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Observing the Sky
(Stellarium Exercise #3)
All Astronomy begins with looking at the sky. For thousands of years humans have watched the sky at
night, carefully noting the positions of the stars and planets, and how they change as the hours, days and months
go by. Indeed, until modern times, knowing the sky was a matter of life and death! If a farmer misjudged when
he or she should plant his or her crops, or if a nomadic hunter-gatherer misjudged when he and his family should
start moving South for the Winter, the result was certain death! To make observations of the night sky easier
over the millennia, people developed various names for both stars and groups of stars, which are called
constellations.
In this assignment we’ll use Stellarium to observe the sky tonight. We’ll see what stars and
constellations are visible, and try to understand how they move as the hours pass.
PART A
Start Stellarium. Make sure you are observing from Los Angeles (if you haven’t already set Los
Angeles as your default home location) by opening the Location window (Find the Location icon at the lefthand side of the screen, or simply press the F6 key), entering Los Angeles in the search bar, and then clicking on
Los Angeles, United States. Close the Location window.
Zoom out until the Field of View (indicated by FOV in the Information Bar at the bottom of the screen)
is about 180°. Then drag the horizon around until the sky is centered on the screen and North is at the top.
You should see the sky as a complete circle, centered on your screen, with the horizon (North, South, East and
West) forming the edge of the circle, and the zenith at the center.
Turn the atmosphere off (if it is on) by pressing “A”. You should see a sky full of stars (and perhaps
some planets and asteroids). Set the time for 9 PM (21:00 in “military time”) by clicking on the Date/Time icon
on the left-hand side of the screen (or by simply pressing the F5 key) and adjusting the time.
As you click on various dots in the sky (almost all of which are stars), a cross hair appears over your
selected star, and information about the star appears in the upper left-hand corner of the screen. There’s a lot of
information here, including, on the first line, the various names of the star. The first name listed in that top line
is the common name of the star. Let’s start with those names. Find the three brightest stars in the sky (the three
biggest dots) and click on them one at a time.
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What are your three stars’ common names? 1:______________ 2: _____________ 3: _______________
In each star’s information listing, on the second line from the bottom, the distance to the star is listed, in
light years (a light year is the distance light travels in one year).
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What are the distances to your three stars? 1:_____________ 2: _____________ 3: _______________
You might recognize some of these stars. Each of these stars is part of a specific constellation, or area
of the sky assigned to a particular mythical character, object or animal. To see the stick-figure outlines of the
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constellations, press the “C” key on your keyboard, or click on the Constellation Lines button in the toolbar at
the bottom of the screen. Lines appear connecting the brightest stars in each constellation. To show the names
of the constellations, press the “V” key on your keyboard, or click on the Constellation Labels button in the
toolbar at the bottom of the screen. Many of these constellation names should also be familiar.
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Name the three constellations that contain your three stars: 1:__________ 2: __________ 3: __________
As you can see, it’s hard to tell where in the sky one constellation ends and the next one begins. To see
the official borders between constellations, press the “B” key on your keyboard. The constellations’ boundaries
appear as red dashed lines. These borders are arbitrary, kind of like the borders between states – but astronomers
have agreed to define them precisely, so that every spot in the sky (and hence every star) is in exactly one
constellation. To see pictures of the mythical characters associated with each constellation, press the “R” key on
your keyboard or click on the Constellation Art button in the toolbar at the bottom of the screen.
Change the time to 9 PM on today’s date (open the Date/Time window or press the F5 key), then answer
the following questions (It may be easier to see the constellations if you zoom in or out and drag the sky around
to re-center it):
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What constellation is just above the Southern horizon at 9 PM tonight? ___________________________
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What constellation is just above the Northern horizon at 9 PM tonight ? __________________________
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What constellation is at the Zenith at 9 PM tonight? __________________________________________
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How many constellations are in the sky at 9 PM tonight? (count them!) __________________________
Open the Search Window (type CTRL-F or press F3) to help you find the following objects.
Remember, once you’ve typed the name of an object in the Search window, hit Enter and that object will be
selected and centered on screen. If the object is hidden by the Earth, press the “G” to key to hide the ground.
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Find the constellation Ursa Major. Name two stars it contains. (Remember, click on a star to see its
name.) __________________________________________________________________
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Find the star Rastaban. What constellation is it in? __________________________________________
Find the star Arcturus. Look at the information that appears on screen about it.
