# How big would the Earth look from the Moon?

Imagine standing (somewhere) on the Moon's surface. How big would the Earth look from the Moon, compared to the image of the Moon we see from Earth? What would be the ratio between the diameters of each body? How would this ratio be calculated? Any help with answering such a calculation would be highly appreciated.

• Do you know the respective physical diameters of Earth and Moon?
– pela
Commented May 23, 2017 at 11:35
• For the moon 3.479 × 10^3 Km, and for Earth 12.75632 10^3 Km Commented May 23, 2017 at 11:45
• Since the angular diameter of an object is proportional to the ratio between its size and its distance (and since the distance from Earth to Moon is equal to the distance from Moon to Earth), the ratio you request is the same as the ratio between those numbers.
– pela
Commented May 23, 2017 at 11:59
• Almost 4 times bigger. Commented May 24, 2017 at 1:27
• Besides knowing the ratio of apparent sizes, you should also know about how it is measured without comparison. There is also a unit of measuring the apparent size of planets and other bodies in space. The measurement is called 'Angular diameter' and the unit is 'arc minute' and 'arc second'. You can find the details easily by searching 'angular diameter' over the net. Commented Nov 15, 2018 at 8:51

For the answer to #1 (and #2), it is the ratio between the numbers (of the Earth's diameter of 12,742 km and the Moon's diameter of 3,474 km) which is $$Earth:Moon = 3.668:1$$ as @pela's comment mentions.