am EDT - Last-quarter Moon
Oct 3 and 4, Early Morning - Mars is less than 1 degree south of the open star cluster M35 (Messier catalog number 35) in Gemini (M35 specifics: RA 06hrs 08.9min, Dec +24 degrees 20 min, distance 2,800 ly, visual brightness 5.3 magnitude).
Oct 5, Before Dawn - Moon is roughly 1 degree north of M44, the Beehive Cluster, also called Praesepe (Latin for "manger"). in the constellation Cancer (M44 specifics: RA 08hrs 40.1min; Dec +19 degrees 59 minutes, distance 577 ly, Visual Brightness 3.7 magnitude.
Oct 7, Early Dawn - A thin crescent Moon is joined by the planets Venus and Saturn and the star Regulus. Western Europe and Morocco will see the Moon occult Regulus. The rest of Europe and Middle East will see it after sunrise, if possible.
Terminology Notes:
arcminute, minute of arc (MOA) - equal to one sixtieth (1/60) of one degree. The symbol is the prime or apostrophe ('), sometimes abbreviated as arcmin or amin.
Degree - one three hundred sixtieth (1/360) of a circle
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THIS WEEK IN HISTORY
- Astronomy and Science Events -
October 3, 1264 – A comet said to predict death of Pope Urban IV was last seen
October 2, 1608 – The prototype of the modern reflecting telescope was completed by Jan Lippershey
October 4, 1675 - Christian Huygens patented pocket watch
October 1, 1847 - Maria Mitchell discovered a non-naked-eye comet
October 1, 1888 - National Geographic magazine was first published
October 4, 1957 - U.S.S.R. launched Sputnik I, the first artificial Earth satellite
October 1, 1958 – Management of the Vanguard Project was transferred from the Naval Research Laboratory to NASA
October 1, 1990 - Meteor exploded above the Pacific Ocean
October 1, 1962 - US National Radio Astronomy Observatory got a 300' (91m) radio telescope
- Events Noted For Fun -
October 1, 1746 - Bonnie Prince Charlie fled to France (see below)
October 3, 1916 - James Alfred Wight Herriot, veterinarian/novelist
October 1, 1935 – Actress and singer Julie Andrews was born in England
October 1, 1939 - Churchill called the Soviets a "riddle wrapped in a mystery inside an enigma"
October 1, 1942 - Little Golden Books (children books) begins publishing
October 3, 1955 – the children’s television program "Captain Kangaroo" premiered on CBS-TV
October 1, 1971 - Walt Disney World in Orlando, Florida opens
October 1, 1982 - EPCOT Center opens in Orlando, Florida
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BONNIE PRINCE CHARLIE AND THE SKYE BOAT SONG
Charles Edward Stuart (Bonnie Prince Charlie), the Young Pretender, led the Jacobite uprising, but was defeated by the Duke of Cumberland on Scotland’s Culloden Moor in 1746. Aided by a Jacobite heroine named Flora MacDonald, who disguised him as her serving maid, Charles escaped from Uist to the island of Skye. He was later taken by a French vessel to Morlaix on the coast of Bretagne. Unlike the hope expressed in the song, and despite various political and religious maneuvers that took place over the following forty years, Charles did not return to take up the fight again. He died in Rome in 1788.
The words of the song were written in 1884 by business man, philanthropist, and song writer Sir Harold Boulton, Bart. (baronet) who lived from 1859 to 1935. The first half of the tune (the chorus) is said to be an old sea shanty (in this case, a Gaelic rowing song called "Cuachag nan Craobh," or "The Cuckoo in the Grove"); the second half of the tune (the verse portion) is traditionally attributed to Miss Annie MacLeod (Lady Wilson). The song was not considered a traditional Scottish favorite until recent times. It is sometimes sung as a lullaby in a slow rocking time, or danced as a waltz.
The Skye Boat Song
Chorus:
Speed bonnie boat, like a bird on the wing,
Onward, the sailors cry
Carry the lad that's born to be king
Over the sea to Skye
Loud the winds howl, loud the waves roar,
Thunder clouds rend the air;
Baffled our foe's stand on the shore
Follow they will not dare
(Chorus)
Though the waves leap, soft shall ye sleep
Ocean's a royal bed
Rocked in the deep, Flora will keep
Watch by your weary head
(Chorus)
Many's the lad fought on that day
Well the claymore could wield
When the night came, silently lay
Dead on Culloden's field
(Chorus)
Burned are our homes, exile and death
Scatter the loyal men
Yet, e'er the sword cool in the sheath,
Charlie will come again.
(Chorus)
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To review the history, the text, or to listen to the melody, check out this page from the Scottish Folk Music section of “Contemplations from the Marianas Trench - Music and Deep Thoughts” - http://www.contemplator.com/scotland/skyboat.html
To see a GIF image file of the score of the song, or to download an ABC file of the score, visit this page of “The Session” - http://www.thesession.org/tunes/display/3690
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Saturday, September 29, 2007
Sunday, September 23, 2007
Happy Equinox!
Earth's most recent equinox occurred today, September 24, at 9:51 UT (5:51 am EDT). Equinox is the time when the plane sun (the ecliptic) crosses the earth’s equator (also known as the celestial equator). At this time night and day are approximately equal in length. The word equinox literally means “equal night,” suggesting the thought that the length of night and day are equal. Equinox occurs twice each year, or twice in each orbit of the earth. The approximate dates each year are March 21 and September 22. For the hemisphere into which the sun crosses, it is the beginning of spring (the spring or vernal equinox), and for the hemisphere out of which the sun leaves, it is the beginning of autumn, or fall (the autumnal equinox). In the northern hemisphere this year’s autumnal equinox occurred today.
Many people still think that earth’s seasons are caused by changes in the distance of earth around the sun over the course of the year. This is just not the case. While it is true that the orbit of earth is elliptical and that its distance from the sun changes during the year, the difference between the distances is not significant enough to make a difference. For example, this year earth’s closest point to the sun, or earth’s “perihelion,” was January 3 at about 20:00 UT, when the earth-sun distance was 147,093,602 km, and earth’s farthest point from the sun, or earth’s “aphelion,” was July 7 at about 00:00 UT, when the earth-sun distance was 152,097,053 km. The difference between these two is 5,003,451 km, or a 3.3 percent difference.