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How far away is Arcturus? _____________________________________________________________
Display the labels of the planets and the bright stars by pressing the Planets Labels button in the toolbar
at the bottom of the screen (or by simply pressing the P key). If you don’t see any planets labeled on screen,
open the View window and, in the Sky sub menu, make sure there is a check mark next to the Show Planets box
in the Planets and Satellites section. Close the View window. Zoom back out to see the whole sky. Make
sure the constellations are displayed. If they aren’t, press C, V and B until you see them, their names and their
borders.
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Is the Moon out right now? _____________ If so, what constellation is it in? ____________________
Set the time for 1 PM on today’s date. Again, make sure that you can see the whole sky by
zooming out and dragging the sky around.
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Find the Sun. What Constellation is it in? ______________________________________________
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Now let’s see what the sky looked like on August 10, 2005. Enter this date in the Date/Time window.
Set the time for 9 PM. Find the Moon in the sky and center it.
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What bright, named star is the Moon near? __________________________________
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What constellation is this star in? ______________________________________________
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What constellation is the moon in on August 11? __________________________________
Remember, rather than re-entering the new date information each time, you can simply press the “=” key
to advance the time by one day.
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What constellation is the Moon in on August 12? ________________________________________
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What about August 13? ______________________________________________________
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What about August 14? ______________________________________________________
Note that the Moon jumps around in the sky from night to night!
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What explanation can you come up with for this motion?
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As we saw in the previous assignment, there are many things to see in the sky besides stars, including
planets, comets, asteroids, galaxies, nebulae, star clusters, and much more!… These last three objects are called
Deep Sky Objects. Each of these is a distant object much bigger than a single star and permanently located at a
certain spot in the sky, in a particular constellation. There are many catalogs of Deep Sky Objects, most of
which were published in the 18th or 19th centuries, including the NGC catalog (the New General Catalog), the
M catalog (named after French astronomer Charles Messier), and the IC catalog (the Index Catalog).
Stellarium uses the NGC, IC and the M catalogs. To show the labels in the sky for the brightest and most
famous of these Deep Sky objects, press the Nebula button in the toolbar at the bottom of the screen, or simply
press the N key. The brightest NGC/IC/Messier objects are labeled in the sky.
Use the Search window (remember, you can access it simply by pressing the F3 key) to find and select
the Deep Sky Objects below. You may have to zoom in or out to see them and their locations more clearly. If
the object is below the horizon right now, press “G” to make the ground disappear. Remember, information
about the objects appears in the upper left-hand corner of the screen.
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What constellation is the Dumbbell Nebula in? _________________ What is its M number?________
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What constellation is the Trifid Nebula in? ___________________ What is its NGC number?________
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What constellation is the Ring Nebula in? _____________________ What is its M number?_________
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What constellation is the Pleiades in? _____________________________________________________
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What constellation is the Triangulum Galaxy in? ___________________________________________
PART B
There have been numerous methods devised over the centuries to identify stars. The oldest and most
obvious way is to simply give the stars names. Many of these names have been around for centuries, and many
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came down to us from the Arabs, who were the world’s best astronomers during the Dark Ages, when Western
knowledge was almost wiped out after the fall of Rome.
Reset the Date & Time to the current time by pressing 8, or by using the Date/Time window. Turn the
ground on if it is off (the G key), and turn the atmosphere off (if it is on) by pressing A. Make sure the stars’
names are displayed by opening the View window and putting a check mark next to Stars in the Labels and
Markers section of the Sky sub-menu. Before you close the View window, drag the slider next to Stars to
about halfway to the right. Close the View window. Finally, press C and V to see the constellations and their
names.
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Pick your three favorite common names from all the named stars you see:
a. ________________________________________
b. ________________________________________
c. ________________________________________
The problem with naming the stars is that there are FAR more stars than names, and people around the
world can’t even agree on the names that exist! There have been several other, more scientifically precise
methods devised to identify stars. The Bayer method, created by German astronomer Johann Bayer in 1603,
labels the stars in a given constellation using the Greek alphabet, with roughly the brightest star in that
constellation called α, after the first letter in the Greek alphabet (for example, α Orion or α Ori for short). The
second brightest star is then called β, the third brightest γ, and so on, in the order of the Greek alphabet, which is
α, β, γ, δ, ε, ζ, η, θ, ι, κ, λ, μ, ν, ξ, ο, π, ρ, σ, τ, υ, φ, χ, ψ, ω
In English, these letters are written alpha, beta, gamma, delta, epsilon, zeta, eta, theta, iota, kappa,
lambda, mu, nu, xi, omicron, pi, rho, sigma, tau, upsilon, phi, chi, psi, and omega.
