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How much color should I be able to see in sky objects through a 10-inch telescope?

Dennis Holt, Concordia, Kansas
blue_snowball
The Blue Snowball (NGC 7662) is one planetary nebula in which you should be able to see color through a 10-inch telescope. // Dave Lassiter
Unfortunately, when you look at distant galaxies and nebulae, you won’t see much color through your telescope. That’s because you’re viewing objects that are too faint to trigger your eyes’ color receptors. (This is the same reason why on Earth we see lots of color in the daytime but not much at night.)
 
However, two classes of celestial objects — double stars and planetary nebulae — break this rule. The reason is their sizes. Stars are point sources, and planetaries typically measure less than 1 arcminute across. (As a comparison, the Full Moon spans 31 arcminutes.) So although they’re not really all that bright, their light concentrates over a small area. In astronomical terms, their surface brightnesses are high. The table above (“Color test”) provides 10 colorful objects to observe.


COLOR TEST
Here are five colorful double stars and five planetary nebulae in which you should see color; they are organized by group and then right ascension. You’ll find the positions of all these objects using Astronomy’s interactive star atlas at www.Astronomy.com/stardome
Object     
Designation Colors
Albireo     
Beta (β) Cygni
Blue and gold
Achird
Eta (η) Cassiopeiae
Yellow and red
Al Rischa
Alpha (α) Piscium
Yellow and blue
Almach  Gamma (γ) Andromedae
 Yellow and blue
Kaffaljidhma  Gamma Ceti
 White and blue
The Little Gem
 NGC 6818
 Green
The Blue Flash
 NGC 6905
 Blue
The Saturn Nebula
 NGC 7009

 Blue-green

The Blue Snowball
 NGC 7662
 Blue
Cleopatra’s Eye
 NGC 1535
 Blue
Michael E. Bakich
Senior Editor
0

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