The phenomenon of seasons (spring, summer, autumn, and winter) is the result of two effects: the tilt of earth’s axis of rotation and the amount of sunlight that reaches earth’s northern and southern hemispheres each day. The earth is tilted about 23.5 degrees (23 degrees 26 minutes) relative to the earth’s orbit around the sun. Most of the time, this tilt causes one hemisphere to experience more daylight than the other. This different can make one hemisphere warmer or colder because of the amount of heat, or thermal energy, that the surface below absorbs and hangs on to during the night that follows.
Aside from the change in temperature, the change in the amount of daily sunlight affects all plant life. Plants use chlorophyll, the green stuff, to capture the sun’s energy and use it, along with carbon dioxide, water and organic nutrients from the soil to make the sugars and starches they use as food. This process is otherwise known as photosynthesis. Over the course of the four seasons the amount of daily sunlight gradually increases and then gradually decreases. When the amount of sunlight is too little for the plant to perform photosynthesis, the plant shuts down its photosynthesis factory and begins to live on its stored food. Many plants even get rid of their solar collectors, or their leaves. When the amount of daily sunlight begins to grow again, the plants put out their solar collectors and crank up the factory. For many people this annual cycle of the leaves is more significant than the rise and fall of temperature.
Ok, enough of the details. You get the idea. A very happy equinox to all!
Earth's most recent equinox occurred today, September 24, at 9:51 UT (5:51 am EDT). Equinox is the time when the plane sun (the ecliptic) crosses the earth’s equator (also known as the celestial equator). At this time night and day are approximately equal in length. The word equinox literally means “equal night,” suggesting the thought that the length of night and day are equal. Equinox occurs twice each year, or twice in each orbit of the earth. The approximate dates each year are March 21 and September 22. For the hemisphere into which the sun crosses, it is the beginning of spring (the spring or vernal equinox), and for the hemisphere out of which the sun leaves, it is the beginning of autumn, or fall (the autumnal equinox). In the northern hemisphere this year’s autumnal equinox occurred today.
Many people still think that earth’s seasons are caused by changes in the distance of earth around the sun over the course of the year. This is just not the case. While it is true that the orbit of earth is elliptical and that its distance from the sun changes during the year, the difference between the distances is not significant enough to make a difference. For example, this year earth’s closest point to the sun, or earth’s “perihelion,” was January 3 at about 20:00 UT, when the earth-sun distance was 147,093,602 km, and earth’s farthest point from the sun, or earth’s “aphelion,” was July 7 at about 00:00 UT, when the earth-sun distance was 152,097,053 km. The difference between these two is 5,003,451 km, or a 3.3 percent difference.
The phenomenon of seasons (spring, summer, autumn, and winter) is the result of two effects: the tilt of earth’s axis of rotation and the amount of sunlight that reaches earth’s northern and southern hemispheres each day. The earth is tilted about 23.5 degrees (23 degrees 26 minutes) relative to the earth’s orbit around the sun. Most of the time, this tilt causes one hemisphere to experience more daylight than the other. This different can make one hemisphere warmer or colder because of the amount of heat, or thermal energy, that the surface below absorbs and hangs on to during the night that follows.
Aside from the change in temperature, the change in the amount of daily sunlight affects all plant life. Plants use chlorophyll, the green stuff, to capture the sun’s energy and use it, along with carbon dioxide, water and organic nutrients from the soil to make the sugars and starches they use as food. This process is otherwise known as photosynthesis. Over the course of the four seasons the amount of daily sunlight gradually increases and then gradually decreases. When the amount of sunlight is too little for the plant to perform photosynthesis, the plant shuts down its photosynthesis factory and begins to live on its stored food. Many plants even get rid of their solar collectors, or their leaves. When the amount of daily sunlight begins to grow again, the plants put out their solar collectors and crank up the factory. For many people this annual cycle of the leaves is more significant than the rise and fall of temperature.
Ok, enough of the details. You get the idea. A very happy equinox to all!
Saturday, September 22, 2007
Journey to the Dawn of the Solar System
This week should see the launch of NASA’s mission to very the dawn of our solar system. It’s name? Appropriately enough, Dawn. The goals of the Dawn mission are to understand what it was like at the beginning of the solar system, and to understand how the solar system formed. The mission will do this by making an up-close study of “protoplanets.” According to the current theory of planetary formation, protoplanets are the early stage in the development of planets, condensing out of gas clouds surrounding a young star.
The Dawn mission will carefully examine two of the largest protoplanets that remain. They are Ceres, which has recently been classified as a dwarf planet, and the asteroid Vesta. Both of these bodies orbit the sun with many other smaller bodies in the large area between Mars and Jupiter that is called the asteroid belt. These protoplanets, or baby planets, were interrupted in their process of becoming something larger, by the formation of Jupiter, with its tremendous gravity. Ceres, Vesta, and the rest of the bodies in the asteroid belt have followed different evolutionary paths because of the many different processes that operated during the first few million years of the solar system.
The biggest question that the Dawn mission addresses is the role of size and water in determining the evolution of the planets. Ceres and Vesta are the right two bodies with which to address this question, as they are the most massive of the protoplanets, baby planets whose growth was interrupted by the formation of Jupiter. Ceres is very primitive and wet while Vesta is evolved and dry. The instrumentation to be flown is complete, flight- proven and similar to that used for Mercury, Mars, the Moon, Eros and comets. The science team consists of leading experts in the investigation of the rocky and icy planets using proven measurement and analysis techniques.
Dawn has the potential for making many discoveries that could change the way scientists think. For example, Ceres may have active hydrological (water-based) processes leading to seasonal polar caps of water frost, altering our understanding of the interior of these bodies. Vesta may have rocks more strongly magnetized than on Mars, altering our ideas of how and when dynamos arise with important lessons for Mars, Earth and Mercury. Ceres may have a thin, permanent atmosphere distinguishing it from the other minor planets. These are just examples, but even more unexpected discoveries may be made along the journey.
The Dawn mission has three principal scientific drivers. First, to capture the earliest moments in the origin of the solar system, enabling us to understand the conditions under which these bodies formed. Second, to determine the nature of the building blocks from which the terrestrial planets formed and thereby improve our understanding of this formation. Finally, to contrast the formation and evolution of two small bodies that followed very different evolutionary paths, so that we can understand what controls that evolution.
And continuing the theme of “threes,” the Dawn mission accomplishes three goals for NASA. First, the gathered data will provide some context for interpreting the growing observations of extra solar-planetary systems. Second, the mission will provide information on the role of size and water in planetary evolution and form a bridge between the exploration of the rocky inner solar system and the icy outer solar system. Finally, the mission completes the first order exploration of the inner solar system, addressing NASA's goal of understanding the origin and evolution of the solar system and complements NASA’s ongoing investigations of Mercury, Earth and Mars.
