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C O U R S E 
In the Night Sky: Orion
Andrew Norton, The Open University
C O U R S E   L E C T U R E 
Seven Stars and a Nebula
Notes taken on January 6, 2016 by Edward Tanguay
in south east part of sky
three stars in a line
his belt
two stars below are his feet
two stars above are his shoulders
Orion nebula
a diffuse nebula situated in the Milky Way
visible to the naked eye
the closest region of massive star formation to Earth
24 light years across
regions of red and of blue-violet
Greek mythology
Orion was a hunter
he first appears as a great hunter in Homer's epic the Odyssey, where Odysseus sees his shade in the underworld
Artemis was tricked by her brother Apollo and killed her friend Orion
she asked Zeus to put him up in the stars
Orion's stars
red supergiant
second-brightest in the constellation of Orion
ninth-brightest star in the sky
third brightest star in the constellation Orion
27th brightest star
a massive star with about 8.4 times the Sun's mass.
20 million years
old enough for a star of this mass to consume the hydrogen at its core and begin to evolve away from the main sequence into a giant star
stars live different lengths of time, depending on how big they are
a star like our sun lives for about 10 billion years, while a star which weighs 20 times as much lives only 10 million years
multiple star
primary star is a hot blue supergiant
reported to be a double star by amateur German astronomer George K. Kunowsky in 1819
a large blue supergiant star some 1,340 light years distant
275,000 to 537,000 times as luminous as the Sun, and around 34 times as massive
the middle star
1,200 light years distant
one of the brightest stars in the sky
star at the south-eastern corner
a bright supergiant star that has exhausted the supply of hydrogen at its core
the brightest star in the constellation Orion
the seventh brightest star in the night sky
actually a triple star system
Rigel A: a blue-white supergiant
it has exhausted its core hydrogen and swollen out to 79 times the Sun's radius
Rigel B: a spectroscopic binary system, consisting of two main sequence blue-white stars of spectral type B9V that are themselves estimated to be 2.5 and 1.9 times as massive as the Sun