Tuesday, July 04, 2017

I Can Name That Eclipse in Five Notes

Total solar eclipses have always captivated our attention. They have even made their way into our music. See how many of these songs you recognize.

March 7, 1970 total solar eclipse. Image Credit: NSO/AURA/NSF


You’re So Vain, composed and performed by Carly Simon

. . . you flew your Lear jet up to Nova Scotia
To see a total eclipse of the sun

This is the only known recorded song with lyrics that mention a specific eclipse. But which one? The recording was released November 1972. And Nova Scotia had recently experienced two total solar eclipses, one on March 7, 1970 and another on July 10, 1972. Simon has reported that she wrote the song in 1971. If Simon was reflecting on recent events, then she probably meant the total solar eclipse of March 7, 1970.

Eclipse, by Pink Floyd from ‘Dark side of the Moon’

… and everything under the sun is in tune
but the sun is eclipsed by the moon.

Total Eclipse of the Heart, sung by  Bonnie Tyler.

…Once upon a time there was light in my life
But now there's only love in the dark
Nothing I can say
A total eclipse of the heart…

If we go farther back in time, we come across a smattering of sheet music published in the 1800s and early-1900s.

The Total Eclipse Gallop, composed by E. Mack and published in 1919 by Lee & Walker. This song commemorates the August 7, 1869 total solar eclipse, which was visible across the continental United States.

Eclipse, composed by Herman Darewski (1883-1947) was published in 1919.

Other memorable dance tunes that are now long forgotten include:

Eclipse March, 1899 published by Troedel & Co., National Library of Australia.

Eclipse Polka,  by Giuseppe Bistolfi. Published by Kansas City, MO: J.W. Jenkins Son, 1889. 

University of Missouri, Kansas City Sheet Music Collection

Eclipse Polka, 1853, Published by Wm. Vanderbeek and Son,

Eclipse Waltz, 1854, W. C. Peters and Sons

Eclipse Polka, 1874, Lee & Walker

Eclipse Quickstep, 1885, Richards, J. G

Eclipse Gallop, 1885, Spear & Dehnhoff

Eclipse Schottische, 1884, Stewart, S. S.


For more information on the August 21 total eclipse, and eclipses in general, visit:



 -

Monday, July 03, 2017

Solar Viewing Safety

When it comes to looking at the sun, safety comes first! Here are some important questions and answers about solar viewing safety.

Anatomy of the Human Eye. Image Credit: NASA

Why is it not safe to look at the sun even when only a small part of it is visible?

The rods and cones in the human retina are very sensitive to light. Even a thin sliver of the sun’s disk covers thousands of these light-sensitive cells. Normally during daylight conditions, the iris contracts so that only a small amount of light passes through the lens and then reaches the retina. This level of indirect sunlight is perfectly OK and the eye has evolved over millions of years to safely see the daylight world under most circumstances. The problem is that the sun’s surface is so bright that if you stare at any portion of it, no matter how small, it produces enough light to damage individual retinal cells.  It takes a few seconds for this to happen, but afterwards you will see a spot as big as the solar surface you glimpsed when you look away from the sun at some other scenery. Depending on how long you gazed at the sun and how badly the retinal cells were damaged,  this spot will either fade away in time or remain permanent.  You should never assume that you can look away quickly enough to avoid eye damage because every person is different in terms of their retinal sensitivity, and you do not want to risk being the one who damages their eyes just to try to look at the sun. If you want to see what the sun looks like, use a properly-equipped telescope. Or just go online and view thousands of pictures taken of the sun by telescopes and NASA spacecraft.

Is it true that you should not look at the sun even during a total solar eclipse?

There is a misunderstanding being circulated that during a total solar eclipse when the moon has fully blocked the light from the sun, that there are still harmful ‘rays’ that can injure your eyes.  This is completely false. When the bright photosphere (the visible surface) of the sun is completely covered, only the faint light from the corona is visible, and this radiation is too weak to have any harmful effects on the human retina.

The misunderstanding comes about because of using the general term ‘solar eclipse’ to describe both the total phase when the sun disk is completely blocked, and the minutes before and after totality when there is still some of the sun’s disk visible. It is harmful to view even a sliver of the sun disk because of its intensity, and so to simply say that you should not view a solar eclipse is rather inaccurate.

Do lunar and solar eclipses have any noticeable effect on humans?

