Lecture 14, 15, 16

Question 1

The inverse square law :
The –1– flux or —2— —-3— is the amount of energey that passes each second through a –4– meter of the sphere’s surface area that —5— a star

Answer 1

1)observed
2)apparent brightness
3)square
4)surrounds

Question 2

F(obs) = L/ x
what is x ?

Answer 2

4pid^2

Question 3

Measuring luminositites:
apparent brightness is a measure of how –1– a star looks to us
the luminosity is a measure of the star’s –2– —3— output and does not change with —4– .
—5— is the method used in astronomy to measure the —6— brightness of a star

F(obs) is easy to —7—
whereas luminosity is not as easy to measure as need to know —8— d

Answer 3

1)faint
2)total light
3) light
4)distance
5)Photometry
6)apparent
7)measure
8)distance

Question 4

Most common method used to measure distance to stars. The further the star, the smaller it is

Answer 4

parallax

Question 5

Apparent —1—- is a measure of a star’s apparent brightness as seen from —2—

Answer 5

1)magnitude
2)Earth

Question 6

Absolute magnitude corresponds to the —1— magnitude that a star would be at a distance of 10 —2— from Earth.

Answer 6

1)absolute
2)parsec

Question 7

small m =
big m (M) =

Answer 7

1)apparent magnitude
2)absolute magnitude

Question 8

Red stars are —1— than blue stars and have —2— surface temperatures than —3— stars

Answer 8

1)colder
2)colder
3)blue

Question 9

The colour of a star is measured by comparing —1—- obtained by using —2— filters

Answer 9

1)magnitudes
2)different

Question 10

distance is inversely proportional to —1—-

Answer 10

1)parallax

Question 11

Luminosity in terms of b ( = apparent brightness) (1) and in terms of R (2)

Answer 11

4pid^2b
4piR^2boltzmannconst*T^4

Question 12

The Interstellar Medium (ISM)
* The –1– and —2– between stars is known as —3— medium
* Interstellar gas does not significantly —4— —-5— radiation but it does —6— it
* Interstellar dust does!
* Typical grain sizes ~10-7 m —> grain
of sizes ~λ of the wave, —-7—- and
scatter such —8—

Answer 12

1)

Question 13

Any interstellar cloud is called —-1—
* —–2— nebula: shows emission
line spectrum of a hot gas of
100-10,000 —-3—- masses spread
across many —–4—- years (low —5— ).
Mostly made of neutral —-6—– (HI).
Also known as HII regions

Answer 13

1) nebula
2)Emission
3)solar
4)light
5)density
6)hydrogen

Question 14

Dark nebula: made up —– —— (1)
blocking any –2— light coming form
stars that lie behind it.

• Reflection nebula: —2— around
  stars caused by fine grains of dust in
  a lower —-3—- than in dark
  nebulae. Light from the star is
  —-4—- and —-5— by these dust
  grains —> they
  scatter/absorb blue light more
  efficiently than —-6— , giving them their
  blue colour

Answer 14

1) dust grains
2)visible
2.2) haze
3)scattered
4)reflected
5)red

Question 15

The intensity of light from stars is —–1—- as it passes through the ISM (extinction) and it is also —2—- as the bluer component gets scattered or -3- (reddening)

Answer 15

1)reduced
2)reddened
3)absorbed

Question 16

A dark nebula is only dark at certain —-1—-

Answer 16

wavelength

Question 17

To form a star, the force of 1)—— must overwhelm the 2—- — pushing the material 3)——-

Question 18

star formation happens in dark nebulae because they are regions of 1)—— ——- —— 2)—- — — 3)—– ———

Answer 18

1)high density atoms
2)dust grains
3)cold temperatures

Question 19

Protostars are formed when their own 1)——– ——- contracts the 2)——- around them. 3) ——- protostars can be formed around one dark nebula

Answer 19

1) gravitation
2)material
3)several

Question 20

Stellar interiors:
protostars to main sequence stars
depending on the mass with hich they get inot the main sequence their —- —- will doffer

Answer 20

internal structure

Question 21

Stars with a mass of less than 0.08 solar masses (80 times the
mass of Jupiter) cannot reach the main sequence stars
—> ——- dwarfs

Answer 21

brown

Question 22

if the outer layers of a star expands
choose one:
- the surface temperature decreases
-the surface temperature tempertaure increases
-the surface temperature remains the same
-no statement regarding the surface tempertaure can be made.

Answer 22

-the surface temperature decreases

Question 23

core collapses&raquo_space;
1—— internal pressure&raquo_space;
2—— nuclear 3——&raquo_space;
outer layers 4——&raquo_space;
less efficient transfer of 5———&raquo_space; more 6——- and less 7——- temperature

Answer 23

1more
2)more
3)reactions
4)expand
5)energy
6)luminosity
7)surface

Question 24

core expands&raquo_space;
—— internal pressure&raquo_space;
less —— nuclear ——&raquo_space;
outer layers ——&raquo_space;
more efficient transfer of ———&raquo_space; less ——- and more ——- temperature

Answer 24

1less
2)less
3)reactions
4)expand
5)energy
6)luminosity
7)surface

Question 25

when leaving the main sequence stars become ——-

Answer 25

redder

Question 26

Main sequence lifteime
> hydrogen fusion at 1—–
>Decrease number of
2—— in the core
>Less 3——
pressure
>Core contracts
>Increase density and
4——- in the
core
>Increase internal
5——-
> Expansion of 6——
layers (increase star’s
size
>Increase 7——
>Decrease surface
8——-
>Hydrogen at
the core is
9——
> The star leaves
the Main-
Sequence

Answer 26

1)core
2)particles
3)internal
4)temperature
5)pressure
6)outer
7)luminosity
8)temperature
9)depleted

Question 27

> no core fusion
core 1…… and 2…….
Increase in core 3………
Gravitational energy is 4………. into
5………. energy
Heat from the core expands to 6……… ……….
Hydrogen fusiom from just 7……….. the core
Hydrogen rich region 8………..
Helium generated falls into 9……….. core
Core gains 10………. and 11……..
12………. increases
Increase of 13………. pressure
Outer layers 14……..
Surface temperature falls
………. loss

Question 28

The helium flash is more 1————- in stars with masses between 2——- solar masses

Answer 28

1) explosive
2) 0.4 - 2