SkyCaramba astronomy blog for the week ending March 12, 2011
Mercury and Jupiter will be in conjunction three times over the next three months. The first occasion happens on March 16. The two planets follow the sun by an hour, which means they’ll be easy to spot after sunset from most places on Earth. Just look to the west for two objects brighter than anything else in that part of the sky. Jupiter will be the object to the left.
If you watch from night to night starting before the 16th, Mercury will start off below Jupiter. If you’re watching from a low latitude in the northern hemisphere or anywhere in the southern hemisphere, Mercury will be below and left of Jupiter. Mercury’s position relative to Jupiter is higher each night until it’s finally above and right of Jupiter for all observers.
Then, the planets get too close to the sun for us to see. Still in the sun’s glare, they meet in conjunction again on April 10. And things get really fun in May. On May 10, Jupiter and Mercury meet in conjunction in the morning sky. Their placement and that of the sun’s make this conjunction especially good for southern hemisphere observers.
But that May event is no mere conjunction. It’s a convention of planets with Mars and Venus joining them! I’ll tell you more about that in the weeks ahead. For now, I hope you’re wondering why the triple conjunction of Jupiter and Mercury is happening.
Jupiter happens to be in consistent movement through the sky in March, April, and May. If you could hold the sky still and see the planets through the daytime lighting, Jupiter appears to be moving from the east side of the sun to the west. Mercury, however, starts off going east very quickly. It passes Jupiter on March 16. Then, on March 23, Mercury’s as far from the sun as it’s going to get. That’s called greatest elongation.
The messenger planet starts heading back toward the sun. Quick on the heels of Jupiter, the two meet up again just west of the sun on April 10. Mercury keeps going, reaches greatest elongation west of the sun on May 7, then starts going eastward again for a final meeting with Jupiter on May 10.
Back to our March conjunction. If you could watch the view from Mercury, Jupiter and Earth would be at opposite ends of the sky. But you would see Earth in conjunction with Saturn on the 17th. From Jupiter, you would see Earth and Mercury in conjunction. If you’d like to see how the skies would look from other planets, I strongly recommend the free program Stellarium.
Conjunctions like the ones happening in March and May provide a useful tool for identifying objects that are hard to identify. I admit having never positively identified Mercury without first spotting something else easy to identify nearby. So I’ll be out around March 16 and May 10 looking for those other objects first.