Astrophysics: Spooky Stuff

Question 1

Luminosity

Answer 1

The total power radiated by a star at all wavelengths

W

Question 2

Intensity

Answer 2

The power per unit area at the observer

W/m^2

Question 3

How do you get luminosity from power

Answer 3

Multiply by surface area

Question 4

Apparent magnitude

Answer 4

m

The brightness of a star as seen from Earth

Question 5

For Pogsons scale, and increase in one on the apparent magnitude scale corresponds to what increase in intensity

Answer 5

2.51

aka the fifth root of 100

Question 6

How many times bigger is a fourth magnitude star than a sixth magnitude star

Answer 6

6-4

(fifthrootof100) ^2
2. 51x2.51=6.31 times brighter

Question 7

How many times brighter is a second magnitude star than a ninth magnitude star

Answer 7

9-2=7

(fifthrootof100)^7

631 times brighter

Question 8

What does Pogsons scale allow

Answer 8

Intensity measured to be converted to a numerical apparent magnitude

Question 9

Faintest stars have an apparent magnitude of…

Brightest stars have an apparent magnitude of…

Answer 9

6
-26

Negative correlation between intensity and apparent magnitude
By a 2.51 ratio
Meaning a log scale is used (formula sheet)

Question 10

How far does light travel in a vacuum in a year

Answer 10

356 days
8760 hours
525600 minutes
31536000 seconds
times by 3 x 10^8

REALLY BIG NUMBER!!!

Question 11

1 light year

Answer 11

9.46x10^15m
The distance travelled by light in a vacuum in the time of one year

Formula book astro section

Question 12

Astronomical unit

Answer 12

Value for the mean radius of the Earth’s orbit around the sun

1.5x10^11m

Formula sheet

Question 13

1’

Answer 13

1 arc minute

1/60 degrees

Question 14

1”

Answer 14

1 arc second
1/60 arc minute
1/3600 degrees

Question 15

How do you express 3.1416 degrees in minutes and seconds

Answer 15

type 3.1416 into calculator

press the two buttons above 8

Question 16

How would you find the value of tan(1”)

Answer 16

1 arc second
1/3600 degrees
calculator
=4.85x10^-6

Question 17

Issue/condition to use a diagram of parallax

Answer 17

Two stars are far enough away that they appear static and in the same place

Question 18

What is a parsec

Answer 18

The distance from Earth to a star with a parallax of 1”

Draw a diagram to represent

Question 19

Two assumptions in working out luminosity

Answer 19

No dust/gas absorbs radiation

Radiation is emitted in all directions equally

Question 20

Intensity power equation

Answer 20

I=L/4pir^2

Where L is power/luminosity

Question 21

Ratio for intensity and radius

Answer 21

I1r1^2=I2r2^2

Question 22

Absolute magnitude

Answer 22

Measure of a stars inherent brightness

Apparent magnitude it would have at a distance of 10 parsecs from an observer

Question 23

For m-M=5logd/10, what is d

Answer 23

distance

in parsecs

Question 24

Apparent magnitude corresponds to

Answer 24

intensity

Question 25

Absolute magnitude corresponds to

Answer 25

power/luminosity

Question 26

A smaller more negative value of apparent magnitude

Answer 26

Brighter the star and the closer you are

Hence why sun is -26

Question 27

Less than 10 parsec distance

Answer 27

m-M=negative, fraction in log, m-M<0

Question 28

m=M

Answer 28

10 parsecs away

Question 29

Smaller more negative value for apparent - absolute magnitude

Answer 29

closer

Question 30

Greater than 10 parsec distance

Answer 30

m-M=positive, integer in log, dimmer, m-M>0

Question 31

The lower m…

Answer 31

The brighter it appears

Question 32

The lower M

Answer 32

The brighter it actually is

Question 33

Big bang theory

Answer 33

Universe started off very hot and very dense

Been expanding ever since