Lunar, Solar Eclipses Hold Secrets to Other Worlds
Written by Anne Minard
Want to know about the atmospheres of planets around other stars, and the stars themselves?
Start at home.
A pair of papers in this week's issue of Nature is advocating continued studies of both lunar eclipses, when the Moon transits Earth's shadow, and solar eclipses — when the Moon comes directly between Earth and the sun.
NASA eclipse diagram
Enric Palle, of the Spanish Instituto de Astrofisica de Canarias, and his co-authors point out in one of the papers that of the 342 planets known to be orbiting other stars, 58 ‘transit’ the stellar disk, meaning that they can be detected through a periodic decrease in the flux of starlight.
"The light from the star passes through the atmosphere of the planet, and in a few cases the basic atmospheric composition of the planet can be estimated," they write. To calibrate our abilities to study those other atmospheres, it's best to practice on Earth, they propose.
The team utilized the optical and near-infrared transmission spectrum of the Earth, obtained during a lunar eclipse. The technique is different from another common practice: observing the earthshine, or the light reflected from the dark side of the Moon.
"Some biologically relevant atmospheric features that are weak in the reflection spectrum (such as ozone, molecular oxygen, water, carbon dioxide and methane) are much stronger in the transmission spectrum, and indeed stronger than predicted by modelling," Palle and his co-authors write. "We also find the ‘fingerprints’ of the Earth’s ionosphere and of the major atmospheric constituent, molecular nitrogen (N2), which are missing in the reflection spectrum."
"Thus, the transmission spectrum can provide much more information about the atmospheric composition of a rocky planet than the reflection spectrum can."
Solar eclipse. Credit: NASA
In the second paper, author Jay Pasachoff, who splits his time between Caltech and Williams College, in Massachusetts, reviewed a wealth of knowledge gleaned from solar eclipses.
"Observations of the Sun during total eclipses have led to major discoveries, such as the existence of helium (from its spectrum), the high temperature of the corona (though the reason for the high temperature remains controversial), and the role of magnetic fields in injecting energy into—and trapping ionized gases within—stellar atmospheres," he writes.
Pasachoff notes that there's no real end in sight for the usefulness of solar eclipses: "The Moon is receding from the Sun sufficiently slowly that our descendants on Earth will be able to see total eclipses for over 600 million years."
But he predicts an eventual transition from ground-based to space solar telescopes, especially for getting at tantalizing solar mysteries like the nature of coronal heating.
"At present the paired science and beauty of solar eclipses remain uniquely available to scientists and others in the path of totality."
Source: Nature
Filed under: Astronomy, Eclipses
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June 10th, 2009 at 1:26 pm
"The Moon is receding from the Sun" ??
Indeed?
Whose typo is that? ;-D
June 10th, 2009 at 5:17 pm
The research on rendering lunar eclipses can be found here: http://www.cs.rpi.edu/research/groups/graphics/eclipse_gi09/gi2009.pdf (This is a beautifully done short paper, but it is a 22Mb PDF file-well worth a look!).
June 10th, 2009 at 5:41 pm
Another beautiful presentation of the lunar eclipse rendering project can be found here: http://www.cs.rpi.edu/research/groups/graphics/eclipse_gi09/presentation.pdf .This mostly graphic presentation has some awesome prediction-observation sequences. The researchers note that their prediction of the upcoming 2010 lunar eclipse may be in error due to the unforseen eruption of that Alaskan volcano. Maybe these atmospheric fluctuations can be more accurately modeled in the future.
June 12th, 2009 at 9:50 am
Sweet.