Background on Ceres and Vesta
Ceres is the largest asteroid (designated 1 Ceres), the first to be discovered and was recently designated as a dwarf planet. Ceres is named after the Roman goddess of agriculture. It was discovered by Giuseppe Piazzi of the Palermo Observatory on Jan. 1, 1801. Additional observations by Piazzi were cut short due to illness. Carl Friedrich Gauss, at the age of 24, was able to solve a system of 17 linear equations to determine Ceres' orbit and to allow it to be rediscovered, a remarkable feat for this time. As a result within one year of its initial discovery, both Heinrich Olbers and Franz von Zach were able to relocate Ceres. It revolves around the Sun in 4.6 terrestrial years and has a diameter estimated at about 960 km (600 miles).
Vesta, the brightest asteroid (designated 4 Vesta), is named for the ancient Roman goddess of the hearth and is the only asteroid ever visible with the naked eye. Found on March 29, 1807, by Heinrich Olbers, it was the fourth minor planet to be discovered. It is the second most massive and the third largest asteroid. It revolves around the Sun in 3.6 terrestrial years and has an average diameter of about 520 km (320 miles). Its surface composition is basaltic.
Dawn Mission Timeline
At of this writing, the launch is scheduled for Wednesday, September 26, 2007, with a launch window of 7:25 a.m. - 7:54 a.m. EDT. The eight-year Dawn mission timeline is as follows:
September 2007, Launch – Dawn will launch from … and goes into a solar orbit, moving out to the orbit of the planet Mars.
March 2009, Mars gravity assist – Dawn will make a close approach to Mars and steal a bit of inertia from the planet, making the spacecraft go fast enough to move farther out, toward the main asteroid belt.
September 2011, Arrival at Vesta – Dawn will go into orbit around Vesta and will study the body for approximately seven months.
April 2012, Depart Vesta – Dawn will gradually spiral away from Vesta and begin to journey farther out toward Ceres.
February 2015, Arrival at Ceres – Dawn will go into orbit around Ceres and will study the body for approximately five months.
July 2015, End of primary mission – The end of the study of Ceres will mark the completion of the Dawn primary mission. Depending on the health of the spacecraft, the mission might be extended, with possibly other targets to study, but there are no details available at this time.
Please check out the Dawn Mission’s most excellent and informative website:
http://dawn.jpl.nasa.gov/
This week should see the launch of NASA’s mission to very the dawn of our solar system. It’s name? Appropriately enough, Dawn. The goals of the Dawn mission are to understand what it was like at the beginning of the solar system, and to understand how the solar system formed. The mission will do this by making an up-close study of “protoplanets.” According to the current theory of planetary formation, protoplanets are the early stage in the development of planets, condensing out of gas clouds surrounding a young star.
The Dawn mission will carefully examine two of the largest protoplanets that remain. They are Ceres, which has recently been classified as a dwarf planet, and the asteroid Vesta. Both of these bodies orbit the sun with many other smaller bodies in the large area between Mars and Jupiter that is called the asteroid belt. These protoplanets, or baby planets, were interrupted in their process of becoming something larger, by the formation of Jupiter, with its tremendous gravity. Ceres, Vesta, and the rest of the bodies in the asteroid belt have followed different evolutionary paths because of the many different processes that operated during the first few million years of the solar system.
The biggest question that the Dawn mission addresses is the role of size and water in determining the evolution of the planets. Ceres and Vesta are the right two bodies with which to address this question, as they are the most massive of the protoplanets, baby planets whose growth was interrupted by the formation of Jupiter. Ceres is very primitive and wet while Vesta is evolved and dry. The instrumentation to be flown is complete, flight- proven and similar to that used for Mercury, Mars, the Moon, Eros and comets. The science team consists of leading experts in the investigation of the rocky and icy planets using proven measurement and analysis techniques.
Dawn has the potential for making many discoveries that could change the way scientists think. For example, Ceres may have active hydrological (water-based) processes leading to seasonal polar caps of water frost, altering our understanding of the interior of these bodies. Vesta may have rocks more strongly magnetized than on Mars, altering our ideas of how and when dynamos arise with important lessons for Mars, Earth and Mercury. Ceres may have a thin, permanent atmosphere distinguishing it from the other minor planets. These are just examples, but even more unexpected discoveries may be made along the journey.
The Dawn mission has three principal scientific drivers. First, to capture the earliest moments in the origin of the solar system, enabling us to understand the conditions under which these bodies formed. Second, to determine the nature of the building blocks from which the terrestrial planets formed and thereby improve our understanding of this formation. Finally, to contrast the formation and evolution of two small bodies that followed very different evolutionary paths, so that we can understand what controls that evolution.
And continuing the theme of “threes,” the Dawn mission accomplishes three goals for NASA. First, the gathered data will provide some context for interpreting the growing observations of extra solar-planetary systems. Second, the mission will provide information on the role of size and water in planetary evolution and form a bridge between the exploration of the rocky inner solar system and the icy outer solar system. Finally, the mission completes the first order exploration of the inner solar system, addressing NASA's goal of understanding the origin and evolution of the solar system and complements NASA’s ongoing investigations of Mercury, Earth and Mars.
Background on Ceres and Vesta
Ceres is the largest asteroid (designated 1 Ceres), the first to be discovered and was recently designated as a dwarf planet. Ceres is named after the Roman goddess of agriculture. It was discovered by Giuseppe Piazzi of the Palermo Observatory on Jan. 1, 1801. Additional observations by Piazzi were cut short due to illness. Carl Friedrich Gauss, at the age of 24, was able to solve a system of 17 linear equations to determine Ceres' orbit and to allow it to be rediscovered, a remarkable feat for this time. As a result within one year of its initial discovery, both Heinrich Olbers and Franz von Zach were able to relocate Ceres. It revolves around the Sun in 4.6 terrestrial years and has a diameter estimated at about 960 km (600 miles).
Vesta, the brightest asteroid (designated 4 Vesta), is named for the ancient Roman goddess of the hearth and is the only asteroid ever visible with the naked eye. Found on March 29, 1807, by Heinrich Olbers, it was the fourth minor planet to be discovered. It is the second most massive and the third largest asteroid. It revolves around the Sun in 3.6 terrestrial years and has an average diameter of about 520 km (320 miles). Its surface composition is basaltic.
