Tuesday, September 28, 2010

Ismaël Bullialdus
I thought I would take this opportunity to wish a very happy birthday to Ismaël Bullialdus. Who is that, you say? I must confess that until very recently I, too, was ignorant of this gentleman. Please allow me to enlighten...
Ismaël Bullialdus
Born September 28, 1605 in Loudun, Vienne, France; Died November 25, 1694 (aged 89) in Abbey St Victor, Paris, France
Over the course of his life, Bullialdus was a Catholic priest, a librarian, an author, a notary, and an amateur astronomer. He was born Ismaël Boulliau, the first surviving son of Calvinist parents, Susanna Motet and Ismaël Boulliau. At age twenty-one their son Ismaël converted to Catholicism, and by twenty-six was ordained as a priest. In 1632 Ismaël moved to Paris, where he worked as a librarian for the Bibliothèque du Roi--the first royal library of France--along with his brothers Pierre and Jacques Dupuy. The three traveled widely within Italy, Holland, and Germany, purchasing books for the library. In 1657 Ismaël took the position of secretary to the French ambassador to Holland. But he soon returned to the role of librarian and, in 1666, moved to the Collège de Laon--now the University of Paris. During the last five years of his life, Ismaël returned to the priesthood at the Abbey St Victor in Paris, where he died in 1694.
Seventeenth century rendering of Ismaël Boulliau (Ismaël Bullialdus), 1605-1694.
Because of his various interests, Ismaël was a friend to many notable persons in the overlapping worlds of philosophy, religion, science, astronomy, and mathematics. The list of associations included Pierre Gassendi (1592-1655), Christiaan Huygens (1629-1695), Marin Mersenne (1588-1648), and Blaise Pascal (1623-1662). In addition, Ismaël was an active supporter of the works and writings of Galileo Galilei (1554-1642) and Nicolaus Copernicus (1473-1543).
Ismaël is best remembered for his astronomical and mathematical works. And because Latin was the predominant crossover language for Western European countries, the text of most publications was also in Latin, as well as a Latin-ized version of the author’s name. This is how Ismaël Boulliau also became known as Ismaël Bullialdus.
Chief among Ismaël’s works is his Atronsomia philolaica (1645). In this work he strongly supported the hypothesis of Johannes Kepler (1571-1630) which stated that the planets travel in elliptical orbits around the Sun, but Ismaël argued against the physical theory that Kepler had proposed to explain them. In particular, Ismaël objected to Kepler's proposal that the strength of the force exerted on the planets by the Sun (which we would call gravitational force) decreases in inverse proportion to their distance from it. Ismaël argued that if such a force existed it would instead have to follow an inverse-square law--the first astronomer to suggest this, now accepted law. Even so, Bullialdus did not believe that any such force did in fact exist. In his Principia Mathematica of 1687, Isaac Newton (1643-1727) acknowledged that Bullialdus's determination of the sizes of the planets' orbits ranked with Kepler's as the most accurate then available.
Bullialdus was one of the earliest members of the Royal Society, London, having been elected on April 4, 1667, seven years after its founding. The Moon's Bullialdus crater is named in his honor.
Bullialdus on the Moon
An interesting tie-in to this birthday celebration is a view at lunar crater named for our birthday boy.
The central peak of Bullialdus crater, taken by NASA's Lunar Reconnaissance Orbiter (LRO). Image Credit: NASA/GSFC/Arizona State University
The above image shows the summit of the central peak of Bullialdus crater, located in the western part of Mare Nubium (coordinates 20.7°S 22.2°W). The central peak of Bullialdus is about a kilometer high.
The above image show the full 60 km-diameter Bullialdus crater. The arrow indicates the location of the central peak. Image Credit: NASA/GSFC/Arizona State University
Bullialdus crater has been studied by terrestrial observatories, BMDO/NASA's Clementine spacecraft, and NASA's Lunar Reconnaissance Orbiter (LRO). For more on Bullialdus crater, the Lunar Reconnaissance Orbiter mission and the Clementine mission, check out these links:
More from the LRO mission site on Bullialdus crater
NASA's Lunar Reconnaissance Orbiter (LRO)
NSSDC - Clementine Project Information

