|
How Far Is
It?
By Bob Bond
One of the perennial star party questions
is "How far is it?" where "it" is the thing in the telescope field. This
summary information can be used to get a feel for astronomical units and
distances.
Astronomical distances vary by many orders
of magnitude. The units used to measure the distances are tailored to the
distances being measured, just as we use feet to measure our houses and
miles to measure our cities here on Earth.
An AU, or Astronomical Unit, is the
distance from the Earth to the Sun or about 93 million miles. It is a
convenient unit of measure for things in and around the solar system.
A light year is the distance that light
travels in one year, or 5.87 * 10^12 miles. It is a convenient unit of
measure for nearby stars. Even this unit is small once one begins to talk
about the distances to the galaxies.
To relate these two units to each other,
consider the following quote from Burnham's Celestial Handbook, volume 1
by Robert Burnham Jr. By a fortunate circumstance, the number of inches in
a mile is very nearly equal to the number of AU in one light year, a
perfect arrangement for the purpose of constructing mental scale models.
Let us imagine a scale model of the solar system, with the Earth
represented as a speck one inch away from the Sun. Pluto is then about 3.5
feet away from the Sun. The nearest star on this model will be nearly 4.5
miles away. And all the stars are, on the average, as far from each other
as the nearest ones are from us.
The Solar System
Distances are given from the Sun.
| Body |
Distance |
Distance |
Distance |
Diameter |
| Name |
Million Miles |
Million KM |
AU |
Thousand KM |
| Mercury |
36 |
58 |
0.4 |
4.8 |
| Venus |
67 |
108 |
0.7 |
12 |
| Earth |
93 |
150 |
1 |
13 |
| Mars |
142 |
228 |
1.5 |
6.7 |
| Juno |
184 |
296 |
2 |
0.2 |
| Pallas |
196 |
316 |
2.1 |
0.6 |
| Ceres |
240 |
387 |
2.6 |
1 |
| Jupiter |
484 |
779 |
5.2 |
143 |
| Saturn |
870 |
1,400 |
9.5 |
120 |
| Uranus |
1,802 |
2,900 |
19 |
52 |
| Neptune |
2,796 |
4,500 |
30 |
50 |
| Pluto |
3,666 |
5,900 |
39 |
2 |
The Moon is 407,000 KM from the Earth and
is 3400 KM in diameter.
Nearby Stars
Distances are given in light years
Note on star names: The bright stars are
named by constellation and a Greek letter. The brightest star is usually
Alpha, the second brightest Beta, etc. So Vega is also known as Alpha
Lyra, the brightest star in the constellation Lyra.
| Name |
Mag |
Distance |
| Proxima Cen |
11.1 |
4.2 |
| Alp Cen A |
0 |
4.4 |
| Alp Cen B |
1.3 |
4.4 |
| Barnard's star |
9.6 |
6 |
| Wolf 359 |
13.5 |
7.8 |
| - |
7.5 |
8.2 |
| LDS 838 |
12.6 |
8.6 |
| UV Cet |
12.7 |
8.6 |
| Sirius |
-1.4 |
8.6 |
| - |
8.4 |
8.6 |
Bright Stars
Distances are given in light years
