Stars

Question 1

luminosity = ___

Answer 1

power = energy/time

Question 2

brightness = ___

Answer 2

power/area

Question 3

magnitude

Answer 3

number originally 1-6 denoting apparent brightness

Question 4

apparent m

Answer 4

how bright star is from earth

Question 5

absolute M

Answer 5

brightness of star if all of them were 10 pc/32.6 ly away.

Question 6

what can you infer from spectrum of typical star

Answer 6

temperature from dominant color (color related to surface temperature, wavelength of brightest part on spectrum).

composition from dark lines

other; radial motion, magnetic field, etc.

Question 7

spectral type

Answer 7

stars classified according to color/temperature with: O B A F G K M

hottest/bluest (> 25000K) at O, coldest/reddest (<3500 K) at M.

subdivisions exist (G1, G2, …)

Question 8

how to determine star size/radius

Answer 8

direct method: measure angular size in sky and distance = true diameter.

indirect method: absolute luminosity + temperature = size, stefan’s law L - R^2T^4

Question 9

star sizes

Answer 9

supergiants - 100x to 1000x radius of sun, always red.

giants - 10x to 100x radius of sun, can be red or blue or any color.

intermediate - like sun or a little larger.

dwarfs - minimum 8% suns mass
brown dwarfs - too small to fuse hydrogen.

Question 10

parallax method for determining stars distance

Answer 10

as earth orbits sun, nearby star appears to shift position against background of other stars, because the closer it is, the more it moves.

so measuring its two positions over time, if it moves a lot or its parallax angle is bigger, its closer. vice versa.

Question 11

hr diagram

Answer 11

can be understood in terms of stefans law; luminosity for star of radius R and temperature T is L ~ R^2T^4. applicable to red giants and white dwarfs.

relationship between mas and luminosity for main sequence stars; bigger = brighter = shorter lives.