Copyright © Michael Richmond.
This work is licensed under a Creative Commons License.
Today's lab exercise should be carried out in pairs, ideally, but it's okay to do it by yourself or in a group of three.
In order to gain credit for this exercise, you must create a PDF document which provides the answers to all the questions. Submit the PDF to the instructor via the "Assignments" tab in myCourses.
The goal of today's exercise is for you to become familiar with the "Stellarium" program, which allows you to view the sky at any date and time (and from any location). A planetarium is very, very useful for creating a plan for observing some particular object.
Start "Stellarium" on your computer. When it starts, it should show the sky for today's date, at the current time, as seen from Rochester. If it does not, please call your instructor over.
Click on the Sun; a bunch of information about the selected object should appear in the upper-left portion of the screen.
Now use the clock icon (in the pull-out menu at lower left) to change the time. Set the time to 4 PM = 16:00.
Simply changing the time can be very useful.
Okay, let's move on to the sky at night. You should notice that the display changes from bright to dark after the Sun sets. Change the time to 8 PM = 20:00.
Many of the Stellarium buttons in the pull-out menus on the lower-left side and lower-left bottom of the screen are toggles: clicking on the button once activates some action, and clicking on it again de-activates the action.
Play with the constellation lines and constellation labels buttons until you figure out what they do.
You can use the "Page Up" and "Page Down" keys on the keyboard to zoom into and out of the view of the sky. Try zooming at as far as you can; you probably won't see the entire night sky. But if you left-click-and-hold on the "S" at the southern horizon then drag down, you should be able to see the entire night sky as a circle. When you can see the entire night sky as a small circle, call the instructor over to show him.
Make sure you can see the entire circle of the night sky, and then play with the "equatorial grid" and "azimuthal grid" buttons on the pull-out menu at bottom left.
What happens to the positions of stars during the night? They ought to rise in the east and set in the west, right? Well, let's see. Make sure you can see the entire circle of the night sky and then modify the time from 8 PM = 20:00 to 4 AM = 04:00 the next morning.
If you are interested in a particular object, left-click on it to select it, then press the spacebar to center it on the display. You can then zoom in and out to suit your needs. Let's try this with Jupiter.
Set the date to today, and the time to 8 PM = 20:00. Toggle the equatorial grid on, and the azimuthal grid off. Then select Jupiter and zoom in until you can see its large, bright moons. There are four of them: Io, Europa, Ganymede, and Callisto.
One of the tasks for which Stellarium is most useful is planning for future observing runs. It can help you to figure out when your object is visible in the sky, and, even more important, when it is "well-placed" for measurements. As we will discuss later, the Earth's atmosphere absorbs and scatters light rays, especially when the object is only a small distance above the horizon. As a general rule, it's best to observe objects only when they are at least 30 degrees above the horizon.
The very best time to observe a star, of course, is when it is highest in the sky. We call that moment "culmination," or "crossing the meridian."
Pretend that your target is the variable star V347 Aur. What is the observing window for this star? That is, when should you start and end your measurements? Of course, it's not possible to see stars at all, even with a telescope, during the day. Sometimes, your observing window is set by the times of dusk or dawn ...
Copyright © Michael Richmond.
This work is licensed under a Creative Commons License.