Dawn Mission Timeline
At of this writing, the launch is scheduled for Wednesday, September 26, 2007, with a launch window of 7:25 a.m. - 7:54 a.m. EDT. The eight-year Dawn mission timeline is as follows:
September 2007, Launch – Dawn will launch from … and goes into a solar orbit, moving out to the orbit of the planet Mars.
March 2009, Mars gravity assist – Dawn will make a close approach to Mars and steal a bit of inertia from the planet, making the spacecraft go fast enough to move farther out, toward the main asteroid belt.
September 2011, Arrival at Vesta – Dawn will go into orbit around Vesta and will study the body for approximately seven months.
April 2012, Depart Vesta – Dawn will gradually spiral away from Vesta and begin to journey farther out toward Ceres.
February 2015, Arrival at Ceres – Dawn will go into orbit around Ceres and will study the body for approximately five months.
July 2015, End of primary mission – The end of the study of Ceres will mark the completion of the Dawn primary mission. Depending on the health of the spacecraft, the mission might be extended, with possibly other targets to study, but there are no details available at this time.
Please check out the Dawn Mission’s most excellent and informative website:
http://dawn.jpl.nasa.gov/
Tuesday, September 18, 2007
Deep Impact and Stardust Missions Redesignated
On July 3, NASA announced that Deep Impact and Stardust, two successful comet-study spacecraft, would have their useful lives extended. In a coordinated effort, they will make new observations of comets and also characterize extrasolar planets.
Deep Impact Spacecraft Redesignated for “DIXI” and “EPOCh”
The Deep Impact spacecraft will be committed to two science investigations. The first is called the Deep Impact Extended Investigation (DIXI). The second is called Extrasolar Planet Observation and Characterization (EPOCh).
DIXI will involve the flyby of periodic comet 85P/Boethin, which has not been visited previously. This investigation will allow the recovery of some of the science which was lost with the August 2002 failure of the COmet Nucleus TOUR (CONTOUR) mission that was designed to make comparative studies of multiple comets. The Deep Impact spacecraft will be directed to fly by Boethin on December 5, 2008. Boethin was discovered by an amateur astronomer, the Reverend Leo Boethin, on January 4, 1975. Reverend Boethin discovered the comet, and made the first series of observations, from the town of Abra in the Philippines. The comet has a period of 11.225 years and the next perihelion is predicted to occur June 29, 2008. The rest of the orbital elements are as follows: Aphelion distance, 20,7560 AU; Perihelion distance, 1.1143 AU; Semi-major axis, 11.67560 AU; Eccentricity, 0.7777; Inclination, 5.756 degrees.
While en route to Boethin, the spacecraft will be used for the EPOCh investigation to observe several nearby bright stars, watching as known extrasolar giant planets pass in front of their stars and then behind them. The collected data will be used to characterize the giant planets and to determine whether they possess rings, moons, or Earth-sized planetary companions. EPOCh's sensitivity will exceed both current ground and space-based observatory capabilities. EPOCh also will measure the mid-infrared spectrum of the Earth, providing comparative data for future efforts to study the atmospheres of extrasolar planets.
Stardust Spacecraft Redesignated for “NExT”
While DIXI (Deep Impact) heads elsewhere, the Stardust spacecraft is off to visit Deep Impact’s old friend, periodic Comet 9P/Tempel (or Tempel 1). The mission is called New Exploration of Tempel 1 (NExT). This investigation will provide the first look at the changes to a comet nucleus produced after its close approach to the sun. It will also mark the first time a comet has been revisited. NExT will also extend the mapping of Tempel 1, making it the most mapped comet nucleus to date. The mapping will address the major questions of comet nucleus “geology” raised by images of areas where it appears material might have flowed like a liquid or powder. The images were returned by the Deep Impact spacecraft from its encounter with the comet on July 4, 2005. NExT is scheduled to fly by 9P/Tempel 1 on February 14, 2011. Comet 9P/Tempel was discovered April 3, 1867 by German astronomer Ernst Wilhelm Leberecht Tempel, who was working in Marseille. The comet has a period of 5.515 years and the next perihelion is predicted to occur in 2011. The rest of the orbital elements are as follows: Aphelion distance, 4.737 AU; Perihelion distance, 1.506 AU; Semi-major axis, 3.122 AU; Eccentricity, 0.5175; Inclination, 10.5301 degrees.
Background Information
Stardust was launched February 7, 1999. It traveled over 2 billion miles to fly within 150 miles of the comet Wild 2 in January 2004 to bring back samples that may provide new insights into the composition of comets and how they vary from one another. The container with the comet samples returned to Earth in January 2006 while the rest of the spacecraft remained in space.
Stardust Mission Home Page: http://stardust.jpl.nasa.gov/
Deep Impact was launched January 12, 2005. It traveled 268 million miles to Comet Tempel 1. The two-part spacecraft consisted of a larger “flyby” spacecraft carrying a smaller “impactor” spacecraft. The impactor was released July 2 and impacted Tempel 1 at 10:52 pm PDF on July 3 (July 4 EDT). The flyby spacecraft observed the impact and aftermath from 300 miles away, while other spacecraft and ground instruments made observations.
Deep Impact Mission Home Page: http://deepimpact.jpl.nasa.gov/
On July 3, NASA announced that Deep Impact and Stardust, two successful comet-study spacecraft, would have their useful lives extended. In a coordinated effort, they will make new observations of comets and also characterize extrasolar planets.
Deep Impact Spacecraft Redesignated for “DIXI” and “EPOCh”
The Deep Impact spacecraft will be committed to two science investigations. The first is called the Deep Impact Extended Investigation (DIXI). The second is called Extrasolar Planet Observation and Characterization (EPOCh).
DIXI will involve the flyby of periodic comet 85P/Boethin, which has not been visited previously. This investigation will allow the recovery of some of the science which was lost with the August 2002 failure of the COmet Nucleus TOUR (CONTOUR) mission that was designed to make comparative studies of multiple comets. The Deep Impact spacecraft will be directed to fly by Boethin on December 5, 2008. Boethin was discovered by an amateur astronomer, the Reverend Leo Boethin, on January 4, 1975. Reverend Boethin discovered the comet, and made the first series of observations, from the town of Abra in the Philippines. The comet has a period of 11.225 years and the next perihelion is predicted to occur June 29, 2008. The rest of the orbital elements are as follows: Aphelion distance, 20,7560 AU; Perihelion distance, 1.1143 AU; Semi-major axis, 11.67560 AU; Eccentricity, 0.7777; Inclination, 5.756 degrees.