Sunday, September 26, 2010

Sunday marks the fifth anniversary of the flyby of Saturn’s moon Hyperion by NASA’s Cassini spacecraft. The moon Hyperion (pronounced “hi-PEER-e-on”) is one of the known moons of Saturn--53 as of this writing. Hyperion has been imaged several times from moderate distances by NASA’s Cassini spacecraft, but has been studied closely only once, at a fly-by distance of 500 kilometers, on September 26, 2005. Hyperion is best distinguished by its irregular shape, chaotic rotation and sponge-like appearance. No future missions to this small body are currently planned.
The image is an approximately true color mosaic of Hyperion. Composed of several narrow-angle frames and processed to match Hyperion’s natural color, the images were taken during Cassini’s flyby of the moon on September 26, 2005. Image Credit: NASA
In Greek mythology Hyperion (Greek, meaning “The High-One”) was one of the twelve Titans--the generation that preceded the more well-known Greek gods. Hyperion was the brother of Cronus (in Roman mythology, Saturn), and Hyperion was also the lord of light. He was the son of Gaia (the physical incarnation or Earth) and Uranus (Greek, meaning "the Sky").
The moon was discovered in 1848 by astronomers William Cranch Bond, George Phillips Bond and William Lassell. The discovery came shortly after astronomer John Herschel had published possible names for the seven previously-known satellites of Saturn in 1847. Lassell saw the new moon two days before the Bonds and was already in favor of Herschel’s naming scheme, and so suggested the name Hyperion in accordance with that scheme and managed to publish ahead of the Bonds.
Spacecraft Visits
Cassini was the second spacecraft to study Hyperion at a moderate distance. NASA’s Voyager 2 passed through the Saturn system in 1979 and discerned individual craters on Hyperion as well as an enormous ridge. Cassini’s early images suggested that it had an unusual appearance, but it was not until Cassini’s close flyby that the oddness of this moon was fully revealed. The surface is covered with deep, sharp-edged craters that give Hyperion the appearance of a giant sponge. The rough dimensions are 328 km by 260 km by 214 km. There is dark, reddish material in the bottom of each crater. Spectroscopic analysis finds that this material contains carbon and hydrogen and it appears very similar to material found on other Saturn moons. The accumulated data indicate that about 40 percent of Hyperion is empty space. Also, the material that is there is mostly water ice with a very little amount of rock.
Density and Coloration
The low density of Hyperion indicates that the moon is composed largely of water ice with only a small amount of rock. Astronomers think that the composition of Hyperion may be similar to a loosely accreted pile of rubble. However, unlike most of Saturn’s moons, Hyperion has a low albedo--the ratio of reflected to incident light. Hyperion’s albedo is 0.2-0.3, indicating that it is covered by at least a thin layer of dark material. Two candidate have been suggested for the source of the dark material. One is darker, nearby moon Phoebe. The other is the closer moon Iapetus. Since the dark material has a reddish tint, and since Iapetus is reddish, this would suggest that Iapetus is the more likely source of the two, if at all.
Let’s color-compare. The above image is a combination of three moons. Phoebe is on the left, two-toned Iapetus is in the middle and Hyperion is on the right. The moons are not shown in relative scale with each other. All Images Credit: NASA

To learn more about Hyperion, the Saturn system, and the spacecraft visitors to Hyperion, check out these sites:
NASA Solar System Exploration - Saturn System

NASA World Book - Saturn

NASA Cassini Mission

NASA Voyager - the Interstellar Mission

Wednesday, September 22, 2010

Jupiter Opposition 2010

Better late than never. Check out Jupiter, now at opposition! 

I realize that I told you about the opposition of Uranus without evening mentioning the simultaneous opposition of one of the most prominent objects in our nighttime sky--the planet Jupiter. Jupiter’s opposition for this year occurs over September 20-21, but if you cannot see it tonight, check it out over the next evening or two. It will still be just as beautiful. Jupiter will be rising in the east as the sun sets in the west. Only Earth’s moon will be brighter than Jupiter.

A composite of 4 images of Jupiter, taken December 7, 2000 by the NASA Cassini spacecraft. The moon Europa is casting a shadow on the planet at the lower-left. Image Credit: NASA/JPL/University of Arizona

Earth’s encounters with Jupiter happen every 13 months when Earth--the inner planet--laps Jupiter in their race around the sun. Earth and Jupiter do not orbit the sun in perfect circles, so they are not aways the same distance apart when Earth passes. On September 20-21, Jupiter will be as much as 75 million km closer than in previous encounters and will not be this close again until 2022.

When viewed through a telescope, the disk of Jupiter can be seen in rare detail. For instance, the Great Red Spot, a cyclone about twice as wide as Earth, is bumping against a smaller storm which has been nicknamed “Red Spot Jr.” 

In addition, Jupiter’s distinctive South Equatorial Belt recently vanished, possibly submerged beneath high clouds. Astronomers suggest that it could reappear at any time, accompanied by many new spots and swirls, all visible in backyard telescopes.

