We suggest that you open another browser window and follow along (and do
the exercises!) in that window.
The description assumes a three-button mouse. If you have some other
pointing device and are in doubt, see
Click on any highlighted text to play the video starting there.
1. The first time you use the Planetarium.
Go to dogulean.com
Press "Enter the Planetarium", the button at top center.
If your browser asks whether to allow the planetarium to
access your location, you should allow it, though you don't
have to. The Planetarium will not send the information off
uses your browser's local storage to store its current
settings, and that is all it stores.
If you accept, then after a few moments, the planetarium
will set your location. Now the planetarium will show you the
sky as it is, where you are, now.
If you don't want to let the Planetarium access your
location, or if you don't have geolocation, or GPS, services, see
"Setting your location manually", below.
2. Setting your location manually.
Click the right mouse button to open the control panel.
Click the left mouse button on "Viewer Location".
Set the latitude and longitude you want using the sliders or
number inputs. You can find your approximate longitude and
latitude by finding the nearest town in a map application or
by Googling it.
You might do this because you can't use
Geolocation or don't want to.
Or you might set a location in the southern hemisphere if
you live in the north, just to see what the sky looks like
If you set a position different from where you are and
want to go back home, then, if you allowed the planetarium
to know your position, you can left-click "Set from
Geolocation". Otherwise you will have to set your real
Close "Viewer Location" by left-clicking on it again.
Close the control panel by right-clicking again or by
The Planetarium remembers settings, including location
from one session to the next.
3. Looking Around.
Now let's learn to look around in the sky – that
means, to change the direction we are looking, which I will
call our direction of view.
All you need to do is hold down the left mouse button and
drag the mouse.
If you drag horizontally, it is like turning around on the
spot. If you drag vertically, it is like looking up or
There is one trick: You are only allowed to look up as far
as the point directly overhead, which is called the Zenith.
If you want to look further that way, turn around by
dragging horizontally and then look down on the other side.
That is part of how the Planetarium makes sure that the
Earth is always level and under your feet.
You may also notice that when you drag in a straight line,
the sky doesn't exactly move in a straight line. That is the
other part of how the Planetarium keeps the earth level. I
will discuss that more in the Space Travel tutorial.
4. Star and Planet Labels.
Now that we know how to look around, let's find out what we
are looking at.
You can turn on star and planet labels by double-clicking
the left mouse button.
CHANGE: There are three label settings now –
All Labels, Planets Only, and None (Labels Off). Double-clicking
cycles through them. We will keep labels on for now.
Constellations are color-coded. Each constellation has a
label and all nearby stars with a label of the same color
belong to that constellation.
This constellation is Pegasus, the winged horse, and all
these stars belong to it.
A star label consists of a designator and possibly a name,
if the star's name is well-known.
There are several kinds of designators, but, for brighter
stars, the designators are usually Greek letters.
It is worth learning at least the first few Greek letters
because usually, though not always, the order of the letters
gives the order of brightness of the stars in the constellation.
So: Alpha α, beta β, gamma γ, delta δ,
Planet labels are all green – a different shade of
green from one we use for star labels. They just give the
name of the planet.
If you don't see any planets right now, don't worry about
it. We will learn how to find them later.
Note: The Greek letters were assigned by Johan Bayer, a German
Astronomer, in 1603, not by the ancient Greeks.
5. Changing Star Label Colors.
If you have trouble distinguishing constellations with our
default star label colors, you can try an alternate color
Right click to open the control panel. Left click on
"Screen Decorations" to open that section.
On the "Label Colors" drop menu, you have a choice of two
color schemes. Choose whichever you prefer. I usually use
the default "Equally Spaced" scheme, but will use Alternate
for these tutorial videos.
Close "Screen Decorations" by left-clicking on it and
close the Control Panel by right-clicking anywhere.
6. Star and Planet Info Bars.
If you put the mouse over a star or a planet, an information
bar will appear. Info bars will appear whether or not
labels are visible.
For a star, the info bar contains:
The star's designator.
The star's constellation, in a form that means "of
that constellation". For example, "Pegasi" means "of
The star's name, if it has one. If the name is less
well known, it will not appear in the label but will
still appear in the info bar.
This one is Markab, Arabic for "the saddle", on
Pegasus, the Winged Horse.
Next, there is the star's position in the sky, given
as Right Ascension (RA) and Declination (D). Those are
sky versions of longitude and latitude. These are
called Equatorial Coordinates and I will explain them
further in the "Lines" segment.