While en route to Boethin, the spacecraft will be used for the EPOCh investigation to observe several nearby bright stars, watching as known extrasolar giant planets pass in front of their stars and then behind them. The collected data will be used to characterize the giant planets and to determine whether they possess rings, moons, or Earth-sized planetary companions. EPOCh's sensitivity will exceed both current ground and space-based observatory capabilities. EPOCh also will measure the mid-infrared spectrum of the Earth, providing comparative data for future efforts to study the atmospheres of extrasolar planets.
Stardust Spacecraft Redesignated for “NExT”
While DIXI (Deep Impact) heads elsewhere, the Stardust spacecraft is off to visit Deep Impact’s old friend, periodic Comet 9P/Tempel (or Tempel 1). The mission is called New Exploration of Tempel 1 (NExT). This investigation will provide the first look at the changes to a comet nucleus produced after its close approach to the sun. It will also mark the first time a comet has been revisited. NExT will also extend the mapping of Tempel 1, making it the most mapped comet nucleus to date. The mapping will address the major questions of comet nucleus “geology” raised by images of areas where it appears material might have flowed like a liquid or powder. The images were returned by the Deep Impact spacecraft from its encounter with the comet on July 4, 2005. NExT is scheduled to fly by 9P/Tempel 1 on February 14, 2011. Comet 9P/Tempel was discovered April 3, 1867 by German astronomer Ernst Wilhelm Leberecht Tempel, who was working in Marseille. The comet has a period of 5.515 years and the next perihelion is predicted to occur in 2011. The rest of the orbital elements are as follows: Aphelion distance, 4.737 AU; Perihelion distance, 1.506 AU; Semi-major axis, 3.122 AU; Eccentricity, 0.5175; Inclination, 10.5301 degrees.
Background Information
Stardust was launched February 7, 1999. It traveled over 2 billion miles to fly within 150 miles of the comet Wild 2 in January 2004 to bring back samples that may provide new insights into the composition of comets and how they vary from one another. The container with the comet samples returned to Earth in January 2006 while the rest of the spacecraft remained in space.
Stardust Mission Home Page: http://stardust.jpl.nasa.gov/
Deep Impact was launched January 12, 2005. It traveled 268 million miles to Comet Tempel 1. The two-part spacecraft consisted of a larger “flyby” spacecraft carrying a smaller “impactor” spacecraft. The impactor was released July 2 and impacted Tempel 1 at 10:52 pm PDF on July 3 (July 4 EDT). The flyby spacecraft observed the impact and aftermath from 300 miles away, while other spacecraft and ground instruments made observations.
Deep Impact Mission Home Page: http://deepimpact.jpl.nasa.gov/
Saturday, April 21, 2007
Lyrid Meteor Shower
Also called the April Lyrids, meteors from this shower may be visible from April 19 through 25 with the peak (or maximum) normally on April 21/22. The meteors have an irregular rate, but average 12 to 15 per hour. They appear to originate (or radiate) from a point in the constellation of Lyra (Right Ascension 18 hours 16 minutes, Declination +34°) near the bright star Vega. Appearances of this shower have been traced back over 2,500 years. The parent of this shower is Comet Thatcher, 1861 I. The earliest record of the Lyrid shower is from 687 BC.
This year the Lyrid meteor shower is predicted to peak around 6 pm eastern time on April 22. This will be good for Asia, but North America will be in daylight at that time. Still, the shower’s hourly rate around the time of maximum should be at least half as strong as the peak, so observers in North America should catch the rate as it rises in the early-morning hours of April 22 (at least 10 per hour) and as it falls in the early-morning hours of April 22 (again, at least 10 per hour).
Lyrid Meteor Shower History
March 27, 15 BC - A spectacular Lyrid meteor storm was observed. One observer recorded that the "stars fell like rain."
April 20, 1803 - A brilliant Lyrid meteor shower was seen, though an hourly rate of the meteors was not recorded.
April 21, 1922 - A fair display of the Lyrid meteor shower was seen, though an actual hourly rate of meteors is not known.
Observing Meteors
Usually more meteors are seen near midnight and in early mornings, because during that time our part of Earth is facing in the direction of our orbital path, and we are heading into the meteor swarms. Best observing conditions occur with the absence of moonlight, usually when the Moon's phase is between waning crescent and waxing first quarter.
Observers preparing for an evening of observing should bring along a few things: a sleeping bag or blankets for warmth, a recliner or lawn chair, and a hot beverage to help cut the chill. Binoculars are not necessary but they help. Wide-field ones are the best.
In group observing for meteors, each person has his or her own section of the sky to patrol. Wide-field binoculars can help an observer confine his or her attention to their own piece of sky.
Meteor trails make interesting photographs. Also, amateurs with a short-wave radio receiver can "listen" to meteors. This is done by tuning the receiver to a very weak distant station, preferably above 15 megacycles. The volume is kept very low. When a meteor in the upper atmosphere ionizes a patch of air, creating momentary "reflector" for signals, the volume of the station's signal rises sharply. Doppler changes in pitch may occur. On a good morning, several hundred meteors may be heard.
Meteor Activities You Can Do
Also called the April Lyrids, meteors from this shower may be visible from April 19 through 25 with the peak (or maximum) normally on April 21/22. The meteors have an irregular rate, but average 12 to 15 per hour. They appear to originate (or radiate) from a point in the constellation of Lyra (Right Ascension 18 hours 16 minutes, Declination +34°) near the bright star Vega. Appearances of this shower have been traced back over 2,500 years. The parent of this shower is Comet Thatcher, 1861 I. The earliest record of the Lyrid shower is from 687 BC.
This year the Lyrid meteor shower is predicted to peak around 6 pm eastern time on April 22. This will be good for Asia, but North America will be in daylight at that time. Still, the shower’s hourly rate around the time of maximum should be at least half as strong as the peak, so observers in North America should catch the rate as it rises in the early-morning hours of April 22 (at least 10 per hour) and as it falls in the early-morning hours of April 22 (again, at least 10 per hour).
Lyrid Meteor Shower History
March 27, 15 BC - A spectacular Lyrid meteor storm was observed. One observer recorded that the "stars fell like rain."
April 20, 1803 - A brilliant Lyrid meteor shower was seen, though an hourly rate of the meteors was not recorded.
April 21, 1922 - A fair display of the Lyrid meteor shower was seen, though an actual hourly rate of meteors is not known.
Observing Meteors
Usually more meteors are seen near midnight and in early mornings, because during that time our part of Earth is facing in the direction of our orbital path, and we are heading into the meteor swarms. Best observing conditions occur with the absence of moonlight, usually when the Moon's phase is between waning crescent and waxing first quarter.