And amateur astronomers have recently reported a significant number of fireballs in Jupiter’s atmosphere. This is the apparent result of many small asteroids or comet fragments that are hitting Jupiter and exploding among the clouds. Researchers of these events have suggested that observers could see visible flashes as often as a few times a month.

Of course, we must not forget the four largest moons of Jupiter, which are visible even with a modest pair of binoculars. Since Galileo Galilei’s discovery of these planet-sized worlds 400 years ago, we have learned that one has active volcanoes (Io), one possibly has underground oceans (Europa), one has vast fields of craters (Callisto), and one has mysterious global grooves (Ganymede). In modern amateur telescopes, these appear as planetary disks with colorful markings.

A “family portrait” of Jupiter and its four largest moons. From top to bottom, the moons shown are Io, Europa, Ganymede and Callisto. The image is a composite, with the size of the moons and the planet in scale. The images of all but Callisto were taken by the NASA Galileo spacecraft. The orbital path of Galileo and the nature of the study of Callisto prevented a good image of the moon as a whole. The image of Callisto seen here was taken in 1979 by the NASA Voyager spacecraft. Image Credit NASA

More on Jupiter

Jupiter is the fifth planet from our sun and the largest planet in our solar system. Jupiter is a gas giant, having a mass a little less than 1/1000 that of the sun while 2-1/2 times the mass of all the remaining gas giants--Saturn, Uranus, Neptune. These four are are sometimes described as the Jovian planets--the planets that share many of the characteristics of Jupiter (Jove).

Quick trivia, by Jove! The king of the Roman gods was first called Jove. Later he was described as Father Jove--in Old Latin, “Jovis Pater.” Over the generations this phrase was gradually slurred and abbreviated, becoming Jupiter.

As seen from Earth, Jupiter reaches an apparent magnitude of -2.94--on average, the third-brightest object in our sky after Earth’s moon and Venus. 

One quarter of Jupiter’s mass is helium, with rest being mostly hydrogen. Astronomers think there may be a rocky core of heavier elements. Jupiter has a very rapid rotation, causing the planet to bulge at the equator, a shape known as an oblate spheroid. Jupiter’s outer atmosphere is divided into several bands at different latitudes, with storms along the boundaries of each of the bands. One result is the prominent feature known as the Great Red Spot, a giant storm that has existed at least since the seventeenth century, when it was first observed by telescope. Jupiter is surrounded by a faint ring system and a powerful magnetosphere. And as of this writing, Jupiter has at least 63 moons, including the four large Galilean moons--those moons first observed in 1610 by Galileo Galilei. They are Ganymede, Callisto, Europa, and Io. The largest of these is Ganymede, having a diameter greater than the planet Mercury.

This time-lapse video records the Voyager 1 spacecraft’s approach to Jupiter during a period of over 60 days, prior to its closest approach on March 5, 1979. Image Credit: NASA/JPL

The planet Jupiter has been explored by several NASA robotic spacecraft. In chronological order, they are Pioneer 10 (flyby 1973), Pioneer 11 (flyby 1974), Voyager 1 (flyby 1979), Voyager 2 (flyby 1979), Galileo (orbiter 1995-2003), Cassini (flyby 2001), and New Horizons (flyby 2007). 

Future Mission, Juno

Currently in development is the NASA Juno mission to study how Jupiter formed and became the dynamic world we see today. The solar-powered Juno spacecraft will map the gravity field, magnetic field and atmospheric structure of Jupiter from a unique polar orbit. Juno's observations will lead to a better understanding of the formation of our solar system and planetary systems discovered around other stars.

Artist concept of the Juno spacecraft at Jupiter. Image Credit: NASA/JPL

The Juno mission launch window opens August 5, 2011. The spacecraft will then undergo a five-year cruise, arriving at Jupiter in July of 2016. Once at Jupiter, the spacecraft will spend the next year orbiting the planet 32 times. Specifically, Juno will...

1. Determine how much water is in Jupiter’s atmosphere, which helps determine which planet formation theory is correct, or whether a new theory is needed

2. Look deep into Jupiter’s atmosphere to measure composition, temperature, cloud motions and other properties

3. Map Jupiter’s magnetic and gravity fields, revealing the planet’s deep structure

4. Explore and study Jupiter’s magnetosphere near the planet’s poles, especially the auroras--Jupiter’s northern and southern lights--providing new insights about how the planet’s enormous magnetic force field affects its atmosphere.

To learn more about the planet Jupiter, past missions and future missions, check out these links.

