Ast 111 last test
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how we may find the distance to nearby stars with the method of Stellar Parallax
- The small annual shifts in star's apparent position caused by Earth's motion around the sun.
- Comparing observations of nearby star made 6 months apart
- If we know the stars precise amount of shift
- distant stars have smaller Parallax angle
What are parallax angles measured as?
What is an arcsecond
- 1/60 of an arc minute
- 1/3600 of 1 degree
What is a parsec
distance in parsec = 1/p
P = parallax angle in seconds
distance to an object with a parallax angle of 1 arcsecond; approximately equal to 3.26 light years
The distance light takes to travel in a year
- Measure the brightness of stars on a scale of stellar magnitudes
- Ancient Greeks made sky maps
- #1=very bright, #6 faintest you can see my eye
Today's Stellar Magnitudes
- 5 different magnitudes
- factor in brightness of 100
- EX #1 is 100x brighter than #6
How bright a star appears to be on the sky
Measure the intrinsic brightness of the star
At what distance would a star’s apparent magnitude equal its absolute magnitude?
10 parsecs away
Apparent Magnitude of sun vs. Absolute magnitude
- Apparent = -26.7
- Absolute = +4.5
Astronomers use the various absorption lines in the spectrum of a star to define
Absorption spectra of starts
original classification system based on strength of the hydrogen absorption lines
early spectra types
- A very strong H absorption lines
- P very weak H absorption lines
What do we know governs what spectra looks like more than anything else
Who started the classification system today?
Annie J. Cannon
Spectra types today
- hottest - cool stars
- o0-o9 b0-b9
- The sun is a G2
- A type stars have the strongest H absorption lines
What would you like to do?
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