| Name |
Star |
Mag |
Distance |
| Rigel Kentaurus |
Alp Cen A |
0 |
4 |
| Sirius |
Alp CMa |
-1.5 |
9 |
| Procyon |
Alp CMi |
0.4 |
11 |
| Altair |
Alp Aql |
0.8 |
16 |
| Vega |
Alp Lyr |
0 |
25 |
| Arcturus |
Alp Boo |
0 |
37 |
| Capella |
Alp Aur |
0.1 |
41 |
| Aldebaran |
Alp Tau |
0.9 |
67 |
| Antares |
Alp Sco |
1 |
142 |
| Spica |
Alp Vir |
1 |
150 |
| Canopus |
Alp Car |
-0.7 |
183 |
| Rigel |
Bet Ori |
0.1 |
351 |
| Betelgeuse |
Alp Ori |
0.5 |
333 |
| Deneb |
Alp Cyg |
1.3 |
1402 |
Some Messier Objects
| Distances are given in
light years. |
| M# |
Name |
Type |
Distance |
| 45 |
Pleiades |
Open Cluster |
380 |
| 44 |
Beehive Cluster |
Open Cluster |
577 |
| 7 |
The Scorpion's Tail |
Open Cluster |
1,000 |
| 27 |
Dumbbell Nebula |
Planetary Nebula |
1,250 |
| 42 |
Orion Nebula |
Diffuse Nebula |
1,600 |
| 47 |
- |
Open Cluster |
1,600 |
| 20 |
Trifid Nebula |
Diffuse Nebula |
2,200 |
| 67 |
- |
Open Cluster |
2,250 |
| 41 |
- |
Open Cluster |
2,400 |
| 97 |
Owl Nebula |
Planetary Nebula |
2,600 |
| 35 |
- |
Open Cluster |
2,800 |
| 21 |
- |
Open Cluster |
3,000 |
| 76 |
Little Dumbbell Nebula |
Planetary Nebula |
3,400 |
| 36 |
- |
Open Cluster |
4,100 |
| 57 |
Ring Nebula |
Planetary Nebula |
4,100 |
| 17 |
Omega or Swan Nebula |
Diffuse Nebula |
5,000 |
| 1 |
Crab Nebula |
Supernova Remnant |
6,300 |
| 8 |
Lagoon Nebula |
Diffuse Nebula |
6,500 |
| 4 |
- |
Globular Cluster |
6,800 |
| 16 |
Eagle Nebula |
Open Cluster |
7,000 |
| 22 |
- |
Globular Cluster |
10,100 |
| 71 |
- |
Globular Cluster |
11,700 |
| 10 |
- |
Globular Cluster |
13,400 |
| 13 |
Hercules Globular Cluster |
Globular Cluster |
22,200 |
| 5 |
- |
Globular Cluster |
22,800 |
| 30 |
- |
Globular Cluster |
24,800 |
| 92 |
- |
Globular Cluster |
26,100 |
| 80 |
- |
Globular Cluster |
27,400 |
| 3 |
- |
Globular Cluster |
30,600 |
| 15 |
- |
Globular Cluster |
32,600 |
| 54 |
- |
Globular Cluster |
82,800 |
| 110 |
- |
Elliptical Galaxy |
2,900,000 |
| 32 |
- |
Elliptical Galaxy |
2,900,000 |
| 31 |
Andromeda Galaxy |
Spiral Galaxy |
2,900,000 |
| 33 |
Triangulum Galaxy |
Spiral Galaxy |
2,300,000 |
| 83 |
Southern Pinwheel |
Spiral Galaxy |
10,000,000 |
| 81 |
Bode's Galaxy |
Spiral Galaxy |
11,000,000 |
| 82 |
Cigar Galaxy |
Irregular Galaxy |
11,000,000 |
| 64 |
Blackeye Galaxy |
Spiral Galaxy |
12,000,000 |
| 101 |
Pinwheel Galaxy |
Spiral Galaxy |
27,000,000 |
| 51 |
Whirlpool Galaxy |
Spiral Galaxy |
37,000,000 |
| 96 |
- |
Spiral Galaxy |
38,000,000 |
| 105 |
- |
Elliptical Galaxy |
38,000,000 |
| 104 |
Sombrero Galaxy |
Spiral Galaxy |
50,000,000 |
| 100 |
- |
Spiral Galaxy |
60,000,000 |
| 84 |
- |
Lenticular Galaxy |
60,000,000 |
| 85 |
- |
Lenticular Galaxy |
60,000,000 |
| 86 |
- |
Lenticular Galaxy |
60,000,000 |
|