NASA Solar System Exploration - Jupiter

NASA Solar System Exploration - Galileo Legacy Site

NASA Juno Mission


Tuesday, September 21, 2010

Uranus at Opposition 2010

Tuesday, September 21, marks the opposition of Uranus—the point in Uranus’ orbit where it appears in  Earth’s sky opposite from the sun. The planet can be found wandering between the constellations Pisces and Cetus. Uranus can be easy to see, but not so easy to recognize as a planet. If you have charts, then you can find dim Uranus in a clear, very dark sky using binoculars or even naked-eye. When using a telescope of aperture 10 inches or larger, the planet may appear blue-green in color. The publishers of Sky and Telescope have a basic chart here:        

More on Uranus

The planet Uranus is the seventh planet from the sun, the third-largest planet in our solar system, and the fourth most massive planet our solar system. Uranus is named after the ancient Greek god of the sky, who was also the father of Cronus (Roman, Saturn) and the grandfather of Zeus (Roman, Jupiter). Like the five classical planets (Mercury, Venus, Mars, Jupiter, and Saturn), Uranus is visible to the naked eye, but it was not recognized as a planet by ancient astronomers because of its dimness and slow orbit. Its discovery, the first made using a telescope, was announced on March 13, 1781 by German-British astronomer Sir William Herschel.

NASA's Voyager 2 spacecraft at Uranus. Image Credit NASA

Like the planet Neptune, Uranus shares similarities to Jupiter and Saturn in that they consist primarily of hydrogen and helium. But unlike Jupiter and Saturn, the pair also has lots of water, ammonia, methane, and traces of hydrocarbons. Uranus has the coldest planetary atmosphere in the solar system, with a minimum temperature of 49 Kelvins (-224 degrees Celsius). The cloud structure is complex and layered, with water thought to make up the lowest-level clouds, and methane thought to make up the highest-level clouds. The interior of Uranus is composed mainly of ices and rock.

Like all gas giants (Jupiter, Saturn, Uranus, and Neptune), has a ring system, and magnetosphere, and many moons. But the Uranian system is different from the others in that its axis of rotation is tilted sideways, nearly into the plane of Uranus’ orbit. As seen from Earth, the Uranian rings can sometimes appear as circles around the planet, and sometimes appear edge-on. In 1986, the NASA Voyager 2 spacecraft transmitted to Earth images of Uranus as it flew by. In those images, Uranus appeared as a virtually featureless planet in visible light without the cloud bands or storms that astronomers associate with the other gas giants. But images taken from Earth in recent years have shown signs of seasonal change and increased weather activity, as Uranus approached its equinox. The wind speeds on Uranus can reach 250 meters per second (900 km/h, or 560 mph).

Voyager at Uranus

Launched on August 20, 1977, the Voyager 2 spacecraft passed closest to the planet Uranus on January 24, 1986, coming within 81,500 kilometers (50,600 miles) of the cloudtops. Voyager 2's images of the five largest moons around Uranus revealed complex surfaces indicative of varying geologic pasts. The cameras also detected 10 previously unseen moons. Several instruments studied the ring system, uncovering the fine detail of the previously known rings and two newly detected rings. Voyager data showed that the planet's rate of rotation is 17 hours, 14 minutes. The spacecraft also found a Uranian magnetic field that is both large and unusual. In addition, the temperature of the equatorial region, which receives less sunlight over a Uranian year, is nevertheless about the same as that at the poles.

Voyager 2 image of a crescent-Uranus after passing beyond the planet. Image Credit: NASA

For more on the planet Uranus, the Voyager program and the ongoing Voyager Interstellar Mission, visit these links:

NASA - Solar System Exploration - Uranus

NASA/JPL - Voyager, the Interstellar Mission

NSSDC - Voyager Project Information

Saturday, September 18, 2010

Observe the Moon Tonight!

Tonight, Saturday, September 18, the world will join the NASA Goddard Space Flight Center’s Visitor Center in Greenbelt, Maryland, as well as other NASA Centers to celebrate the first annual International Observe the Moon Night (InOMN).
Earth's Moon. Image Credit NASA.

InOMN provides the opportunity for the general public, NASA partners, and amateur astronomers to learn about lunar science and to view the Moon - many for the first time - through telescopes.
InOMN began last August as a celebration of the successful journey of NASA’s Lunar Reconnaissance Orbiter (LRO) around the Moon ( After the launch of LRO on June 18, 2009, Goddard's Education and Outreach Team hosted the event, "We're at the Moon!" The same day, the event "National Observe the Moon Night," was hosted at NASA's Ames Research Center (ARC) in Moffett Field, California by the Lunar Crater Observation and Sensing Satellite and NASA Lunar Science Institute (NLSI) teams. NLSI is based at NASA Ames. This year, both teams decided to expand the event by partnering with other NASA institutions, organizations and communities around the world.
Tonight the moon will be a waxing gibbous, about 82% of full. In the Tampa Bay area the Moon rises about 3:25 PM and sets about 2:40 AM.
Visit this link to find out more about International Observe the Moon Night:
...and visit this link to find observing locations in your area hosted by participating organizations.