The star's Magnitude. Magnitude is a number
indicating how bright the star is. The smaller the
number, the brighter the star. Magnitude can be zero or
Planet info bars contain the planet's name, the Equatorial
Coordinates showing where it appears to be in the sky, and
its distance from the viewer in Astronomical Units
An astronomical unit is the average distance of the Earth
from the Sun, about 93 million miles or 150 million
A planet's label will appear even if the planet is not
visible, like Uranus here. (What you see here, is not
Uranus, but a star in the constellation Aquarius.) If you
put the mouse pointer near where the planet is, its info bar
The planet will always be near one end or the other of
An info bar may disappear after three seconds – that
is still a work in progress and I have turned it off for
this tutorial. If an info bar disappears and you want it
back, move the mouse off the object and then back on.
7. Zooming in – making the sky bigger.
Now let's learn how to take a closer look at the sky, or
rather, to make things in the sky look bigger. We call
that zooming in. It is like using a variable-power telescope.
There are two ways to do it.
Turn the mouse wheel toward you to make things bigger or away
from you to make things smaller. Once we get back to
the size at which we started, we are at zoom 1. We
can't make things any smaller than that.
If you have a mouse wheel that you can press, like a
third mouse button, hold it down and drag up to make things
bigger or down to make things smaller.
The first way, turning the mouse wheel, will also work with
touchpads and with mice that don't have obvious buttons.
You may have noticed that a lot of stars don't have
labels. As you zoom in, more labels will appear until all
stars have them.
Zoom back out before going on.
Move a planet you can't see, Uranus, Neptune, or possibly
Mercury, to the middle of the screen and zoom in until you
can see it. (Don't forget to zoom back out.)
A star whose greek letter has a number attached to it is a
member of a group. Look around for such stars look at their
info bars. If the infobar lists two stars with the same
Greek letter, you have found a double star with both members
in the Planetarium. Zoom in until the other star's label
appears and you can see both members
distinctly. (The Planetarium currently includes only stars
with maginitude at most 5, so it may not include the dimmer
member of a star pair.)
So far in this tutorial, we have been ignoring the
purple, gold, and grey lines that the Planetarium draws on the sky.
This purple line that goes around the sky at an angle to
all the others is the Ecliptic. It indicates the plane
of the Earth's orbit.
The Sun is always right on the Ecliptic.
The moon and planets are always near it.
The constellations of the zodiac are all along it.
This gold line is the equator of the sky. It is always
directly above the Earth's equator.
This other gold line, at right angles to the equator is
the line of right ascension 180°. Once a day, it is over the
line of longitude 180° on the Earth, and at that moment, every
star is directly above a point on Earth whose longitude and
latitude are the same as the star's right ascension and
The line of right ascension 0°, on the other side
of the Earth, is also gold.
This point, where the purple line and the two gold lines
cross, is called the autumnal equinox. When the Sun reaches
that point, fall will begin in the northern hemisphere.
The curved grey lines that are not quite parallel to the
equator are lines of declination. They are 10°
The other lines, straight and not quite parallel to the
line of Right Ascension 180°, are lines of Right Ascension.
They are 15° apart. That is how far the Earth turns in
The "Lines" button at the bottom left of the screen, turns
the lines off or on. Usually I keep them on to give a sense
of orientation and scale.
9. Viewing a planet.
At the bottom right of the screen is the "View Planet"
button. It is really a menu. If you choose a planet on it,
say Venus, we will look directly at that planet's position,
which means that the planet will appear right in the middle
of the screen.
If we view a planet that is not currently in the sky, say
Mars, we will end up looking at its position, but through
Going back to view Venus again, and bringing up its info
bar, we see that the Venus's coordinates are almost the same
as the ones at the upper right of the screen. In fact,
right after we selected "View Venus", they were exactly the
same. The coordinates at upper right are those of the point
at the center of the screen, but that point keeps changing as
the Earth turns.
10. Date and time.
At the top left of the screen there are controls for
Planetarium date and time.
By default date and time are given for the timezone you
have set on your computer – local time. We have year,
month, day of the month, hour, and minute.
You can change one of the time components by putting the
mouse over it clicking one of the little buttons that will
appear. Or you can press and hold the little button to make
things happen faster.
You can also type numbers in the boxes. That makes
sense mainly for the year, because for other components, the
Planetarium makes a lot of automatic adjustments to keep the
values in the right range.
If you type something wrong, you can type something else,
or get back to something sensible by pressing "Real Time".
That sets the date and time back to Now.
If you want to view a star, planet, or constellation that
can sometimes be seen from your location, but just isn't in
the sky now, changing time is usually the best way to find
For example, let's try to view the moon. Since we are
looking through the Earth toward the east, we know it is not
up yet, so step forward an hour and a bit and we have a good
view of it.
You can also step through time to in order to watch
something in "quick time" that really happens slowly. For
example, if we view the Sun, we can step forward a day at a
time to watch it move along the ecliptic.
That completes this tutorial on Stargazing. Try the
exercises and then explore on your own.