The wait is over as the two brightest planets in the sky, Venus and Jupiter, will waltz their way towards one another in the western sky this week. For months the two planetary luminaries have been edging closer and closer together with Venus being the lower and brighter of the two.
That changes this week as Jupiter will finally be even with Venus on the nights of the 12th and 13th. Jupiter then becomes the lower of the two planets after all these months. Why this is happening gives us insight into the mechanics of our solar system.
All of the objects in the solar system - asteroids, dwarf planets and the 8 main planets - orbit the Sun once in each of their years. An object’s year is defined as how long it takes it to orbit the Sun. For Earth, it takes us 365.25 days to orbit the Sun once. The planets closer to the Sun orbit faster while those farther from the Sun orbit slower.
When we see Venus and Jupiter move in the sky from night to night we are seeing the result of Earth’s motion around the Sun as well as the orbital motion of Venus and Jupiter - all three planets are moving relative to one another. You really get a sense of this motion when these bright planets move each night and this week really highlights it with a closest approach of three degrees or three finger-widths distance.
We see the same orbital motion for our planet every night but in a much smaller sense by the annual migration of the seasonal constellations. Right now the constellations of winter are edging closer to the western side of the sky while the constellations of spring rise in the east. The constellations of summer are well up in the east as the sun rises.
We will be able to see this Venus-Jupiter cosmic dance again and even better in the coming years. May 2013 and especially June 2015 will offer us the chance again to watch solar system orbital mechanics. In June 2015 Venus and Jupiter will be so close they will fit inside the view of a high power telescope eyepiece! That will be stunning to see in the sky with the unaided eye - they will almost merge.
While you are out observing this planetary duo, do an about face and see Mars in the east. It is bright orangish and the brightest object in that section of the sky. I observed Mars with my 10-inch telescope last night and could make out quite a bit of detail. Mars is over 60 million miles away but will be getting closer from here on out with each opposition to follow until it is closest in 2018.
Saturn rises in the east about 10 p.m. and was spectacular in the telescope. Both Mars and Saturn will be coming highlights at our George Mason University Observatory Public Viewing Nights. You can check the schedule at http://physics.gmu.edu/~hgeller/observing.html
Sky Guy in VA (Hoping to get pics this week!!)