Lunar Reconnaissance Orbiter (LRO)

Scientists think that on the moon humans will develop technologies to survive in the infinite frontier of space, because the moon presents the same challenges that humans will encounter throughout the universe: harmful radiation, electrified dust, and extreme temperatures.

Artist concept of the Lunar Reconnaissance Orbiter (LRO). Image Credit: NASA
Just as a scout finds the safest way for expeditions on Earth, NASA sent a robotic scout, called the Lunar Reconnaissance Orbiter (LRO), to gather crucial data on the lunar environment that will help astronauts prepare for long-duration lunar expeditions.
LRO will spend at least a year in a low polar orbit approximately 50 kilometers (31 miles) above the lunar surface, while its seven instruments find safe landing sites, locate potential resources, characterize the radiation environment and test new technology.
Learn more about LRO at the mission site:
More on the Moon
The moon is Earth's only natural satellite and the only astronomical body other than Earth ever visited by human beings. The moon is the brightest object in the night sky but gives off no light of its own. Instead, it reflects light from the sun. Like Earth and the rest of the solar system, the moon is about 4.6 billion years old.
The LRO imaging tools are busily mapping the Moon in 7 UV and visible wavelengths (320 nm through 689 nm). This color composite shows 320 nm light in blue, 415 nm in green and 689 nm in red, scene is ~1000 km wide. Credit: NASA/GSFC/Arizona State University

The moon is much smaller than Earth. The moon's average radius (distance from its center to its surface) is 1,079.6 miles (1,737.4 kilometers), about 27 percent of the radius of Earth.
The moon is also much less massive than Earth. The moon has a mass (amount of matter) of 8.10 x 1019 tons (7.35 x 1019 metric tons). Its mass in metric tons would be written out as 735 followed by 17 zeroes. Earth is about 81 times that massive. The moon's density (mass divided by volume) is about 3.34 grams per cubic centimeter, roughly 60 percent of Earth's density.
Because the moon has less mass than Earth, the force due to gravity at the lunar surface is only about 1/6 of that on Earth. Thus, a person standing on the moon would feel as if his or her weight had decreased by 5/6. And if that person dropped a rock, the rock would fall to the surface much more slowly than the same rock would fall to Earth.
Despite the moon's relatively weak gravitational force, the moon is close enough to Earth to produce tides in Earth's waters. The average distance from the center of Earth to the center of the moon is 238,897 miles (384,467 kilometers). That distance is growing -- but extremely slowly. The moon is moving away from Earth at a speed of about 1 1/2 inches (3.8 centimeters) per year.
The temperature at the lunar equator ranges from extremely low to extremely high -- from about -280 degrees F (-173 degrees C) at night to +260 degrees F (+127 degrees C) in the daytime. In some deep craters near the moon's poles, the temperature is always near -400 degrees F (-240 degrees C).
The moon has no life of any kind. Compared with Earth, it has changed little over billions of years. On the moon, the sky is black -- even during the day -- and the stars are always visible.
A person on Earth looking at the moon with the unaided eye can see light and dark areas on the lunar surface. The light areas are rugged, cratered highlands known as terrae (TEHR ee). The word terrae is Latin for lands. The highlands are the original crust of the moon, shattered and fragmented by the impact of meteoroids, asteroids, and comets. Many craters in the terrae exceed 25 miles (40 kilometers) in diameter. The largest is the South Pole-Aitken Basin, which is 1,550 miles (2,500 kilometers) in diameter.
The dark areas on the moon are known as maria (MAHR ee uh). The word maria is Latin for seas; its singular is mare (MAHR ee). The term comes from the smoothness of the dark areas and their resemblance to bodies of water. The maria are cratered landscapes that were partly flooded by lava when volcanoes erupted. The lava then froze, forming rock. Since that time, meteoroid impacts have created craters in the maria.
The moon has no substantial atmosphere, but small amounts of certain gases are present above the lunar surface. People sometimes refer to those gases as the lunar atmosphere. This "atmosphere" can also be called an exosphere, defined as a tenuous (low-density) zone of particles surrounding an airless body. Mercury and some asteroids also have an exosphere.
Learn more about our moon at these sites:
NASA’s Lunar Reconnaissance Orbiter (LRO) Mission:
Earth’s Moon - NASA’s Solar System Exploration site:

Moon - World Book at NASA: