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Stars and Steller Evolution : Lecture 10

Stars

Stars are points of light in the night sky. With the naked eye we can see around 3000. With a telescope we can see many many more. To organise the stars they are gathered together in constelations which often have colourful myths associated with then. During the course I will often look at example of stars from a particular constelation (my favourite..) This is the constelation of Orion . This group of stars is visable in November from about 11pm onwards and is one of the most distinct constelations.

Constelations often have romantic myths associated with them. Purely for fun I include

The myth of Orion

Orion, the hunter of Taurus the bull, and Lepus the hare. Followed faithfully by his companions Canis Major, and Canis Minor, he is the dominator of the northern sky. Madly in love with the daughter of King Oenopion of Chios, Metrope, Orion was consistantly denied marriage to her. His love for her raged, and while in a drunken stupor, raped Metrope. Oenopion consulted Dionysis, and found revenge. Dionysis casted Orion into a deep sleep, and plagued him with blindness. Upon awakening Orion sought the help of an Oracle. It told him that to gain his sight back, he would need to travel east, and let the rays of the sun strike his eyes. Orion did this, regained his sight, and later lived in Crete, where the goddess of the moon Artemis fell in love with him. Her love for him was so strong, that she failed to light the evening sky with moonlight. Orion's death came about when Apollo challenged Artemis to hit a speck among the waters of the ocean, not knowing that this speck was Orion swimming. Artemis shot a single arrow killing him. In response to her actions, Artemis placed Orion, along with his companions Canis Major, and Canis Minor in the sky, near the seven daughters of Oenopion, the Pleiades. Here they remained as the mightiest hunters of the night sky. x

Individual stars also have names - these were mostly given to the stars by Arabic astronomers. (There are a few counterexamples such as "polaris" ) For example the top left star in Orion is Betalgeus and the bottom right is Rigel. In the lecture we named the main stars in Orion. There is also a naming convention which is more comprehensive. This is to give the stars a greek letter - starting with alpha and so forth. Usually alpha is the brightest and so forth. For Orion alpha-Orionis is Betalgeuse and beta-Orionis is Rigel. (For this naming convention we use the possessive form of the Latin name Orion)

Organisation of Stars

We will catagorise stars according to various properties The values of these quantities for the brightest visable stars is given in the brightest stars sheet

Stellar distances

Stars are far from the solar system. We can measure the distance to the stars using parralax This is the same system our eyes use to measure distance. Measuring a stars position in the sky from two different places allows us to measure distance. On earth the best we can do is take measurements 6 months apart at opposite ends of the earths orbit. x Using parralax we can measure the distance to the nearest stars. We use parsecs as a measure of distance. I parsec is defined as the distance at which a star willhave one arc-secondi (1/3600 th of a degree) of parralax. Instead of meters we will use Light Years as a measurement. One light year is the distance light will travel in one year. Since light travels 3x108 m/s
1 Light year = 3 x108 x 60 x 60 x 24 x 364 = 9.4 x 1015 m
1 parsec =3.26 Lyr
The distance from the Sun to the earth is about 500 light secs. Using Parralax the distance to the nearest stars are
  • alpha-Centauri - 4.3 Lyr
  • Proxima Centauri 4.2 Lyr

    Distance to some of the stars in Orion are

  • Betalgues 310 Lyr
  • Rigel 910 Lyr Note that stars in the same constelation are NOT physically close together. Betalgeuse is closer to us than to Rigel.

    © Dave Dunbar 2020