Huh… eight nights of Chanukah, and eight planets in the solar system. Whaddya know? Okay… for the first night of Chanukah, here are eight facts about the first planet. Some you might know, some you might not:
1) Mercury is the eighth largest planet (okay, also known as the smallest) in the solar system, but only the eleventh largest thing in the solar system. Jupiter’s moon Ganymede, and Saturn’s moon Titan are bigger.
2) Until the 1960s, it was thought that Mercury always kept the same face toward the Sun, which would make its day the same length as its year. This is similar to the Moon always keeping the same face toward the Earth. In reality, Mercury rotates three times for every two times it revolves. It’s day is two-third the length of its year.
3) Because it’s so close to the Sun, and travels so quickly in its orbit, so far only two probes have explored Mercury: Mariner 10 starting in 1974; and MESSENGER starting in 2008.
4) Mercury’s axis is almost perfectly vertical relative to its orbital plane, so it has no seasons. By contrast, the Earth is tilted 23.5 degrees relative to its orbit.
5) Even though Mercury has the widest temperature swings anywhere in the solar system, over 1000 degrees Fahrenheit, there is water ice on its surface. MESSENGER photographed ice at the bottom of craters in areas that are always in shadow, and are very cold.
6) Since Mercury is so close to the Sun, it always appears close to the Sun in the earth’s sky, and always rises and sets within two hours of the Sun, though this is often even shorter.
7) Most of the craters on Mercury are named after artists, composers, and writers.
8) Since it’s between the Earth and Sun, Mercury is one of three objects that appear to go through phases as seen from the Earth. The Moon and Venus are the others.