Observers preparing for an evening of observing should bring along a few things: a sleeping bag or blankets for warmth, a recliner or lawn chair, and a hot beverage to help cut the chill. Binoculars are not necessary but they help. Wide-field ones are the best.
In group observing for meteors, each person has his or her own section of the sky to patrol. Wide-field binoculars can help an observer confine his or her attention to their own piece of sky.
Meteor trails make interesting photographs. Also, amateurs with a short-wave radio receiver can "listen" to meteors. This is done by tuning the receiver to a very weak distant station, preferably above 15 megacycles. The volume is kept very low. When a meteor in the upper atmosphere ionizes a patch of air, creating momentary "reflector" for signals, the volume of the station's signal rises sharply. Doppler changes in pitch may occur. On a good morning, several hundred meteors may be heard.
Meteor Activities You Can Do
- Observe showers, alone or with groups.
- Count the number of meteors seen in an hour. If observing a shower, count the number per minute.
- On a star chart, plot the beginning and ending points of meteor trails.
- If a meteor falls in your vicinity, try to find it. Watch your local newspaper for a report. Find persons who saw the meteor fall and attempt to trace it. Cooperate with a nearby observatory or museum, if any.
The above material is taken from the document, Meteoroids, Meteors, Meteorites and Tektites by James M. Thomas, last revised September 2, 2004.
Friday, August 25, 2006
Constellations, their Lore and Meaning
I hope you are making plans to be with us Friday evening, September 1, for the next in our series of astronomy presentations co-sponsored by Museum Astronomical Resource Society and the Science Library at MOSI.
Our presentation will be "Constellations, their Lore and Meaning." Though harder to see above our modern cities, the stars and their groupings still grace our nighttime skies, ever ready to tell us a story, tell us the time and give us direction on a clear night. Come learn how the constellations got their names and how they can help us today.
The presentation will be held Friday, September 1, from 7:00 PM to 8:00 PM in the Saunders Planetarium at MOSI in Tampa. As always, the presentation is free and open to the public. This is the fifth of our six presentations scheduled for 2006. We hope to see you there!
Clear Skies,
Jimmy Thomas
I hope you are making plans to be with us Friday evening, September 1, for the next in our series of astronomy presentations co-sponsored by Museum Astronomical Resource Society and the Science Library at MOSI.
Our presentation will be "Constellations, their Lore and Meaning." Though harder to see above our modern cities, the stars and their groupings still grace our nighttime skies, ever ready to tell us a story, tell us the time and give us direction on a clear night. Come learn how the constellations got their names and how they can help us today.
The presentation will be held Friday, September 1, from 7:00 PM to 8:00 PM in the Saunders Planetarium at MOSI in Tampa. As always, the presentation is free and open to the public. This is the fifth of our six presentations scheduled for 2006. We hope to see you there!
Clear Skies,
Jimmy Thomas
Thursday, August 24, 2006
The Votes Are In, Pluto Is Out
Hello, friends.
It is a momentous day, August 24, 2006. Following a week of heated debate at the IAU General Assembly in Prague, the results of the voting during today's closing ceremonies are known.
The designation of Pluto has changed from "planet" to "dwarf planet," as defined in item 2 of Resolution 5A, below. Pluto is joined in this designation by Ceres and 2003 UB313. Charon will not receive this "dwarf planet" designation, remaining simply a satellite of Pluto. The current solar system planetary count is a follows: 8 planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune), and 3 dwarf planets (Ceres, Pluto, and 2003 UB313).
Please note that Pluto did not loose its "planet" designation because of its size, but because it did not fulfill its "planetary housekeeping" obligation of clearing out the neighborhood of its orbit. Since Pluto crosses the orbit of Neptune, it is evident that Pluto was not able to steak a claim for itself by gobbling up all of the adjacent matter and become the regional king of the hill, as the now eight solar system planets were able to do during their planetary formation.
For a look at the final draft of these resolutions, follow this link:
(http://www.iau2006.org/mirror/www.iau.org/iau0602/index.html)
To view the full new release on results of the voting, follow this link:
(http://www.iau2006.org/mirror/www.iau.org/iau0603/index.html)
Below is the text of the related IAU Resolutions 5A and 6A:
I should note that a proposed Resolution 5B recommend that the eight planets be described as “classical” planet, and proposed Resolution 6B recommended that the new class of Pluto-type bodies be called “plutonian objects.” However, neither of these resolutions was accepted during this meeting. The matter regarding Resolution 6B will be considered further by the IAU.
**************
RESOLUTIONS
Resolution 5A is the principal definition for the IAU usage of "planet" and related terms.
Resolution 6A creates for IAU usage a new class of objects, for which Pluto is the prototype. The IAU will set up a process to name these objects.
IAU Resolution: Definition of a Planet in the Solar System
Contemporary observations are changing our understanding of planetary systems, and it is important that our nomenclature for objects reflect our current understanding. This applies, in particular, to the designation 'planets'. The word 'planet' originally described 'wanderers' that were known only as moving lights in the sky. Recent discoveries lead us to create a new definition, which we can make using currently available scientific information.
RESOLUTION 5A
The IAU therefore resolves that "planets" and other bodies in our Solar System be defined into three distinct categories in the following way:
(1) A "planet"(see footnote 1) is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit.
(2) A "dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape(see footnote 2) , (c) has not cleared the neighborhood around its orbit, and (d) is not a satellite.
(3) All other objects(see footnote 3) except satellites orbiting the Sun shall be referred to collectively as "Small Solar-System Bodies".
----------
Footnote 1: The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
Footnote 2: An IAU process will be established to assign borderline objects into either dwarf planet and other categories.
Footnote 3: These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.
----------
IAU Resolution: Pluto
RESOLUTION 6A
The IAU further resolves:
Pluto is a "dwarf planet" by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects.
**************
Clear Skies,
Jimmy Thomas
Hello, friends.
It is a momentous day, August 24, 2006. Following a week of heated debate at the IAU General Assembly in Prague, the results of the voting during today's closing ceremonies are known.
The designation of Pluto has changed from "planet" to "dwarf planet," as defined in item 2 of Resolution 5A, below. Pluto is joined in this designation by Ceres and 2003 UB313. Charon will not receive this "dwarf planet" designation, remaining simply a satellite of Pluto. The current solar system planetary count is a follows: 8 planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune), and 3 dwarf planets (Ceres, Pluto, and 2003 UB313).
