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Earth and Moon From an Alien's Perspective
krygny writes "NASA's Deep Impact spacecraft (whose extended mission is called EPOXI) has created a video of the moon transiting Earth as seen from 31 million miles away. Scientists are using the video to develop techniques to study alien worlds. 'Our video shows some specific features that are important for observations of Earth-like planets orbiting other stars,' said Drake Deming of NASA's Goddard Space Flight Center... 'A "sun glint'" can be seen in the movie, caused by light reflected from Earth's oceans, and similar glints to be observed from extrasolar planets could indicate alien oceans. Also, we used infrared light instead of the normal red light to make the color composite images, and that makes the land masses much more visible.'" Here are links to the two videos, one red-green-blue and the other infrared-green-blue.
The importance isn't the image itself. It's how the image changes with time, including the rotation of the earth changes the reflected light and the position of the moon.
There are certain things we can guess, but in trying to build a model of how to observe other Earth-like planets from a distance, an actual observation, even from a much shorter distance, can improve the technology many times over.
In the end, when we look for extra-solar planets, we aren't looking for pretty images, we're looking for funny effects that are observable from a nearly singular point of light: regular variances in intensity, spectrum, polarization, etc..
Likewise, if someday we could do a similar study from one of our probes that's managed to get out of the solar system, that would improve the model another order of magnitude, accounting for other variables in the observation.
.mov is QuickTime, which is old and not proprietary; I have a book here describing the format. However, that's just the container format; it's the codecs commonly used within QT these days that are proprietary.
And according to mplayer, the codecs used here are mp4v for video, and aac for audio. In other words, (tada!) MPEG.
You can't resolve objects at the separation of the moon and earth from 30 trillion miles away. ... By studying star wobbles an astronomer might infer the presence and mass of a "planet," but that won't tell him if it's really a single planet or a planet-moon system.
Sure you can. There is a lot more information in one pixel than meets the eye. That one pixel of a star can show you the size, mass, and semi-major axis of a planet (though current technology is only sensitive enough to be able to detect large planets orbiting very closely to their stars). What you do is observe how the star wobbles about its center of mass due to a planet (via redshift) and if the planet transits across the star. These same techniques could be used with a planet with a moon if you could see it. One pixel is enough.
>>You think things have changed much in 12 years?
>Yes. They've gotten much worse.
Maybe the big picture is worse, but I note that incoming freshmen at the university where I work, are
coming in quite strong with physics, chemistry, calculus, writing, and most even have good placement in
a second language. My local, small, unscientific sample indicates a strong high school system, turning
out students who are as well-prepared for university as we could ask for.
Are you seeing different results among graduating seniors?
-fb Everything not expressly forbidden is now mandatory.
VLC will play them.
I am very small, utmostly microscopic.
Sound is a pressure wave...so yeah, it is loud near the Sun. This was discussed on The Universe (History Channel).
Bill Clinton: Pimp we can believe in. - The Shirt!!!
The entire length of the video represents a day on Earth, and since the Earth is about quarter wrt the spacecraft, the video would have to represent about six more days before it would even be possible of the lunar shadow to appear on the Earth (btw, that's a solar eclipse, not lunar). They also have to be perfectly aligned, which would be difficult to judge from a cursory glance at the video. There was no eclipse during May when this video was taken, but there is going to be one on August 1.
Total Solar Eclipse
It seems that the moon doesn't orbit the earth around the equatorial plane but rather the ecliptic. There's a description here and a nice diagram showing the planes here
Hi, ScienceTim here, from the EPOXI team. Let me correct some misconceptions. The purpose of this experiment is to make a measurement of the Earth's spectrum at low spectroscopic resolution that allows us to simulate what an observer would detect from outside the solar system. Although we have spatial resolution in this movie, our scientific results will be obtained by adding up all the light in each of our filters in order to explore the ability to deduce properties of the Earth in unresolved data (we actually have 7 filters, not just the 4 that we show, plus a near-IR spectrometer). This information can be used to evaluate the engineering requirements for future space missions that will have the actual purpose of detecting and characterizing extrasolar terrestrial planets. Such a mission will be able to collect very few photons, so it will be required to do its job with very limited information. Why not just simulate the Earth computationally, since we know a great deal about it? We do this, of course. Converting our detailed knowledge into an accurate simulation is not straightforward, however. Radiative-transfer techniques employ a variety of approximations, depending on the situation, and those approximations may require us to know something that would not be available for an actual extrasolar planet -- as an easy example, the pressure scale height is important for some methods. The EPOXI observation, and others like it that we acquired on earlier and later dates, provide an empirical test for those models. Once we have an empirically-tested model verified, we can apply the techniques from that model to the problem of modeling the apparent spectrum of nearly-Earthlike and not-at-all Earthlike terrestrial planets. Keep in mind that this measurement is an interesting and useful exercise in the value of empirical test, but it is not the primary mission element. Currently, the primary mission element is observations of stars with known planets, to investigate these systems more deeply. We will finish in another month or so. Then we cruise for about a year, then we have a close flyby of another comet, after which the mission will be over. We have lots of good stuff coming.
The Earth's axis is tilted 23 degrees from the plane of its orbit. The Moon's orbit is much closer to the same plane as the Earth-Moon orbit of the Sun.
Hmm. PhD in Physics. Not *too* far over my head, I think. I can always be wrong (astrophysics wasn't my specialty), but I actually think it *is* a bold claim. When you extrapolate (note, not interpolate) *anything* by several orders of magnitude, you better be sure of your deductions.
Radiant energy intensity falls off with the square of the distance. Variation within that intensity therefore falls off at the same rate, and is consequently harder to detect above the noise threshold - with the relative distances we're talking about here, that noise threshold is looking scarily close...
Let's say there's a civilisation on Gamma Cephei (about 50 light years distant). Even if we just take into account the inverse-square law, the signal:noise ratio on Gamma Cephei is 27,808,132,115 *times* worse than the (already poor) signal:noise ratio of the reported experiment. Now toss in scattering due to space-born dust/whatever, red-shift effects, any interference effects, any gravitational effects, and it starts to look just a *little* bit harder, don't you think ?
Simon
Physicists get Hadrons!
http://epoxi.umd.edu/4gallery/Earth-Moon_vid.shtml You can view the animated gifs in your browser.