Another week (and year, for that matter) , which means a new featured sight in the sky. This week, the focus is on two outer planets that will be having their third close encounter within a year’s time.
Throughout much of last year, two of the outer planets have been in an on-again, off-again dance: Jupiter and Uranus. This week, specifically on Tuesday, the year long tango will come to its climax as the planets make their third and final close approach of the year, coming to within a half degree of each other.
To understand why two outer planets can come this close together not one but three times in a single year requires some knowledge of planetary motion. When observed over the course of a year, planets appear to move forward with the stars most of the time. However, for a period of time, the superior planets (those outside Earth’s orbit), go through what is called retrograde motion, which is when a planet appears to slow, stop, reverse course, stop again, and then continue on a forward course. It was this inexplicable motion that got the word planet (Greek for wanderer) attached to these celestial misfits. We now know that retrograde motion is an optical illusion caused by Earth passing the slower planets but to the ancients, it was a mystery and led to the creation of many fanciful, but always wrong ideas.
Back to Jupiter and Uranus.
Tonight, the two gas giants are just two days from the closest pass of their third and final approach. . Closest approach is January 4 when they will be almost exactly a half degree apart. For comparison, hold your little finger at arm’s length as it approximates 1 degree of arc. The good news is that, for all intents and purposes, the planets will be about the same distance all week as, even in a telescope, the variations in distance will be virtually impossible to detect.
Now, how about seeing the planets?
The good news is that this will be easy to do, provided it is clear. The Cleveland weather forecast for the week is looking mixed, with some days being mostly clear and others looking to be cloud-outs To find the planets, go outside just after dark and look high in the Southwest to see brilliant Jupiter, which is the brightest object in the evening sky. To get Uranus, put some binoculars or, even better, a telescope at low power on Jupiter and look for the distinctly green “star” above the planetary king.
Good luck and clear skies to all.
For more astro news:
Do the ISS wave on Twitter
New Zealand releases 60 years of UFO files
Featured sight for week of 12/26: Mercury rising
The Christmas blizzard from space
See Jupiter and Uranus tonight
Jennifer Aniston compared to Crab Nebula
Celebrate the new year with the Dog Star
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