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The Question

(Submitted May 29, 1997)

I would like to know if you traveled to the outermost planet in our solar system if the constellations would appear to change their shapes. What about if you traveled to the next nearest star? Or, if you traveled to the center of the Galaxy, ignoring interstellar dust, would you still see the constellations found in the Earth's night sky?

The Answer

What a great question! Thanks for asking and being interested.

The short answer to your question is that you would definitely see the same constellations from Pluto and definitely not from the center of the Milky Way. As far as the nearest star, they would probably be somewhat similar but not completely.

The pattern of stars that we call the constellations we see because of both where we are and where the stars are. Also, all the stars in a particular constellation are not the same distance away.

For example, take the three brightest stars in Orion (Rigel, Betelgeuse and Bellatrix): they are 250, 150 and 210 parsecs away respectively (1 parsec = 1pc = 3.26 Light Years). Now, imagine that you lived on a planet near Betelgeuse, then Rigel and Bellatrix would appear on opposite sides of your night sky; when one is up the other is down. (As an interesting aside, you would not be able to see our Sun from there because it would be too dim).

On the other hand, if you lived on the nearest star (alpha Centauri), which is only 1.3 pc away from us in a different direction, you would not see much difference. This is simply because 1.3 pc is small compared to the 150 pc Bellatrix is away. There are, however, some very close (but much dimmer) stars in Orion (e.g. epsilon Eridani and o2 Eridani) that are only 3.3 and 4.9 pc away. These would appear to move a great deal to someone on alpha Centauri. Also, our Sun would be a bright star in the sky to someone on alpha Centauri, and some other bright stars would appear in a different place (like Sirius, the brightest star, which is only 2.7 pc away).

Thank you again for you thoughtful question.

Jonathan Keohane and Tess Jaffe
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