Stargazing sessions with Stellarium

Posted by Greten on 12 Dec 2020 under Tools

One of the most exciting activities in science classes is conducting stargazing sessions using a telescope. The school might have its own telescope, the science teacher may arrange for an educational field trip to an observatory, or the students may bring if they own one and it's convenient to carry. However, to have a worthwhile stargazing session, you need to prepare for it by determining the exact date, time and place, and what would be the position of celestial bodies on that date and time as seen from that place.

Digital star maps are applications that can help you before and during your stargazing sessions. Before digital star maps where made, people relied on thick tomes containing lists of the celestial bodies' positions at different times to plan their stargazing session accordingly. A basic digital star map will have the options for you to input the time (date and exact hour and minute) and location (in terms of latitude and longitude). Then, it will show you how the celestial bodies will be positioned in the sky as seen from that particular location.

Stellarium is one of the several free and open-source software (FOSS) digital star maps. There are others, but I haven't taken a look at them yet. Stellarium shows planets, stars, constellations, and nebulae as seen from the specified location at a specific time. Stellarium was developed by Fabien Chereau in 2001 and was released under GNU General Public License and available in GNU/Linux, Mac, and Windows. Since then, various functions and data have been added to its subsequent versions.

Stellarium screenshot showing the position of stars and the constellations

I will discuss a few of the functions that you might use often. These basic functions are easy to use so you can explore them by yourself. I'll write entries on other functions of Stellarium if I find anything that is interesting or useful in teaching astronomy.

Installation

For Ubuntu, Stellarium is available through Ubuntu Software Center. You can search it there and when it appears, click the Install button.

For Windows and Mac, Stellarium is available on its official website. For Windows 10, download the EXE file and follow the instructions that appear. I'm not sure how to install it in Mac but considering that the website provides a zip file for download for Mac users, they probably need to extract it in some manner.

Projections of the sky

If you drag your mouse on the main screen (the part where you see the stars, planets, etc.), you will get different possible projections. The changes between the projections is fluid but for the sake of this discussion, let's compartmentalize the possible projections into three: horizontal projection, sky dome projection, and view from above projection. You need to have the ground enable in view to see these projections. Otherwise, all you will see are stars and planets on a black background. Press G on your keyboard to enable or disable the ground.

Horizontal projection

This display is probably the most realistic as you can see the "horizon", the point where the sky meets the ground. However, it's still distorted; in the illustration below, the directions west (W), north (N), and east (E) are visible within a small viewing window. The horizontal projection is the default view when you open Stellarium and is ideal if you are bringing a laptop on the location of your stargazing or you will stargaze where the computer can be easily accessible such as the roof deck of your house.

Stellarium screenshot with an almost plane level ground

You can view the celestial bodies that are not within your view by clicking the center right of the viewing window and dragging horizontally to the left, or clicking the center left and dragging horizontally to the right. You can think of it as the equivalent of turning around in real life.

However, people usually cannot drag the mouse pointer perfectly horizontal and whenever you slide up or down slightly, the ground curves outward or inward. To turn the view while keeping the ground horizontal, use the left and right directional keys of your keyboard.

If you drag the mouse pointer vertically or use the up and down directional keys:

  • Dragging downward or pressing the up key causes the ground curves inward; continuing doing this will turn the ground into a circle enclosing the sky, the sky dome projection.
  • Dragging upward or pressing the down key causes the ground curves outward; continuing doing this will turn the ground into a small sphere with the sky enclosing it: the view from above projection.

To return to horizontal projection, push either up or down keys whichever direction leads to a reduction of the ground's curvature. If you cannot obtain a perfect horizontal, try a small light push to either up or down keys or nudge the center of the horizon with the mouse.

Sky dome projection

In this projection, the whole sky is compressed within a circular area with the ground surrounding the sky. Here, you can see all celestial bodies that are visible in the sky in a given location and given time. The edge of the circular area is the horizon while its center is the zenith, the point on the sky that is directly above you. You will know that a celestial body is already above the horizon if it's already within the circular area.

Whole sky projected as circular area by Stellarium

The four cardinal directions north (N), west (W), south (S), and east (E) orients in a way different from that of the traditional maps. In a traditional map, if the north is up, then east is on the right and the west is on the left. However, in the sky dome projection of Stellarium, if the north is up, then east is on the left and the west is on the right. The reason is that in traditional maps, you are looking at a geographical area from above, while in star maps, you are looking at the stars from below.

