One eclipse each month!

Do not touch any of the Factual Changes keys for the time being. Go to the Moon, Look at Earth, and speed up time as much as you need (+ or ++). At some point you will see the Sun pass behind the Earth, and after a while the shadow of the Moon will pass over the Earth. These are the eclipses.

Count the rotations of the Earth between two eclipses. You can count the times your favorite continent reappears. (About 14 rotations, i.e. about half a month.)

Define the Eclipses and apply your knowledge to what you observe. Activate Shadows and change viewpoint.

The good question, at this point, is: why don’t we have one eclipse of the Sun and one eclipse of the Moon each month? The answer is in the fact that the orbit of the Moon around the Earth is not in the same plane as the orbit of the Earth around the Sun. You can see it for yourself by pressing Display: Mark and Factual changes: Moon+. Go to any of the celestial bodies and note when you can see eclipses. When you see one, Pause, then go to other bodies or change the Speed in many ways, and comment on each perspective.

Note: in the default situation (same orbiting plane), if you go to the Moon or to the Sun and look at Earth, you will note that eclipses of the Sun occur at the Equator only.

Note: Scale is such that in Astrini you cannot see total eclipses of the Sun, only partial or annular eclipses.

No more seasons!

Days have the same length at nights only at the Equinoxes. Astrini’s default is a constant equinox! Thus, no seasons, unless you modify the Factual change:Earth parameter. A good vantage point is the Sun (hence Go to:Sun, then Look at:Earth). Before the factual change, you’ll see the same show on Earth each day, day after day. After the change, the show is different each day. One of the poles will be invisible half of the time (half year: count the revolutions of the Moon, each of which corresponds to approximately one month), while the other will be visible.

Some other activities do not require factual changes.

It moves!

Go to the Moon and look at Earth. You will see it spin. The Earth’s rotation was not an agreed upon fact for many centuries, because we do not have a clear feeling that the Earth spins. But if you were an astronomer living on the Moon, you would just see that the Earth spins.

Night and day on the Moon

Go to:Earth and Look at:Moon, and accelerate time a bit (++ a couple of times). You will see the phases of the Moon, i.e. cycles of night and day on the Moon.

Note: Astrini idealizes your position and puts you at the imaginary center of the celestial bodies in the model. Hence changes of tilt in the Earth’s axis and the rotation of the Earth do not entail different views.

Does the Moon Spin?

It does, but as we always see the same face of the Moon, we may be inclined to think it doesn’t. Here too change of viewpoint helps realize what goes on. Go to:Sun, Look at:Moon, and you will see that te Moon does spin. From the Sun’s point of view the fact that the Moon always shows the same face to the Earth can only mean that it has to spin.

Phases in sync

Moon and Earth have the same phase relative to the Sun, but inverted phases relative to each other’s viewpoint. Go to:Earth and Look at:Moon, and wait until New Moon appears. At this point switch viewpoints, Go to:Moon, and Look at:Earth, and you’ll see a Full Earth. If you perfom this switch at other times of the cycle, you’ll see a Waning Moon correspond to a Waxing Earth, and viceversa. And First Quarter on the Moon will correspond to Last Quarter on Earth, and viceversa.

Try out Shadows in this activity.

Observe that if you go to the Sun, it is pointless to activate Shadows. You are the source of light, therefore you cannot see the shadows you cast!