There is no evidence that eclipses have any physical effect on humans. However, eclipses have always been capable of producing profound psychological effects. For millennia, solar eclipses have been interpreted as portents of doom by virtually every known civilization. These have stimulated responses that run the gamut from human sacrifices to feelings of awe and bewilderment. Although there are no direct physical effects involving known forces, the consequences of the induced human psychological states have indeed led to physical effects.

How are eyes damaged by staring at the sun?

Solar retinopathy is a result of too much ultraviolet light flooding the retina. In extreme cases this can cause blindness, but is so painful that it is rare for someone to be able to stare at the sun for that long. Typically, eye damage from staring at the sun results in blurred vision, dark or yellow spots, pain in bright light or loss of vision in the center of the eye (the fovea). Permanent damage to the retina has been shown to occur in approximately 100 seconds, but the exact time before damage occurs will vary with the intensity of the sun on a particular day  and with how much the viewer's pupil is dilated  from decongestants and other drugs they may be taking.  Even when 99% of the Sun's surface (the photosphere) is obscured during the partial phases of a solar eclipse, the remaining crescent Sun is still intense enough to cause a retinal burn. Note, there are no pain receptors in the retina so your retina can be damaged even before you realize it, and by then it is too late to save your vision!

Where can I get the right kind of solar filter to view the eclipse?

Many people will obtain eclipse viewing glasses. To date, three manufacturers have certified that their eclipse glasses and hand-held solar viewers meet the ISO 12312-2 international standard for such products: Rainbow Symphony, American Paper Optics, and Thousand Oaks Optical. These companies may be found online and the glasses ordered, but you really need to order your glasses many months in advance because of the anticipated huge audience that could number in the hundreds of millions. If you are a photographer or amateur astronomer, you will want professional-grade solar filters to cover your binoculars, telescope or camera. Companies like Thousand Oaks Optical and others you can find by using the keyword ‘Solar filters’ have these filters for sale, but again due to the large number of likely customers along the path of totality, you need to order your filter many months in advance. You will also need some time to learn how to use the filter with your optical system, and if you are photographing the eclipse, take lots of test shots to get the right solar disk size and sharpness.

Is it only the bright light that is dangerous when viewing the sun?

Actually, although filters and glasses do safely block the intense sunlight that is known to damage retinas, the infrared ‘heat’ from the sun can also make viewing uncomfortable as it literally warms the eye.  This is why staring at the sun for minutes at a time even with proper filters can still over-heat the tissues and fluids in the eye, and the consequences of this heating can be dangerous as well. To avoid this problem before totality takes place, try not to use your filters without frequently looking-away to cool your eyes. During totality, there is no adverse heating of the eyeball since the solar disk is not visible.

Isn’t this ‘safety’ issue about eclipse viewing, a bit overblown?

Absolutely not!  You cannot look at the sun without suffering severe damage. We have many built-in reflexes to prevent this. The ONLY exception is in viewing solar eclipses. It is an inherently dangerous activity that you have to do very carefully in order not to suffer eye damage. There are specific steps you can take, based on the experience of  thousands of professionals, not only in astronomy but in medicine. So, bottom line: read the safety warnings and make sure you understand how to view the eclipse before  August 21, so that the only lasting impression you have is a wonderful memory of the event, not a damaged retina!

For more information on the eclipse, and how to safely view it, visit:



 -

Thursday, June 29, 2017

The Sun, a Primer

The Sun is a huge, glowing ball at the center of our solar system. The sun provides light, heat, and other energy to Earth. The sun is made up entirely of gas. Most of it is a type of gas that is sensitive to magnetism. This sensitivity makes this type of gas so special that scientists sometimes give it a special name: plasma. The planets and their moons, dwarf planets, tens of thousands of asteroids, and trillions of comets revolve around the sun. The sun and all these objects are in the solar system. Earth travels around the sun at an average distance of about 92,960,000 miles (149,600,000 kilometers) from it.

An Extreme Ultraviolet Imaging Telescope (EIT) image of the Sun and a huge, handle-shaped prominence, taken on September 14,1999, in the 304 angstrom wavelength. Prominences are huge clouds of relatively cool dense plasma suspended in the Sun's hot, thin corona. At times, they can erupt, escaping the Sun's atmosphere. Image credit: NASA/European Space Agency

The sun's radius (distance from its center to its surface) is about 432,000 miles (695,500 kilometers), approximately 109 times Earth's radius. The following example may help you picture the relative sizes of the sun and Earth and the distance between them: Suppose the radius of Earth were the width of an ordinary paper clip. The radius of the sun would be roughly the height of a desk, and the sun would be about 100 paces from Earth.

