Nearest Stars

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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10/01/2017