On August 27, 2003, Mars was the closest
its been to the Earth in the last 59,620 years. The distance separating
Earth and Mars on August 27, 2003, was 34.7 million miles or 0.37 AU (1
AU is the average distance between the Earth and Sun). The Earth
completes one orbit around the
Sun in 1 year or 365 days. But Mars is farther from the Sun and thus
the Sun's gravitational pull on Mars is weaker so it takes Mars longer,
1.9 years or 687
days, to orbit the Sun. This mean that every few years Earth catches up
to Mars and passes it just like a faster runner on an inner track
passes and
"laps" a slower runner on an outside track. On average, when Earth laps
Mars they are
separated by a distance of about 48.5 million miles or 0.52 AU.
However, because
the orbital paths of Mars and Earth are actually
ellitpical in shape, not perfectly circular, in some years the two
planets get significantly closer than average. Approximately every 15
years,
Earth and Mars get roughly as close as they did in August, 2003, when
they were separted by only 35 million miles.
On the night of its closest approach on August 27, 2003, Mars had an
apparent diameter of 25 arcsecond. For comparison, the full Moon has a
diameter of about half a degree, which is equal to 1800 arcsecond (1
degree = 3600 arcsecond). Because of
Mars' exceptional nearness, we could clearly see light/dark colored
terrain features
on Mars and the white ice cap on the South Pole of Mars, which is
composed mostly of frozen carbon dioxide rather than water, even with
the
smallest of the Observatory's telescopes. We
estimate that between 5,000 and 10,000 people saw Mars through the UCI
Observatory
telescopes that night! But we hope you come
and visit the UCI Observatory many times before the next close approach
in 2018, because there are
many other amazing things to see in the night sky on any given
night! For examples, take a look at some of our past Visitor Nights.
In Summer and Fall of 2006, the distance between Mars and
Earth will continue to grow
until it reachs a peak distance of 2.6 AU in early October, at which
time the distance will begin to decrease again. The next closest
approach between Earth and Mars will occur on Dec 19, 2007, when Mars
and Earth will be separated by 0.58 AU. Then Mars will be about 60%
farther than it was on its spectacular close approach in August 27,
2003, and its apparent diameter will be 15 arcseconds, but will still
be a fabulous event and we plan to hold a Visitor Night at the UCI
Observatory near that date. If you want us to add your email address
to our email list so you receive notices of upcoming Visitor Nights,
please send an email to tsmecker@uci.edu.