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Can an Astronaut on Mars distinguish the Earth from its Moon?

Some day an astronaut will stand on Mars and look back at Earth. As Alfred, Lord Tennyson wrote

Venus, Hesper,
Were we native to that splendour or in Mars
We would see the globe we groan in,
fairest of their evening stars
Could we dream of wars and carnage,
craft and madness lust and spite
Roaring London, raving Paris,
in that peaceful point of light?
Would we not, when gazing heavenward,
at a star so silver-fair
Yearn, and clasp the hands, and murmur:
Would to God that we were there?

But what exactly will one see from Mars? An observer on Earth needs a powerful telescope to see the tiny moons of Mars, Phobos and Deimos, but our own moon is much larger, and orbits at a greater distance. Could the unaided eye of an observer on Mars tell apart the Earth and its moon, at their greatest separation?

One might ask a similar question about the four big moons of Jupiter, discovered by Galileo. They are about as big as our own moon. Could an observer on Earth distinguish any of them from their planet?

Grade Level: High School (9-12)
Curriculum Topic Benchmarks: S1.4.1, S15.4.5, M1.4.2, M1.4.8, M5.4.10, M5.4.12, M9.4.7
Subject Keywords: Planetary Comparison, Mars, Jupiter, Earth, Moons

Author(s): David Stern and James Foster
PUMAS ID: 06_19_01_01
Date Received: 2001-06-19
Date Revised: 2001-09-25
Date Accepted: 2001-09-26

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Comments

Comment by Loren Meissner on September 4, 2004
"I'm a retired mathematician/computer scientist, now mentoring some students on Science Fair projects at Presentation High School, San Jose CA, where my granddaughter has just enrolled as a Freshman.
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According to this article, the astronaut could easily see two separate objects.
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But it does not mention the question: whether the Astronaut could tell which is Earth and which is the Moon.

I guess the main question would be, could he tell which is larger and by approximately what factor?

???"

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