The Bayer method is still in use today, but even it can’t account for all of the millions of stars in the sky!
In the 19th and 20th centuries, various exhaustive catalogs of many hundreds of thousands of stars were made,
including the BSC or Bright Star Catalog, the HD or Henry Draper Catalog, and the HIP or Hipparcos catalog,
which Stellarium uses. These catalogs simply number stars. For example, Sirius, the brightest star in the sky, is
also known as α Canis Major, or HD 48915 or HIP 32349.
In Stellarium, a star’s Bayer name is displayed in parentheses next to its common name. The star’s
Hipparcos (HIP) catalog number is listed after the Bayer name.
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What are the Bayer and HIP designations for each of the stars you wrote down above?
a. Star name: ____________________ Bayer letter: _________ HIP number: ___________
b. Star name: ____________________ Bayer letter: _________ HIP number: ___________
c. Star name: ____________________ Bayer letter: _________ HIP number: ___________
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What are the Bayer & HIP designations for the star Kochab (in the constellation Ursa Minor)? (Use the
Search window to find it)
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Bayer: __________________________ HIP: ___________________
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What is the common name for the star α (alpha) Ursa Major, also known as α UMa ? (Use the Search
window to find Ursa Major, then zoom in and click on the bright stars in Ursa Major until you find it)
_______________________________
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What is the common name for γ (Gamma) Draco or γ Dra ? ___________________________
PART C
Now that we know how to identify the stars and constellations, let’s look at how they move over time.
Zoom out to show the whole sky and center it on the screen, with North at the top of the screen. Press
the Increase Time Speed button three times on the bottom tool bar and watch the stars move. Remember, you
can also do this by pressing the L button on the keyboard three times. Each time you press the button, time goes
10 times faster, so three clicks makes time go 1,000 times faster than normal!
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Which way do the stars move as time passes? (W to E? E to W? N to S? S to N?) _________________
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Find the only star that’s not moving. Click on it. What is its name? ____________________________
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Why do the stars move the way they do? _______________________________________________
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Display the constellations and their boundaries as you did before (by pressing C, V, and B). As you
watch time pass 1,000 times faster than normal, can you find the one constellation that never sets – in other
words, that is always out in the sky here in L.A., no matter what time it is? We call a star or constellation that
never sets circumpolar.
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What is the only completely circumpolar constellation (at least in L.A.)? ______________________
Press the Set Normal Time Rate button to let time pass normally. You can also do this by pressing the
K button your keyboard.
Change your location to the North Pole by opening the Location window and clicking on the very top
edge of the Earth map. Your latitude should change to 90° North – the North Pole! Don’t worry if you’re not
exactly at the North Pole – just try to get the Latitude to as close as 90° North as possible. Close the Location
window. Now press L three times again to make time pass quickly.
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What do the stars do now? _____________________________________________________________
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Now where in the sky (not where on the screen!) is the star that doesn’t move? ____________________
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Does this make sense? Explain ______________________________________________________
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Press K, and then set the location for Singapore (open the Location window, enter Singapore in the
Search box, and then click on Singapore, Singapore), which is almost exactly on the Equator (Latitude = 0°).
Close the Location window. To see the horizon more easily, click on the Sky and Viewing Options icon to
open the View window, click on Landscape on the top to open the Landscape sub-menu, and then click on
Ocean. Close the View window. Finally, press L three times to make time run 1,000 times faster than normal.
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What do the stars do now? _____________________________________________________________
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Now where in the sky is the star that doesn’t move? ________________________________________
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Does this make sense? Explain. ______________________________________________________
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Press K to make time run normally. Reset the location to Los Angeles, and set the time for 12 Noon on
today’s date. Press L three times again and watch the Sun move.
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Does the Sun move along with the stars? ________________________________________________
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How about the Moon (if it’s visible)? Does it move along with the stars? _______________________
You now know how stars are named, how they are arranged, and how they move as the hours pass.
You’re well on your way to becoming an astronomer!
Write a brief conclusion summarizing your results and what you learned in this assignment.
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