# Why is the earth so small when observed from the moon?

I recently discovered the pictures from DSCOVR taken at the Lunar Transit in 2016.

The earth appears very massive behind the moon, which is a little unintuitive if you consider how small it is when observed from the moon itself. Is there any good example/explanation for this?

• Consider this: how does a billboard fit entirely within the frame of a car windshield, but appear so much larger than the car when both are viewed from far away? trbimg.com/img-5710bd05/turbine/… Commented Feb 18, 2019 at 20:48
• Some things are small but some things are far away Commented Feb 19, 2019 at 10:02
• Sesame Street has an excellent explanation Commented Nov 20, 2019 at 14:47
• Just out of curiosity, what is the effective focal length of the DISCOVR camera? Commented Nov 20, 2019 at 17:26

There is a nice image of Earth (ø = 12,756 km) and Moon (ø = 3,476 km) at the same scale.

It is a matter of size and distance. The Apollo Lunar Module shown in the first image of the question is very close to the Moon, some hundred kilometers only but very far away from Earth, about 360,000 km.

But the distance of the camera to the Moon is much bigger in the second image.

The Moon is very, very tiny when compared to the Sun. But at a total solar eclipse, the Moon covers the whole Sun when seen from the surface of Earth. At a annular eclipse, the Moon is farther away from Earth and does not cover the whole Sun. Of course the distance from Earth to Moon is much smaller than that from Earth to the Sun.

Even your thumb may cover the Sun when you stretch out your arm.

But Earth may look much smaller, even smaller than a single pixel. Look at the Pale Blue Dot "taken on February 14, 1990, by the Voyager 1 space probe from a record distance of about 6 billion kilometers (3.7 billion miles, 40.5 AU)"

• The example helped a lot, even though to me, this feels a bit unintuitive at first. Thank you so much for this great answer to a slightly unsophisticated question. Commented Feb 19, 2019 at 14:25
• @Pascal Thank you for the feedback. Feel free to ask another question if something feels a bit unintuitive at first.
– Uwe
Commented Feb 19, 2019 at 14:45

Supplemental answer, so I can post a picture:

Here's a picture of the Moon and Earth taken by the lunar orbiting Chinese satellite Longjiang-2.

Note the similarity of the size of the Earth to the Apollo picture. The Chinese satellite is farther from the moon than the Apollo modules were when the picture in the question was taken.

If you think about it, the Earth is at the same distance from the Moon that the Moon from the Earth (of course), so the Earth at the lunar surface should be 4 times bigger in appearence.

• This is still true even if you don't think about it ;-)
– uhoh
Commented Nov 20, 2019 at 2:45