Q&A: Do We Have any Pictures Taken of The Moon in Front of Earth?
We Do! :) They’re rare, though, because most satellites orbiting the Earth, orbit from between low Earth-orbit (LEO), which is about 300 km above the surface of the Earth, to geosynchronous orbit, which is about 36,000 km above the surface… and a few in a little past this, in high Earth-orbit (HEO).
The moon, however, is about 10 x this distance at (on average) ~384,000 km away from the Earth.
The image above shows a scale image of the Earth, and the common orbits around it. The top portion shows the LEO in blue, extending to about 2,000 km above the Earth, in green the medium Earth-orbit (2,000 km — 35,786 km), and beyond that the HEO begins in red.
The bottom portion of the image shows a view of these same orbits, zoomed out to show the relative distance of the Earth and the Moon. As the distance extends further out, there are fewer useful reasons to launch satellites this far, and eventually you would run into complications of the moon’s gravity making their orbit around the Earth unstable, so there are no satellites orbiting much past the halfway point between the Earth and Moon.
Of course, a camera (satellite) would have to be past the moon, in order to look at the Earth, and see the moon in front of it.
There are a few satellites which travel within the “Lagrange points”, which are stable orbit locations that do not require orbiting around the Earth. They instead orbit the Sun once per year, keeping pace with the Earth, and the Earth’s gravity provides a tug to keep them stable.
L1 and L2 are about 1.5 million km away from the Earth, which is a good distance beyond the moon, and the L3, L4, and L5 Lagrange points are located along the orbital path that the Earth follows around the sun, They are much further away than the first two Lagrange points, and much, much further away than low, medium, and high Earth-orbits.
The National Oceanic and Atmospheric Administration’s Deep Space Climate Observatory (DSCOVR), launched in Feb of 2015 is “parked” at the L1 Lagrange point, between the Sun and the Earth-moon system. This means that one side of it always faces the sun, and the other side always faces the Earth-Moon system. It recently gave us this incredibly beautiful photo of the moon transiting in front of the Earth:
Here is a sequence of images from the same above DSCOVR photo-shoot, showing the moon transiting across the Earth over a period of several days:
Video of the moon transiting the Earth taken by the DSCOVR spacecraft
The Lagrange L1 point is particularly useful for satellites which observe the sun, and other probes currently in operation there include the ESA/NASA’s Solar and Heliospheric Observatory (SOHO), which studies the sun and has found and cataloged more than 3,000 comets, and NASA’s Advanced Composition Explorer (ACE), which examines energetic particles from the solar wind and the interplanetary medium.
The opposite point, the Lagrange L2, is a million and a half kilometers on the far side of the Earth from the sun, and is always within the shadow of the Earth. This spot is ideal for deep-space observatories, such as the upcoming James Webb Space Telescope(JWST), which will be the successor of the Hubble Telescope, and is currently scheduled for launch March 2021 (although it keeps getting delayed, unfortunately). The JWST will be looking at the farthest, and dimmest galaxies we’ve ever been able to see, and having the Earth between it and the sun, will keep the telescope from being blinded by the Sun, allowing it to see back to the earliest times in our Universe that we have ever peered at.
Other important probes we’ve put in the L2 point, are the ESA’s ongoing GAIA Spacecraft, which is constructing the largest 3D catalog of astronomical objects ever made (stars, planets, comets, asteroids and quasars, among other objects), and NASA’s (now decommissioned) Wilkinson Microwave Anisotropy Probe, which detected the long theorized background microwave radiation, which was an “echo” of the initial expansion of the Universe, and a predicted evidence of the Big Bang theory.
Originally published at news4starstuffs.com on October 4, 2018.
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