The Hubble Space Telescope captured this photo of Mars on May 12, 2016 when the planet was 50 million miles from Earth. Image credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), J. Bell (ASU), and M. Wolff (Space Science Institute)
Early Sunday morning, just after midnight (local time), Mars will be as close to Earth as it's been in years, and nearly as bright as Jupiter. How big and bright will it be? If you own a half-decent telescope and know how to use it, you'll be able to see surface features, including polar caps, clouds, and mountains—that is, with a little help from Sky & Telescope's map of Mars or NASA's (below). With that kind of clarity, you might be able to spot Mark Watney. So what's going on up there?
OPPOSITION LEADS TO LOTS OF LIGHT
When a celestial body is, relative to Earth, directly opposite the Sun (i.e. Sun—Earth—object), it is "in opposition." This means that from the perspective of Earth, the body will be receiving the Sun's full illumination, and will thus appear brighter than usual. As you might intuit, a body in opposition implies a nearer proximity in orbit (though not necessarily nearest). Closer, as it relates to what we see in the sky, means bigger. Just how big varies, however.
Planets have elliptical orbits as opposed to circular ones, and "orbital eccentricity"—elliptical-ness, so to speak—differs from planet to planet. Mars is pretty eccentric; Earth not so much. Mars and Earth also revolve around the Sun at different speeds. It takes Mars 687 days to complete an orbit. It takes us 365 days. The difference in speed and orbital eccentricity of Earth and Mars means the point around the Sun at which we "meet" varies. Sometimes our closest is when Mars is far from the Sun on its elliptical orbit. Sometimes—as we're experiencing this year—it is when Mars is nearer to the Sun (or near "perihelion"). The upshot is that this year, Mars will be bigger and brighter in the dark sky than it's been in over a decade.
NASA's Scientific Visualization Studio
CLOSEST APPROACH CAPTURED BY HUBBLE FOR 20+ YEARS
As Mars comes into opposition, astronomers are taking the occasion to study changes in the Martian landscape. On May 12, for example, the Hubble Space Telescope used its Wide Field Camera 3 instrument to capture images of Mars that reveal geologic features as small as 19 miles across. This is not the first time Hubble has captured Mars in opposition, and each time since 1995, the telescope has captured different angles and ranges, providing scientists new data sets from which to unlock the mysteries of the Red Planet.
NASA, ESA, and Z. Levay (STScI)
Though Mars is in opposition on Sunday morning, Martians will probably wait until May 30 to fire their cannons at Earth, as that is when the two planets reach their closest proximity. If weather does not cooperate where you are, do not fret: Mars and Earth be even closer in 2018, and you can plan to catch the show then.