THE APPARITIONS OF MARS AND JUPITER ARE UNDER WAY.
Photo credit: Richard Bosman: CLICK photo to view full size and see below for links.
Jupiter and the Red Planet are coming, growing ever larger in our night sky throughout the winter. Ok, it’s Halloween Week; give me a break I had to make it sound scary. Soooo what the heck is going on you ask? And what are “Planetary Apparitions”?! Well, hopefully this post will help with that.
Using Mars and Jupiter as my examples as they are currently undergoing apparition lets delve into some simple orbital mechanics. When Earth is directly between the Sun and Mars or Jupiter, that’s called OPPOSITION. It’s when a superior (outer) planet is on the opposite side of the Earth as the Sun which places them at perigee (As close as they get to Earth in our current orbits). CONJUNCTION is when Earth and a superior (outer) planet are directly opposite the Sun relative to the Sun. In short, it’s when a planet is on the other side of the Sun from us and as far away is it gets from Earth in its current orbit (apogee).
Apparition is when an outer planet leaves conjunction and begins its western elongation on its way to once again reaching opposition. When you see outer planets in the east at night or before sunrise they are in their western elongation phase (I know, just trust me). Here’s the important thing to keep in mind; when a planet first leaves conjunction it’s as small as it can appear in the sky because it’s on the other side of the solar system. As we catch up to those planets (because we have the inner orbit) each night they grow in size until they enter into retrograde motions, opposition and become as large as they can be in the night sky from our vantage point. That’s what apparition is, a planet growing larger in the night sky because it’s transitioning from conjunction to opposition.
The photo you see above is an entire 2007/2008 Mars cycle, from just after conjunction (small), to opposition (BIG) and once again returning to just before conjunction (small). It’s easy to see here how much the planets size appears to change as it goes through its cycle. You can’t actually see a planet at the moments of exact superior conjunction because it’s behind the Sun relative to Earth.
On April 18, 2013 Mars reached conjunction. At that time it was about 3.5” arcseconds in size on our night sky. Its apparition began shortly after and will continue until it reaches opposition on April 8, 2014. At that time it will be as big as it gets in our night sky at an angular diameter of around 15” arcseconds at an apparent magnitude of -1.4.
On June 19, 2013 Jupiter reached conjunction. At that time it was about 29.8” arcseconds in size on our night sky. Its apparition also began just after that and will continue until it reaches opposition on January 5, 2014. At that time it will be as big as it gets in our night sky at an angular diameter of around 46” arcseconds at an apparent magnitude of -2.7.
Size definitely matters in this case because as you can see, apparent to us here on Earth, even though Jupiter is MUCH farther away than Mars it gets twice as large on our night sky. Even at its smallest angular diameter, Jupiter appears larger than Mars at its largest.
I don’t want to get too deep into it but as far as basic planetary mechanics, the inner planets work a little bit differently. Because they have orbits smaller (Inner) in comparison to Earth, when they leave superior conjunction (as it’s called for the inferior planets) they are in apparition during their eastern elongation phase until they hit inferior conjunction (Not opposition because they aren’t opposite us at all). So when you see Mercury or Venus in the west at or after sunset (as they are now) as evening stars they are growing larger in the night sky as they are becoming more and more crescent. Think of it this way, they see US as we see the outer planets.
If you want to see where the planets are NOW check this page I created on how to create a scale model of the solar system. There are a few links at the bottom of the post that display the current position of the planets: https://danspace77.com/build-a-solar-system/
Richard Bosman’s amazing Mars photo collection: http://www.astrofotografie.nl/Mars.htm
Mars 2014 opposition data: http://in-the-sky.org/news.php?id=20140408_14_100
Jupiter 2014 Opposition data: http://in-the-sky.org/news.php?id=20140105_14_100