Unit 1 - Chapter 5 - Stellar Radiation

Question 1

What is luminosity?

Answer 1

The total power (energy per second) a star radiates. The luminosity depends on the power radiated per square meter (which in turn depends on surface temp) and the surface area of the star.

E.g. Two stars may have the same luminosity, but 1 could have double the surface area and half the power emitted per square meter.

Question 2

What is absolute magnitude?

Answer 2

How bright a star would appear from a distance of 10 parsecs, which allows for a comparison of power emitted between stars.

Question 3

What is the Temperature, Colour and Cause of Absorption lines of an O star?

Answer 3

> 30,000 K
Blue
Ionised Helium

Question 4

What is the Temperature, Colour and Cause of Absorption lines of an B star?

Answer 4

11,000 - 30,000 K
Blue-White
Helium atoms and hydrogen

Question 5

What is the Temperature, Colour and Cause of Absorption lines of an A star?

Answer 5

7,500 - 11,000 K
White
Hydrogen and some ionised calcium

Question 6

What is the Temperature, Colour and Cause of Absorption lines of an F star?

Answer 6

6,000 - 7,500 K
Yellowish White
Ionised Calcium and metal atoms

Question 7

What is the Temperature, Colour and Cause of Absorption lines of an G star?

Answer 7

5,000 - 6,000 K
Yellow
Calcium atoms and metal ions (i.e. Iron)

Question 8

What is the Temperature, Colour and Cause of Absorption lines of an K star?

Answer 8

3,500 - 6000 K
Orange
Metal atoms

Question 9

What is the Temperature, Colour and Cause of Absorption lines of an M star?

Question 10

What type of star is our sun?

Answer 10

A type G star

Question 11

What is apparent magnitude?

Answer 11

How bright a star looks to an observer.
Brightest stars visible with the naked eye = First Magnitude Star
Dimmest Stars visible with the naked eye = Sixth Magnitude Star

Scale defined as the intensity of the brightest star = 100 x the intestine of the dimmest star. This means our sun has a negative magnitude.

Question 12

How can the atmosphere effect the apprentice of stars?

Answer 12

The atmosphere and atmospheric pollution can absorb radiation altering the appearance of the stars, so observatories are placed on high mountains and observations are made from stat elites outside earth’s orbit.

Question 13

How would you calculate a stars luminosity?

Answer 13

Record how intensity varies with wavelength.
Determine at what wavelength maximum intestinal occurs
Use Wein’s law of determine temperature
Work out power emitted per square meter from the surface area (found using the radius)

Question 14

How is a star formed?

Answer 14

1. Gravitational attraction and collapse of a molecule cloud
2. As potential energy is lost, the gas temperature rises
3. Temp and pressure increase drastically, as density gets greater
4. Luminosity is provided by the release of gravitational energy
5. When temp is high enough, nuclear fusion begins creating helium which can also fuse if high enough temp, releasing energy
6. Now a main sequence star

Question 15

What does Hubble’s law state?

Answer 15

That the further away a galaxy is the faster is recessional speed - this is consistent with the Big Bang theory.

v = H d
H = Hubble's constant (65 Kms^-1 Mpc^-1)

Question 16

How can the age of the universe be estimated by Hubbles Constant?

Answer 16

The maximum speed of a star is the speed of light. So the max distance the star could have travel would be d = c / H.
As c = d / t    ;     d = c t
c t = c / H
t = 1 / H.
So the universe's age is given by 1 / H

Question 17

Why does red shift support the Big Bang?

Answer 17

It shows that because the wavelengths of radiation from stars is longer that expected (from labs) then the radiation source must be moving away. Therefore this suggests that stars and galaxies are moving further apart. In terms of visible light, the wavelength are shifted to the red end of the spectrum. This always happens so absorption lines are also shifted.

Question 18

What is the Doppler effect?

Answer 18

Effect observed when there is relative motion between a source and listener. As the waves are being squashed in the way the source is moving and stretched in the other way. So ahead of the source waves have a higher frequency and behind a lower frequency. This can be shown with noise or EM radiation.