Astro - Star Classification

Question 1

Define apparent magnitude. What is the scale?

Answer 1

A measure of the brightness of the star as measured from Earth. Hipparcos scale, 1-6, brightest to dimmest.

Question 2

What is the equation for I1 / I2 ?

Answer 2

= 2.51^m1-m2

Question 3

What is an astronomical unit in words?

Answer 3

The average distance from the Sun to the Earth.

Question 4

What is a lightyear in words?

Answer 4

The distance travelled by moving at the speed of light for one year.

Question 5

What is a parsec in words?

Answer 5

The distance at which one AU subtends a parallax angle of one arcsecond.

Question 6

What is one arcsecond?

Answer 6

1/3600 degrees.

Question 7

Define absolute magnitude.

Answer 7

The apparent magnitude that an object would have if it were observed from a distance 10 parsecs away.

Question 8

What is the equation for absolute magnitude?

Answer 8

m - M = 5log(d / 10)
m = apparent magnitude
M = absolute magnitude
d = distance in PARSECS

Question 9

Between which numbers for magnitude of a star would be visible.

Answer 9

1-6.

Question 10

On a spectral irradiance over wavelength graph what is the peak value of a curve?

Answer 10

Predominant wavelength, wavelength MAX.

Question 11

What is Wein’s law?

Answer 11

λMAX T = 2.9x10^-3

Question 12

What is Stephan’s law?

Answer 12

P = 𝜎AT^4
P = luminosity

Question 13

What is the intensity law?

Answer 13

I = P / 4πd^2
d = distance from star to observer

Question 14

What are Balmer absorption lines?

Answer 14

A set of visible lines in the spectrum corresponding from n>3 to n=2.

Question 15

What are the spectral classes?

Answer 15

O - oh
B - bollocks
A - am
F - fucking
G - gonna
K - kill
M - myself

Question 16

What are the colours of spectral class in order from O to M?

Answer 16

Blue
Blue
Blue/White
White
Yellow/White
Orange
Red

Question 17

What are the temperatures of spectral class in order from O to M?

Answer 17

25000 - 30000
11000 - 25000
7500 - 11000
6000 - 7500
5000 - 6000
3500 - 5000
< 3500

Question 18

What are the absorption lines of spectral class in order from O to M?

Answer 18

He+, He, H
He, H
H
ionised metals
ionised metals, neutral metals
neutral metals
neutral atoms

Question 19

What are the axis of a H-R diagram? What do you need to remember?

Answer 19

Absolute magnitude over temperature. Temperature goes down from 50000 to 2500. M goes up from +15 to -10.

Question 20

What are the blobs on a H-R diagram and where are they?

Answer 20

White dwarf - round blob, bottom left
Main sequence - long thin diagonal blob, top of y to right of x
- colour classed from hot to cold (O-M)
Blue super giants - round blob between white dwarfs and red super giants
Red super giants - round blob on top right

Question 21

What are the 4 steps in star formation?

Answer 21

1) interstellar dust cloud collapses under gravity
2) GPE decreases, KE increases, temperature increases
3) When temperature reaches 10 million K H nuclei fuse into He
4) Radiation and gas pressure outward forces = gravity inwards forces

Question 22

What will happen in the evolution of a star similar to our Sun?

Answer 22

Main sequence - red giant - white dwarf and planetary nebula

Question 23

What will happen in the evolution of a massive star?

Answer 23

Main sequence - super red giant - supernova - black hole OR neutron star (dependant on mass)

Question 24

What are the features of a neutron star?

Answer 24

Very dense, 4x10^17 kg/m^3
Small, around 10 km

Question 25

What are the features of a black hole?

Answer 25

Extremely dense (like you)
Escape velocity > speed of light

Question 26

How do you derive the equation for the Schwarzschild radius?

Answer 26

0.5 m ve^2 = G M m / rs
rs = 2 G M m / c^2

Question 27

What are type 1a supernovae? What can they be used for?

Answer 27

Happens with stars about the same mass and same brightness curve, they can be sued as standard candles to determine the distance of objects.

Question 28

Where are SUPERMASSIVE BLACK HOLES found?

Answer 28

In the centre of galaxies.