This is our second look at the total solar eclipse of July 2, 2019.
This time, we will watch it from the Moon, because that is a good
place from which to get an overall view of how a solar eclipse works.
We will start with a series of short videos showing how to
set up to watch the eclipse. If you watch those, treat them
as a tutorial and follow along in another window. It will
be easier to do that if you have worked throught the Space
Travel Tutorial. We assume that you at least know how to
enter the Planetarium, the first segment of the Stargazing
The last video is standalone. In it, we
just watch the
eclipse, with some commentary. If that is what you
want to do, then just skip to that one.
1. Get onto the Moon.
Open the Control Panel by right clicking the mouse.
Set Space Travel mode.
Set your Home Planet to the Moon.
Leave the Control Panel open.
2. Set up date and time.
Open Date and Time on the Control Panel by left-clicking on that heading.
Press Stop Clock, so the time doesn't
run away from us while we are setting things up.
Set the timezone offset to 0 so we are all using UTC + 0, which is GMT.
Set the date to July 2, 2019 (2019/7/2) and set the time
to 16:30 hours.
Set the Time Rate to 60. That way each hour of Planetarium time
will take only one minute of real time to go by.
3. Set up your view and your location on the Moon.
On the Control Panel, open View by left-clicking on that
Select Earth under Tracking and under View Planet.
Close View by left-clicking on the heading again.
Open Viewer Location.
Set Latitude to about 0.
If you need to, change Longitude until you cannot see the
Close Viewer Location.
4. Set Sun and Earth to correct size.
On the Control Panel, open Planets.
By default, the Earth and Sun are shown 5 times bigger
than they should look, given how far away they are,
how big they are, and how much zoom we are using. The
Planetarium magnifies them so they look a reasonable size in
the sky. The Planetarium never magnifies our home planet,
and that is currently the Moon. There cannot be an eclipse
if, from Earth, the Sun in the sky looks bigger than the
Therefore we must set Sun/Earth Magnification to 1,
meaning no magnification.
Set Brightness Boost down to about 10. Brightness Boost
makes dim stars brighter and bright stars bigger. We are
reducing it just so we won't see any stars that look
ridiculously large compared to the Earth.
Note: Sun/Moon/Earth magnification is explained more fully in
the Control Panel tutorial.
5. Clean up.
On the Control Panel, open Screen Decorations by left-clicking on it.
Turn Lines, Labels, and Direction
Markings OFF. We will leave On-Screen Controls ON.
Close Screen Decorations by left clicking on the heading again.
Close the Control Panel by right clicking.
Exercise: Watch the eclipse for yourself.
Adjust zoom so the earth is a good size.
Adjust your view so about the bottom third of the Earth is
below the middle of the screen. (You can adjust this and
the zoom more during the eclipse.)
Under Date and Time on the Control Panel, press Start Clock.
Close the Control Panel and watch the eclipse.
When it is over, stop the clock again and set the time
back to 17:00 hours. Watch the eclipse again without
starting the clock, by stepping through it minute by minute.
Quiz – after you watch the eclipse:
In which direction does the eclipse move across the Earth? Why?
How does the eclipse start and end?
From the Moon, what does the path of the eclipse look like?
What does the path look like on a flat map of the Earth?
Can you explain the difference?
You might also try watching the eclipse with the Earth as your
home planet, from some distance above it. Then you can adjust
your location to be more or less over the eclipse as it goes on.
6. Watching a Solar Eclipse from the Moon.
This is intended as a standalone video for YouTube, so at the
beginning there will be some repetition of things you already
know. And "link in the description" applies on YouTube, not here.
This is the Dogulean Planetarium, a web page containing an
interactive solar system simulation, written using the
three.js WebGL library. You can find the Planetarium
at dogulean.com, along with videos showing how to
use it. There is a link in the description below.
I have already set up almost everything to watch
the Total Solar Eclipse of July 2, 2019, FROM THE
We want to watch the eclipse from the Moon, because from
there we can watch the whole course of the eclipse and we
will not just learn, but actually see a lot about how
an eclipse works.
It is 16:30 hours, UTC or GMT, on July 2, 2019, with the
clock stopped. We are on the Moon, looking at the Earth, which is
right in front of us.
To see that we are on the Moon, let's LOOK DOWN and then
increase our altitude until we can see the whole thing. The
Sun is behind the Moon and we are in the Moon's shadow, but
the Moon is faintly lit by the glow of the full Earth, which
is behind us.
Let's go back down to the surface now and look back at the
Earth by selecting it on the View Planet menu. Let's get a
good view by zooming in. Let's also position the Earth so
the path of the eclipse across the southern hemisphere, from
about here to about here, is near the middle of the screen.
Lets open the the Control Panel by right-clicking the mouse.
We have set the clock rate to 60 so that, once we start
the clock, one minute of real time will correspond to one
hour of planetarium time. That way the eclipse, which ran
for about 3 1/2 hours from beginning to end in real life,
will only take us about 3 1/2 minutes to watch.
Now let's start the clock and close the Control Panel by
right clicking again.
The Moon always casts a shadow in space. When that shadow
touches the Earth, we call it a solar eclipse. The shadow
moves across the Earth from West to East, because that is
the direction in which the Moon moves around the Earth.
Meanwhile, the Earth also turns from West to East, much
faster than the Moon moves, but not as fast as the Moon's
We see a black spot appearing at the edge of the earth.
In that area, the core of the Moon's shadow is starting to
touch the Earth and the Sun is coming up totally eclipsed.
That is how a total solar eclipse usually starts, and it
usually ends with the Sun going down somewhere, totally
eclipsed, as the shadow slips off the earth.
From our point of view, the area of totality will move
across the Earth in a straight line. If you hold a sheet of
paper over the video at the proper angle, the
eclipse will move along one edge. But if you look at maps
of eclipse paths, they are always curved. That happens
because the Earth is curved and tilted. This part in the
middle of our straight line is farther north than the two
ends. If we drew the path on a flat map of the earth, our
straight line would make a shallow, upside-down U.
From our point of view, the eclipse moves along its path
at a more-or-less constant rate. But from the Earth, at the
two ends of its path, the eclipse travels faster along the
ground, basically because there the ground is at more of a
slant to our straight line. Therefore, at the ends, it
takes less time from start to end of totality, as is appears
from a spot on the ground, than it does in the middle.
At only 3 1/2 hours, our eclipse will be rather brief.
It takes place in the Southern Hemisphere in early
July, at the beginning of winter, and the Eclipse is short
for the same reason that the days are short at that season.
If you look up local times for the start and end of the
eclipse, the difference is much bigger than 3 1/2 hours.
That is because the eclipse moves east, crossing many time
zones, and local time increases by an hour each time it
enters a new time zone.
At this point, we get a good view of the shadow because it
is mostly over clouds. The shadow is dark at the center where the
eclipse is total, greyer outside, where it is only partial,
fading farther away, where less of the Sun is eclipsed.
Totality will continue until the dark part of the shadow falls
off the east edge of the Earth's disk. And now, the Sun has set,
totally eclipsed, somewhere over Argentina.
And that's the end of the total solar eclipse of July 2, 2019.