Home > Ephemeris Program, stars > 02/22/2018 – Ephemeris – The blue-white star at Orion’s knee

02/22/2018 – Ephemeris – The blue-white star at Orion’s knee

February 22, 2018

Ephemeris for Thursday, February 22nd. The Sun will rise at 7:32. It’ll be up for 10 hours and 49 minutes, setting at 6:21. The Moon, 1 day before first quarter, will set at 1:46 tomorrow morning.

The bright star at the bottom right corner of the big upright rectangle that is the giant hunter Orion’s body in the south-southeast is Rigel. It is a white star with a bluish tinge. It compares in brightness with Betelgeuse at the opposite end of Orion’s rectangle, though it’s usually a bit brighter. The mismatch in color makes brightness comparisons difficult. Rigel is about 860 light years away, It’s 23 times the mass of the Sun, 120 thousand the times brighter than the Sun, and a diameter almost the size of the orbit of Mercury. It’s age is thought to be about 8 million years. It has a visual companion star that can be seen in amateur telescopes. It’s not that dim, but suffers by being close to the arc light brightness of Rigel.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

Orion's named stars

Orion’s named stars including the belt stars. Created using Stellarium.

Rigel A & B

Rigel with its companion star as photographed through a telescope. No attribution. Source: http://washedoutastronomy.com/content/urban-orion?page=1

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