Jupiter in the south
Published on Aug 26, 2008 at 5:38 pm.
1 Comment.
Filed under skywatching.
Yesterday was the first day of the semester. It was clear last night, so I took my students out for a look at the sky. On the first clear night, I like to get them to learning stars and constellations. After all, that is one of the things that they all say that they’d like to learn in an astronomy class. Naturally, I give them much more, but I think that it would be nice for them to leave the class knowing how to identify some stars and constellations.
So, the first thing that I teach them is how to use a planisphere. The one that we use with our students is the one by David Chandler, shown here. For those of you new to astronomy, a planisphere is a very simple device that can be set to show what the sky looks like at different times on different days of the year. The sky looks different at different latitudes, so planispheres are made for different latitude ranges. The stars and constellations are labeled, and so once you know how to use the planisphere, you can use it to identify stars and constellations. There’s computer software that does the same thing, but this is much easier to carry around with you.
The first thing to do to try to use the planisphere is to figure out what direction you are facing. So, for those of us in the northern hemisphere, that often means finding the north star. A very widespread misconception is that the north star is the brightest star in the sky. I am not sure why this is such a common belief. I never heard that when I was growing up, but the majority of my students have heard that. Unfortunately, it is wrong. In fact, Polaris, the north star, is not even one of the ten brightest stars. It looks like just another star. The only thing special about it is that it is very nearly over the Earth’s north pole, so it appears to practically stay put in the sky.
But, as I said, there is a common mistaken belief that the north star is the brightest in the sky. So, when we went out and the students started looking for the north star, a large number of the class turned and faced towards the brightest thing that they saw up there. Unfortunately, that object was not Polaris, it was the planet Jupiter, and Jupiter was almost due south at the time. I’ve included a sky view below created by Stellarium software. This shows Jupiter and its position in the sky. Right below Jupiter is a group of stars that makes a pattern that generally resembles a teapot. This is part of the constellation Sagittarius. Off to the west of Jupiter is a reddish star named Antares.
Jupiter is actually quite bright. It was in opposition July 9. At that time, it was the closest that it will be to Earth until next August. It was also brightest then. But, it is still pretty bright. At magnitude -2.5, it is about 60 times brighter than Polaris. Also, at the time that we were out there, it was at almost the same altitude in the sky that Polaris would be. Both Polaris and Jupiter were a little over 30 degrees above the horizon. Jupiter is about as far south as it gets in the sky. Normally, it is farther north, so it would appear higher in the sky when in the southern sky. But, it has not been this far south in about 12 years. It will be about this far south again in another 12 years. Being low in the sky is not good for observing. That means that you look through more air to see it, so there is more distortion. Of course, all that I’ve been saying about Jupiter being low in the sky is for us here in the northern hemisphere. For my readers down in the southern hemisphere, Jupiter should be passing high in the sky in the evenings.
So, my students learned a bit this first night of sky familiarization. There’s still a lot more to learn.
-Astroprof
susy gibler on October 23, 2010 at 11:05 pm: 1
Hi! My sister got a telescope and i’ve been observing Jupites the last three nights, and theres a “thing” that i cant focus below jupiter a little to the right (left, but my telescope inverts the image, i see that thing to the right)… What is that thing? Its about the size of jupites but its like a undefine blur dot… Whats that?? Thanks!!!!