Question 1

Is this drawing to scale?

Accepted Answer

No, and it cannot be. The moon is drawn about 24 times too close to the Earth, and the sun about 3,151 times too close and 52 times too small. Shrink the Earth to a 16 mm marble and the moon is a 4.4 mm bead about 48 cm away, while the sun is a 1.7 m ball roughly 188 m down the road. What IS true here is every direction and angle: where the sun and moon lie around the Earth, which half of the Earth is lit, and where you are on it.

Question 2

What am I looking at?

Accepted Answer

The Earth from far above its orbit, looking down from your own hemisphere. Sunlight arrives from the top left, so the half of the Earth facing that way is having its day. The marker is the place you chose, the dotted circle inside the globe is the path that spot rides as the Earth turns, and the moon sits at its true angle from the sun.

Question 3

Why does the moon always look half lit?

Accepted Answer

Because from this vantage you are looking at the moon side-on: the sun lights one half of it, and from above you see the boundary edge-on. The phase people see from Earth is not how much of the moon is lit — it is how much of the lit half faces us, and that is the ANGLE between the moon and the sun in this picture. Line the moon up with the sun and it is a new moon; put it opposite and it is full. The phase disc beside the read-out shows the same instant as it looks from the ground.

Question 4

Why do we always see the same side of the moon?

Accepted Answer

Because the moon turns on its own axis exactly once per orbit — 27.3 days for both — so the same hemisphere faces us permanently. Earth's pull slowed its spin over billions of years until the two matched, which is called tidal locking. A wobble in the orbit lets us see about 59% of the surface over time. It also means "the dark side of the moon" is a misnomer: the far side gets exactly as much sunlight, and at new moon it is the fully lit one.

Question 5

Does it show eclipses?

Accepted Answer

No — deliberately. Earth's real shadow reaches well past the moon's orbit, so drawing it would put the moon inside it at every full moon and imply an eclipse every month. What actually decides an eclipse is how far the moon sits above or below the plane of Earth's orbit, and that is the one thing this flat view cannot show. Lunar eclipses have their own pages.

Question 6

How accurate are the positions?

Accepted Answer

The sun and moon positions come from the same solver the rest of the site uses — good to about a minute of time for sunrise and sunset, and to a fraction of a degree for the moon. It runs entirely in your browser, so nothing is cached or stale. The methodology pages set out where each figure stops being reliable.

Question 7

Can I share the exact view I am looking at?

Accepted Answer

Yes. The location, date, time and span are all in the address bar, so copying the URL shares the exact sky on screen. The link builder further down writes one for you if you would rather fill in a form than edit a URL.

Sun, Moon & Earth Movement Simulator for Rapid City, SD

Showing Rapid City44.081°, -103.231°

Simulator settings

What Rapid City’s latitude does to the picture

Rapid City on the rest of the site