### 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