Please note that Pluto did not loose its "planet" designation because of its size, but because it did not fulfill its "planetary housekeeping" obligation of clearing out the neighborhood of its orbit. Since Pluto crosses the orbit of Neptune, it is evident that Pluto was not able to steak a claim for itself by gobbling up all of the adjacent matter and become the regional king of the hill, as the now eight solar system planets were able to do during their planetary formation.
For a look at the final draft of these resolutions, follow this link:
(http://www.iau2006.org/mirror/www.iau.org/iau0602/index.html)
To view the full new release on results of the voting, follow this link:
(http://www.iau2006.org/mirror/www.iau.org/iau0603/index.html)
Below is the text of the related IAU Resolutions 5A and 6A:
I should note that a proposed Resolution 5B recommend that the eight planets be described as “classical” planet, and proposed Resolution 6B recommended that the new class of Pluto-type bodies be called “plutonian objects.” However, neither of these resolutions was accepted during this meeting. The matter regarding Resolution 6B will be considered further by the IAU.
**************
RESOLUTIONS
Resolution 5A is the principal definition for the IAU usage of "planet" and related terms.
Resolution 6A creates for IAU usage a new class of objects, for which Pluto is the prototype. The IAU will set up a process to name these objects.
IAU Resolution: Definition of a Planet in the Solar System
Contemporary observations are changing our understanding of planetary systems, and it is important that our nomenclature for objects reflect our current understanding. This applies, in particular, to the designation 'planets'. The word 'planet' originally described 'wanderers' that were known only as moving lights in the sky. Recent discoveries lead us to create a new definition, which we can make using currently available scientific information.
RESOLUTION 5A
The IAU therefore resolves that "planets" and other bodies in our Solar System be defined into three distinct categories in the following way:
(1) A "planet"(see footnote 1) is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit.
(2) A "dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape(see footnote 2) , (c) has not cleared the neighborhood around its orbit, and (d) is not a satellite.
(3) All other objects(see footnote 3) except satellites orbiting the Sun shall be referred to collectively as "Small Solar-System Bodies".
----------
Footnote 1: The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
Footnote 2: An IAU process will be established to assign borderline objects into either dwarf planet and other categories.
Footnote 3: These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.
----------
IAU Resolution: Pluto
RESOLUTION 6A
The IAU further resolves:
Pluto is a "dwarf planet" by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects.
**************
Clear Skies,
Jimmy Thomas
Wednesday, August 16, 2006
Proposed New Definition for a Planet
Hello, friends.
For years, astronomers have been debating the definition of a planet. Today, August 16, the International Astronomical Union's Planet Definition Committee announced their proposal for a new, official definition of "planet." If the proposal is approved by a vote of IAU astronomers on August 24th, the number of planets in the Solar System would swell from nine to twelve.
The International Astronomical Union (IAU) is an organization that brings together distinguished astronomers from all nations of the world. IAU's mission is to promote and safeguard the science of astronomy in all its aspects through international cooperation. Founded in 1919, the IAU is the world's largest professional body for astronomers. The IAU General Assembly is held every three years and is one of the largest and most diverse meetings in the astronomical community's calendar. (URL: http://www.iau.org)
All of the IAU material on this announcement, including text, images and animation, is available at the following URL:
http://www.iau2006.org/mirror/www.iau.org/iau0601/iau0601_release.html
Below is the text from today's press release:
**********
The IAU draft definition of "planet" and "plutons"
16. August 2006, Prague
The world's astronomers, under the auspices of the International Astronomical Union (IAU), have concluded two years of work defining the difference between "planets" and the smaller "solar system bodies" such as comets and asteroids. If the definition is approved by the astronomers gathered 14-25 August 2006 at the IAU General Assembly in Prague, our Solar System will include 12 planets, with more to come: eight classical planets that dominate the system, three planets in a new and growing category of "plutons" - Pluto-like objects - and Ceres. Pluto remains a planet and is the prototype for the new category of "plutons."
With the advent of powerful new telescopes on the ground and in space, planetary astronomy has gone though an exciting development over the past decade. For thousands of years very little was known about the planets other than they were objects that moved in the sky with respect to the background of fixed stars. In fact the word "planet" comes from the Greek word for "wanderer". But today hosts of newly discovered large objects in the outer regions of our Solar System present a challenge to our historically based definition of a "planet".
At first glance one should think that it is easy to define what a planet is - a large and round body. On second thought difficulties arise, as one could ask "where is the lower limit?" - how large, and how round should an asteroid be before it becomes a planet - as well as "where is the upper limit?" - how large can a planet be before it becomes a brown dwarf or a star?
IAU President Ron Ekers explains the rational behind a planet definition: "Modern science provides much more knowledge than the simple fact that objects orbiting the Sun appear to move with respect to the background of fixed stars. For example, recent new discoveries have been made of objects in the outer regions of our Solar System that have sizes comparable to and larger than Pluto. These discoveries have rightfully called into question whether or not they should be considered as new 'planets.' "
The International Astronomical Union has been the arbiter of planetary and satellite nomenclature since its inception in 1919. The world's astronomers, under the auspices of the IAU, have had official deliberations on a new definition for the word "planet" for nearly two years. IAU's top, the so-called Executive Committee, led by Ekers, formed a Planet Definition Committee (PDC) comprised by seven persons who were astronomers, writers, and historians with broad international representation. This group of seven convened in Paris in late June and early July 2006. They culminated the two year process by reaching a unanimous consensus for a proposed new definition of the word "planet."
Owen Gingerich, the Chair of the Planet Definition Committee says: "In July we had vigorous discussions of both the scientific and the cultural/historical issues, and on the second morning several members admitted that they had not slept well, worrying that we would not be able to reach a consensus. But by the end of a long day, the miracle had happened: we had reached a unanimous agreement."
The part of "IAU Resolution 5 for GA-XXVI" that describes the planet definition, states "A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet." Member of the Planet Definition Committee, Richard Binzel says: "Our goal was to find a scientific basis for a new definition of planet and we chose gravity as the determining factor. Nature decides whether or not an object is a planet."
According to the new draft definition, two conditions must be satisfied for an object to be called a "planet." First, the object must be in orbit around a star, while not being itself a star. Second, the object must be large enough (or more technically correct, massive enough) for its own gravity to pull it into a nearly spherical shape. The shape of objects with mass above 5 x 1020 kg and diameter greater than 800 km would normally be determined by self-gravity, but all borderline cases would have to be established by observation.
