No, not the silver-colored goo in thermometers... the planet!
Mercury, named for the swift-footed messenger of the Roman gods, is the planet closest to the Sun. It also happens to be the fastest-moving planet in our solar system, averaging about 30 miles per second as it makes its orbit around the Sun.
Of the five planest that can be seen with the naked eye, Mercury is typically considered to be the most difficult to see. Due to Mercury's close relative proximity to the Sun, the planet never strays too far from the Sun in our sky. Mercury is referred to as an "inferior planet", meaning its orbit is closer to the Sun than ours here on Earth. Because of that fact, Mercury always appears from our vantage point to be in the same general direction as the Sun.
The "elusive planet", as it is sometimes called, isn't really that hard to see. You just have to know when and where to look, and a window of opportunity for viewing Mercury in the evening sky is about to open up.
Where to look and when...
This evening (Wednesday, April 23), Mercury should be visible low in the west-northwest sky by about 30 minutes after sunset. In fact, at that time, Mercury will be the brightest object in the sky. It will look like a very bright star, with just a hint of a yellowish-orange tinge. If Mother Nature doesn't provide a clear sky for us this evening (and she certainly might not), don't worry! You'll have more opportunities to see Mercury in the coming days. By April 30th, Mercury will be "setting" as late as 85 minutes after the Sun.
As we head into the month of May, Mercury will slowly lose its brightness, but it will also slowly gain altitude in our sky. Let's hope for clear skies on the evening of May 6th, when the thin sliver of a 1.5-day-old crescent Moon will be sitting just a bit above and to the right of Mercury. By mid-May, the "elusive planet" will begin to go back into hiding. It's lowering altitude takes it back into the brighter sunset glow, rendering Mercury completely invisible by the final week of May.
Some fun Mercury facts...
- It takes the Earth 365 days (one year) to make its full journey around the Sun. Mercury makes the trip in only 88 Earth days.
- It takes the Earth 24 hours (one day) to make a full rotation on its axis. Mercury makes one full rotation in 59 Earth days! This results in very long, very hot "days", and very long, very cold "nights". Daytime temperatures can soar to nearly 900 degrees Fahrenheit -- that's hot enough to melt zinc and tin. The long darkness allows temperatures to drop to a frigid 300 degrees below zero! That gives Mercury the distinction of having the greatest temperature range of any planet in our solar system.(
- Because of the eccentric orbit of Mercury, someone standing on the surface of that planet might actually see the Sun reverse its course in the sky. At sunrise, this odd effect would make the Sun appear to rise above the horizon, then slow to a halt, then reverse direction and drop back below the horizon, and then rise again. Likewise, at sunset, the Sun would drop below the horizon, then pop back up into view before setting again for a second time within one Earth week.