Just how close is that other Earth in Another Earth?

Question

I recently watched Another Earth and I would like to know what the actual distance between the two earths is, using the size of the disks as illustrated in this photo:

Answer 1

To compute the distance you need to know two things, the real diameter of the object in the sky and the degrees of arc its disk subtends in your field of vision. Google says Earth's diameter is 12756.2 kilometers so we'll assume the second Earth has the same diameter.

We'll have to guess at the degrees of arc subtended because we can't know for sure without knowing at least the focal length of the lens used to make the photograph. My assumption is that the whole image covers roughly 34 degrees of arc, as if shot by a 70mm lens on a 35mm camera. The Earth in the sky covers about 11 percent of that image laterally, yielding 3.8 degrees of arc in the visual field.

Divide the diameter of the Earth by the sine of the angle subtended and you get the distance to the second Earth. Using the figures above, the result is around 190000 kilometers, which is way too close for comfort. The tides would be like tsunamis and volcanoes would be erupting worldwide on both planets. People seem not to be running and screaming in the movie trailer, so I assume these effects were ignored in the movie.

Answer 2

Looks closer than the moon. Earth radius is about 3.6 times moon radius, so at same distance, earth should appear 3.6 times as large. In pic, earth looks at least 8 times bigger, so half lunar distance, or so. Incidentally, that'd destabilize the heck out of the moon's orbit. We'd probably end up extinct.

Answer 3

We have another moon in the picture, which we could use as a reference, but we can't tell from the picture whether it is our moon or Another Earth's moon. We especially can't tell because both are full, which means that the sun should have already set and be behind the camera, but it appears to be still light and to the right--look at the bars on the fence on the left of the image.

We know that the ratio of the diameters of the earth to the moon is 3.67, and if you measure carefully you find that in the picture the ratio is about 7.3. So if that's our moon, it's twice as close--190 thousand km. In contrast, if that's their moon, then they are twice as close to us as their moon is to us. Since their moon is ~384000 km from them, that means they're 384000 km from us (and their moon is 768000 km from us).

I slightly favor the latter interpretation since given that the sun is to the right, there's no way that the objects in view are on or near the ecliptic as our moon is. But really, either way, the moon and other Earth should be only partially full, so without that being correct there's no good way to know what is supposed to be depicted.

(Note also that the second earth is almost exactly the same diameter as the person is tall, so we can infer with a high degree of certainty that the other Earth is about 7,500x farther away than the person is.)