To see this view, click on the sky or the ground. Then, press and hold the up directional key until the sky is reduced into a smaller circle. The north direction might not be on top of the circular sky. To rotate it, use the left or right directional keys.

View from above projection

Here, the ground is compressed into something like a small ball or planet with only those celestial bodies near the horizon being visible. You can also think of it as having the sky as a dome, except that you are floating on top of that dome looking below. I could not think of any practical use of this projection.

To see this view, click on the sky or the ground. Then, press and hold the down directional key until the sky is reduced into a smaller circle.

Stellarium projection in which the whole ground is compressed in a small circular area

I just made-up the names of these projections and you need not to memorize them, you only need to understand the description I provided.

Some useful shortcut keys

Below are some of the useful shortcuts when using Stellarium. Most of them have corresponding icons in the user interface.

Display options

The display options control what you can see on the star map.  Most of its corresponding icon lies horizontally at the bottom under the bar that displays location, date and time.

Horizontal icons of Stellarium: twenty-three different icons and their corresponding shortcut keys; not all of them has shortcut keyys shown in this illustration

  • C - show/hide constellation lines, the imaginary lines that connect the stars to form constellations
  • V- show/hide constellation labels, the name of the constellation adjacent to the group of stars that make it up
  • R - show/hide constellation art, graphical representation of objects or creatures that people sees on the constellations from which their names were derived
  • E - show/hide equatorial grid, projection of the globe's latitude and longitude on the sky
  • Z -show/hide azimuthal grid, a grid of latitude and longitude lines similar to equatorial grid except that it is oriented in a manner that instead of converging at the north pole, the longitude lines (called azimuth lines) converge at the zenith.
  • G - shows/hide the ground; if hidden, you will see the celestial bodies below the horizon.
  • Q - show hide cardinal directions; north (N), northwest (NW), west (W), southwest (SW) south (S), southeast (SE), east (E), and northeast (NE).
  • A - show hide atmosphere; shows the color of the sky at a given time and makes celestial bodies invisible if they are really invisible due to the atmosphere, for example, most stars during the day.
  • D - show hide deep-sky objects; mostly nebulae, star clusters, and separate galaxies
  • Alt+P - show hide names of planets; planets are always visible, but their names adjacent to them can be hidden.
  • Ctrl+Alt+E - show/hide exoplanets, the planets outside of the solar system
  • Ctrl+Shift+M - show/hide the source points of meteor showers
  • Ctrl+Z - show/hide satellite hints

Open window functions

Vertical icons of stellarium: seven different icons and their corresponding F1 to F6 and F10 keysThese shortcuts open a window within Stellarium that lets you work on some of its functions. Their corresponding icons are mostly in the vertical panel at the lower left of the Stellarium window.

  • F6 - Location; set the latitude and longitude or search for your city from the list.
  • F5 - Date and time; edit the date and/or time or their combined equivalent in Julian date.
  • F4 - Sky and view options window: several things you can do here such as:
    • set a class of celestial bodies visible or invisible
    • setting the ground (ocean, trees, grass field / Guereins, etc)
    • enable or disable the atmosphere
  • F3 or CTRL + F - search celestial body
    • The starmap will reposition itself and put a marker on the celestial body being searched.
    • If the starmap repositions itself but you cannot find the marker, make the ground invisible by pressing G or clicking the "Ground" button at the bottom panel. You should be able to find the celestial body with the marker. It's not yet on the sky. Press G or click the Ground button again to make the ground reappear.
  • F2 - Configuration: modify language settings, show/hide additional buttons, and other things that affect how Stellarium works.
  • F10 - Astronomical calculations window: displays numerical data about the celestial bodies, predicts transits, and other forecasting functions
  • F1 - Help: opens the help window that list all commands and functions
  • Ctrl+Alt+M - Meteor Show Search: enter a range of dates and search for meteor showers happening between those dates

Other miscellaneous commands

  • Screenshots
    • CTRL+S - save the screenshot as stellarium-nnn.png in the Screenshot Directory, where n is an integer from 0 to 9. By default, the Screenshot Directory is the Home folder in Ubuntu and the Pictures folder in Windows 10 but you can modify this by pressing F2 to open the Configuration window and going to Tools tab.
    • Print Screen (PrtSc) - save the screenshot as an image file in Ubuntu, or copy it to clipboard in Windows.
  • CTRL+Q - close or quit Stellarium.

Last updated on 12 Dec 2020.

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