The part of the sun that we see has a temperature of about 5500 degrees C (10,000 degrees F). Astronomers measure star temperatures in a metric unit called the Kelvin (abbreviated K). One Kelvin equals exactly 1 Celsius degree (1.8 Fahrenheit degree), but the Kelvin and Celsius scales begin at different points. The Kelvin scale stars at absolute zero, which is -273.15 degrees C (-459.67 degrees F). Thus, the temperature of the solar surface is about 5800 K. Temperatures in the Sun's core reach over 15,000,000 K (27,000,000 degrees F).

The energy of the sun comes from nuclear fusion reactions that occur deep inside the sun's core. In a fusion reaction, two atomic nuclei join together, creating a new nucleus. Fusion produces energy by converting nuclear matter into energy.

The sun, like Earth, is magnetic. Scientists describe the magnetism of an object in terms of a magnetic field. This is a region that includes all the space occupied by the object and much of the surrounding space. Physicists define a magnetic field as the region in which a magnetic force could be detected—as with a compass. Physicists describe how magnetic an object is in terms of field strength. This is a measure of the force that the field would exert on a magnetic object, such as a compass needle. The typical strength of the sun's field is only about twice that of Earth's field.

But the sun's magnetic field becomes highly concentrated in small regions, with strengths up to 3,000 times as great as the typical strength. These regions shape solar matter to create a variety of features on the sun's surface and in its atmosphere, the part that we can see. These features range from relatively cool, dark structures known as sunspots to spectacular eruptions called flares and coronal mass ejections.

Flares are the most violent eruptions in the solar system. Coronal mass ejections, though less violent than flares, involve a tremendous mass (amount of matter). A single ejection can spew approximately 20 billion tons (18 billion metric tons) of matter into space. A cube of lead 3/4 mile (1.2 kilometers) on a side would have about the same mass.

The sun was born about 4.6 billion years ago. It has enough nuclear fuel to remain much as it is for another 5 billion years. Then it will grow to become a type of star called a red giant. Later in the sun's life, it will cast off its outer layers. The remaining core will collapse to become an object called a white dwarf, and will slowly fade. The sun will enter its final phase as a faint, cool object sometimes called a black dwarf.

To be continued...

-

Wednesday, June 28, 2017

Are You an Umbraphile? You May Be After August 21!

um-bra-phile (ˈəm-brə-ˌfī(-ə)l) noun. 1. an avid observer of, or a person with a great interest in, eclipses. [from Latin umbra ‘shade’ and Greek philos ‘loving’]

An umbraphile is, literally, a "shadow lover." He or she is addicted to total solar eclipses. Those who have not stood in the moon’s shadow may not understand. But those who have, do. For many umbraphiles, it is way of life. These are the “solar eclipse chasers.” Once every 16 months, on average, umbraphiles drop what they are doing and travel, by whatever means necessary, to gather along a narrow strip in some remote corner of the globe defined by the laws of celestial mechanics.

The next total solar eclipse will occur August 21, crossing the continental United States from coast to coast. Are you an umbraphile? If you aren't, you may be very soon!

-

Tuesday, June 27, 2017

Have You Made Your Reservations for the August 21 Total Solar Eclipse?

There are less than two months until the August 21 total solar eclipse. The path of totality will pass from coast to coast across the entire continental United States. The path of totality is about 70 miles wide. So, there are lots of great places in the U.S. you can see the event.

The Path of Totality for the August 21, 2017 Total Solar Eclipse. Image Credit: NASA

If you are coming from outside the path of totality and hope to stay overnight within the path August 20, before the August 21 event, you should make your plans now if you have not done so already. Hotels are filing up fast, and are already filled up in some locations.

Please do not wing this! The Department of Transportation is asking that people DO NOT pull off to the side of the interstate. Visit the DoT website where you can see how traffic may be affected by the eclipse. Visit the Fact Sheet link below.

2017 Solar Eclipse Transportation Fact Sheet for State and Local Departments of Transportation

Here are the states through which the center line of the path of totality will pass.

  • Oregon
  • Idaho
  • Wyoming
  • Nebraska
  • Kansas
  • Missouri
  • Kentucky
  • Tennessee
  • Georgia
  • South Carolina


To get more of an idea of the location of the path of totality, check out this list of major cities that will be in the path.

