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Our Sun, The Nearest Star

Distance from Earth

93 million miles, 8.5 light minutes
Diameter 864,000 miles
Mass 330,000 x Earth
Diameter 109 x Earth
Age 4.5 billon years
Fate Red Giant in 5 billion years
Rotation at equator 25 Earth days
Rotation at poles 35 Earth days
Solar sunspot cycle 11 Years
Temperature at core 27,000,000 degrees F
Temperature at surface 10,000 degrees F
Temperature of sunspots 7,300 degrees F
 

The sun turns 700,000,000 tons of hydrogen into 695,000,000 tons of helium every second by nuclear fusion. The remaining 5 tons is converted into energy. 400,000,000,000,000,000,000,000,000 watts

 

Distances to Other Stars

Distances are particularly easy to calculate if we use the parsec as our distance unit. In that case, the distance of a star in parsecs is:

 D = 1/p

where D is the distance in pc and p is the parallax angle in seconds  of arc. For example, Sirius has a parallax angle of 0.38 seconds of arc  and thus its distance from the Earth is d = 1/0.38 = 2.6 pc = 8.6 LY.   The nearest star (other than the Sun) is the alpha-Centauri system,  which has a parallax of 0.76 seconds of arc, corresponding to a  distance of 1.315 pc = 4.3 LY. Thus, all stars have parallax angles of  less than one second of arc.

 

The Nearest Stars

Name
Dist
(LY)
Spectral
Type
R.A.
Dec.
Luminosity
(Solar Units)
Proxima Centauri
4.2
M5V
14 30
-62 41
6 x 10-6
Alpha Centauri A
4.3
G2V
14 33
-60 50
1.5
Alpha Centauri B
4.3
K0V
14 33
-60 50
0.5
Barnard's Star
6.0
M4V
 17 57
+04 33
4 x 10-4
Wolf 359 (Gliese 406)
7.8
M6V
10 56
+07 03
2 x 10-5
Lalande 21185 (HD 95735)
8.2
M2V
11 04
+36 02
5 x 10-3
Luyten 726-8 A
8.6
M5V
01 38
-17 58
6 x 10-5
Luyten 726-8 B (UV Ceti)
8.6
M6V
01 38
-17 58
4 x 10-5
Sirius A
8.6
A1V
06 45
-16 43
24
Sirius B
8.6
WD
06 45
-16 43
3 x 10-3
Ross 154 (Gliese 729)
9.6
M4V
18 50
-23 49
5 x 10-4
Ross 248 (Gliese 905)
10.3
M6V
23 42
+44 12
1 x 10-4
Epsilon Eridani
10.7
K2V
03 33
-09 27
0.3
Ross 128 (Gliese 447)
10.8
M4V
11 48
+00 49
3 x 10-4
Luyten 789-6 A1
11.1
M5V
22 39
-15 20
1 x 10-4
Luyten 789-6 B
11.1
22 39
-15 20
Luyten 789-6 C
11.1
22 39
-15 20
BD +43 44 A (Gliese 15 A)
11.3
M1V
00 18
+44 61
6 x 10-3
BD +43 44 B (Gliese 15 B)
11.3
M3V
00 18
+44 61
4 x 10-4
Epsilon Indi
11.3
K5V
22 03
-56 47
0.14
61 Cygni A
11.3
K5V
21 07
+38 45
0.008
61 Cygni B
11.3
K7V
21 07
+38 45
0.004
BD +59 1915 A (Gliese 725 A)
11.4
M3V
18 43
+59 37
0.003
BD +59 1915 B (Gliese 725 B)
11.4
M4V
18 43
+59 37
0.002 

How far away is Polaris? Where can I find reliable distances to nearby stars? 

I am trying to find out the distance to the pole star. In one reference I found on the web 300 ly was the figure given while a second source gave 690 ly.  My question for you is what is the distance and is there a > generally accepted reference available on line to get such information?

From: "Ask An Astronomer"

We now have an excellent way to find out the distances to (relatively) nearby stars: the Hipparcos catalog from a European space mission was released last summer. I checked the catalog for you and found that the distance to Polaris is 132 parsecs. There are 3.26 ly in one parsec, so the distance to Polaris is 430 ly. Polaris is a Cephied star, a type of variable star. That makes it tricky to get the distance from the brightness of the star. The Hipparcos satellite made a trigonometric measurement which is more secure. However, the measurement still has an uncertainty of plus or minus 100 ly, which is larger than one would like; the reason is because Polaris is so far away. It is near the limit of what Hipparcos could reach. 

Regards,
Debra Fischer

Introduction to the Night Sky - Part III

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