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Phobos Photobombs Mars

16 Jul 2018, 15:30 UTC
Phobos Photobombs Mars
(200 words excerpt, click title or image to see full post)

Every two years or so, Mars and the Earth approach each other more closely than usual. We’re in no danger of colliding because both planets are kept in their orbits by the Sun’s gravity. But the orbital geometry gives us an opportunity to get a closer and brighter view of our nearest neighboring planet from our Earth-bound vantage point. The last time this happened was in 2016, and the next time is coming up later this month.
On May 12, 2016, a team of astronomers at the Space Telescope Science Institute used the Hubble Space Telescope (HST) to make several images of Mars close to the time of opposition. At that time, Mars was about 80 million km (50 million miles), or 0.53 AU, away from Earth with an apparent diameter of 18 arcseconds.
We used the Wide Field Camera 3 (WFC3) to make 25 exposures with the UVIS channel, using four filters in a sequence repeated three times. The exposures spanned about 40 minutes, about half of Hubble’s roughly 90 minute orbit. The times in the first graphic are in UT (Greenwich time) and the HST filter names are below each image (the central transmission wavelength in nanometers is ...

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