  • Corvallis, Albany and Lebanon, Oregon
  • Idaho Falls, Idaho
  • Casper, Wyoming
  • Grand Island, Lincoln Nebraska
  • St Joseph, Missouri
  • Kansas City, Kansas
  • St Louis, Missouri
  • Bowling Green, Kentucky
  • Nashville, Tennessee
  • Greenville, South Carolina
  • Columbia, South Carolina


The website Eclipse2017.org has a great page to see what cities will be in the path and how long totality will last at those locations. Follow the link below.

Cities that lie in the Path of Totality

-

Sunday, June 25, 2017

Make a Pinhole Camera to View the Solar Eclipse

Pinhole Camera

You don't need a lot of money to observe a solar eclipse in complete safety. With just a few simple supplies, you can make a pinhole camera that lets you watch a solar eclipse safely and easily from anywhere. 

A pinhole camera is a simple camera without a lens. Instead of a lens, it has a tiny aperture, a pinhole. Light from a scene passes through the aperture and projects an inverted image, which is known as the camera obscura effect.

Remember: You should never look at the sun directly without equipment that's specifically designed for looking at the sun. Even using binoculars or a telescope, you could severely damage your eyes or even go blind! The totality portion of a solar eclipse is safe. But looking at anything as bright as the sun is NOT safe without proper protection. And no, sunglasses do NOT count. 

Now, let's make a pinhole camera! You will need the following materials.
  • 2 pieces of white card stock
  • 1 piece of unused, smooth, aluminum foil
  • 1 pair of scissors
  • 1 roll of tape
  • 1 pin or paper clip

Image Credit: NASA/JPL-Caltech


1. Cut a square hole into the middle of one of your pieces of card stock.
Image Credit: NASA/JPL-Caltech


2. Tape a piece of aluminum foil over the hole.
Image Credit: NASA/JPL-Caltech


3. Use your pin or paper clip to poke a small hole in the aluminum foil.
Image Credit: NASA/JPL-Caltech


4. Place your second piece of card stock on the ground and hold the piece with aluminum foil above it (foil facing up). Stand with the sun behind you and view the projected image on the card stock below! The farther away you hold your camera, the bigger your projected image will be.

To make your projection a bit more defined, try putting the bottom piece of card stock in a shadowed area while you hold the other piece in the sunlight.
Image Credit: NASA/JPL-Caltech


5. For extra fun, try poking multiple holes in your foil, making shapes, patterns and other designs. Each hole you create will turn into its own projection of the eclipse, making for some neat effects. Grab a helper to take photos of your designs for a stellar art project you can enjoy even after the eclipse has ended. 
Image Credit: NASA/JPL-Caltech

-

Saturday, June 24, 2017

Ugarit Total Solar Eclipse

Trivia: The Ugarit Total Solar Eclipse

In 1948, a clay tablet was discovered in the port city of Ugarit in Northern Syria. In the text of the tablet, a Mesopotamian historian noted, "On the day of the new moon, in the month of Hiyar, the sun was put to shame, and went down in the daytime, with Mars in attendance." Scientists realized the text described a total solar eclipse in which the planet Mars was visible during totality.

Researchers originally dated the eclipse event as May 3, 1375 B.C. But further study suggested a different eclipse. Researchers considered the dating of the tablet, combined with the text's statement of the month in which the eclipse occurred and the fact that Mars was seen during totality. This evidence pointed to the total eclipse of March 5, 1223 B.C. The revised findings were first published in 1989 in the journal Nature.

The Ugarit eclipse is one of the earliest solar eclipses recorded. The path of totality began in the Atlantic Ocean, crossed north-western Afrca, Turkey, and central Asia.

The Accelerating Moon, the Decelerating Earth

The dating of ancient solar eclipses provides astronomers with reference points to determine long-term evolution of angular momentum in the Earth-Moon system--that is, it helps astronomers understand how the moon's orbit and Earth's rotation have changed over time. The revised date--March 5, 1223 B.C.--implies that the secular deceleration of Earth's rotation has changed very little during the past 3,000 years.

Secular What?

Ocean tides are caused by the gravitational pull of the moon (and, to a lesser extent, the Sun). The resulting tidal bulge in Earth's oceans is dragged ahead of the moon in its orbit due to the daily rotation of Earth. As a consequence, the ocean mass offset from the Earth-Moon line exerts a pull on the moon and accelerates it in its orbit. Conversely, the moon's gravitational tug on this mass exerts a torque that decelerates the rotation of Earth. The length of the day gradually increases as energy is transferred from Earth to the moon, causing the lunar orbit and period of revolution about Earth to increase.

You can learn more about secular acceleration from the following NASA article.

-