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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
for Ask a High-Energy Astronomer
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