For the first time in more than a decade, Mercury, Mars, Venus, Saturn, and Jupiter — the five planets bright enough to be seen with an unaided eye — will all be visible at once in the sky.
You'll have to wake up early to catch it. Starting January 20, it will be possible to see all five planets in a row, about 45 minutes before sunrise, Sky and Telescope reports. The planets should be visible in this arrangement until February 20.
Five planets line up in the A.M. sky for 1st time in a decade - https://t.co/Fi2aUrDUsn #astronomy #skywatching pic.twitter.com/3rbDhbJ7hO— Scott Sutherland (@ScottWx_TWN) January 19, 2016
(Sky and Telescope notes it might get harder to see Mercury after the first week of February, because of its low position near the horizon).
This is the first time five planets have been aligned in a night sky since January 2005.
Mercury will appear lowest to the horizon, and its faint light will be hardest to spot in the southeastern sky (in the Northern Hemisphere). Then, from left to right (from southeast to southwest), you'll be able to see Venus, Saturn, Mars, and Jupiter, in a line that roughly traces the path the sun will take through the day.
Because the planets orbit on a very similar plane as Earth does around the sun, they appear lined up in the sky.
You may be able to identify Venus first, as it will be the brightest object in the array (the only brighter objects in the sky overall are the sun and the moon). The five planets will cover a large swath of sky, so to view them all at once you'll need to either be up high or have a view unobstructed by trees or buildings.
The alignment has no astronomical significance other than that it is rare — a coincidence that the five planets with their varying speeds and orbits appear in the same field of view. But it is cool nonetheless.