If the proposed Resolution is passed, the 12 planets in our Solar System will be Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Charon and 2003 UB313. The name 2003 UB313 is provisional, as a "real" name has not yet been assigned to this object. A decision and announcement of a new name are likely not to be made during the IAU General Assembly in Prague, but at a later time. The naming procedures depend on the outcome of the Resolution vote. There will most likely be more planets announced by the IAU in the future. Currently a dozen "candidate planets" are listed on IAU's "watchlist" which keeps changing as new objects are found and the physics of the existing candidates becomes better known.
The IAU draft Resolution also defines a new category of planet for official use: "pluton". Plutons are distinguished from classical planets in that they reside in orbits around the Sun that take longer than 200 years to complete (i.e. they orbit beyond Neptune). Plutons typically have orbits that are highly tilted with respect to the classical planets (technically referred to as a large orbital inclination). Plutons also typically have orbits that are far from being perfectly circular (technically referred to as having a large orbital eccentricity). All of these distinguishing characteristics for plutons are scientifically interesting in that they suggest a different origin from the classical planets.
The draft "Planet Definition" Resolution will be discussed and refined during the General Assembly and then it (plus four other Resolutions) will be presented for voting at the 2nd session of the GA 24 August between 14:00 and 17:30 CEST.
**********
Clear Skies,
Jimmy Thomas
Hello, friends.
For years, astronomers have been debating the definition of a planet. Today, August 16, the International Astronomical Union's Planet Definition Committee announced their proposal for a new, official definition of "planet." If the proposal is approved by a vote of IAU astronomers on August 24th, the number of planets in the Solar System would swell from nine to twelve.
The International Astronomical Union (IAU) is an organization that brings together distinguished astronomers from all nations of the world. IAU's mission is to promote and safeguard the science of astronomy in all its aspects through international cooperation. Founded in 1919, the IAU is the world's largest professional body for astronomers. The IAU General Assembly is held every three years and is one of the largest and most diverse meetings in the astronomical community's calendar. (URL: http://www.iau.org)
All of the IAU material on this announcement, including text, images and animation, is available at the following URL:
http://www.iau2006.org/mirror/www.iau.org/iau0601/iau0601_release.html
Below is the text from today's press release:
**********
The IAU draft definition of "planet" and "plutons"
16. August 2006, Prague
The world's astronomers, under the auspices of the International Astronomical Union (IAU), have concluded two years of work defining the difference between "planets" and the smaller "solar system bodies" such as comets and asteroids. If the definition is approved by the astronomers gathered 14-25 August 2006 at the IAU General Assembly in Prague, our Solar System will include 12 planets, with more to come: eight classical planets that dominate the system, three planets in a new and growing category of "plutons" - Pluto-like objects - and Ceres. Pluto remains a planet and is the prototype for the new category of "plutons."
With the advent of powerful new telescopes on the ground and in space, planetary astronomy has gone though an exciting development over the past decade. For thousands of years very little was known about the planets other than they were objects that moved in the sky with respect to the background of fixed stars. In fact the word "planet" comes from the Greek word for "wanderer". But today hosts of newly discovered large objects in the outer regions of our Solar System present a challenge to our historically based definition of a "planet".
At first glance one should think that it is easy to define what a planet is - a large and round body. On second thought difficulties arise, as one could ask "where is the lower limit?" - how large, and how round should an asteroid be before it becomes a planet - as well as "where is the upper limit?" - how large can a planet be before it becomes a brown dwarf or a star?
IAU President Ron Ekers explains the rational behind a planet definition: "Modern science provides much more knowledge than the simple fact that objects orbiting the Sun appear to move with respect to the background of fixed stars. For example, recent new discoveries have been made of objects in the outer regions of our Solar System that have sizes comparable to and larger than Pluto. These discoveries have rightfully called into question whether or not they should be considered as new 'planets.' "
The International Astronomical Union has been the arbiter of planetary and satellite nomenclature since its inception in 1919. The world's astronomers, under the auspices of the IAU, have had official deliberations on a new definition for the word "planet" for nearly two years. IAU's top, the so-called Executive Committee, led by Ekers, formed a Planet Definition Committee (PDC) comprised by seven persons who were astronomers, writers, and historians with broad international representation. This group of seven convened in Paris in late June and early July 2006. They culminated the two year process by reaching a unanimous consensus for a proposed new definition of the word "planet."
Owen Gingerich, the Chair of the Planet Definition Committee says: "In July we had vigorous discussions of both the scientific and the cultural/historical issues, and on the second morning several members admitted that they had not slept well, worrying that we would not be able to reach a consensus. But by the end of a long day, the miracle had happened: we had reached a unanimous agreement."
The part of "IAU Resolution 5 for GA-XXVI" that describes the planet definition, states "A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet." Member of the Planet Definition Committee, Richard Binzel says: "Our goal was to find a scientific basis for a new definition of planet and we chose gravity as the determining factor. Nature decides whether or not an object is a planet."
According to the new draft definition, two conditions must be satisfied for an object to be called a "planet." First, the object must be in orbit around a star, while not being itself a star. Second, the object must be large enough (or more technically correct, massive enough) for its own gravity to pull it into a nearly spherical shape. The shape of objects with mass above 5 x 1020 kg and diameter greater than 800 km would normally be determined by self-gravity, but all borderline cases would have to be established by observation.
If the proposed Resolution is passed, the 12 planets in our Solar System will be Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Charon and 2003 UB313. The name 2003 UB313 is provisional, as a "real" name has not yet been assigned to this object. A decision and announcement of a new name are likely not to be made during the IAU General Assembly in Prague, but at a later time. The naming procedures depend on the outcome of the Resolution vote. There will most likely be more planets announced by the IAU in the future. Currently a dozen "candidate planets" are listed on IAU's "watchlist" which keeps changing as new objects are found and the physics of the existing candidates becomes better known.
The IAU draft Resolution also defines a new category of planet for official use: "pluton". Plutons are distinguished from classical planets in that they reside in orbits around the Sun that take longer than 200 years to complete (i.e. they orbit beyond Neptune). Plutons typically have orbits that are highly tilted with respect to the classical planets (technically referred to as a large orbital inclination). Plutons also typically have orbits that are far from being perfectly circular (technically referred to as having a large orbital eccentricity). All of these distinguishing characteristics for plutons are scientifically interesting in that they suggest a different origin from the classical planets.
The draft "Planet Definition" Resolution will be discussed and refined during the General Assembly and then it (plus four other Resolutions) will be presented for voting at the 2nd session of the GA 24 August between 14:00 and 17:30 CEST.
**********
Clear Skies,
Jimmy Thomas
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