Astrophysics: Spooky Stuff Flashcards
Luminosity
The total power radiated by a star at all wavelengths
W
Intensity
The power per unit area at the observer
W/m^2
How do you get luminosity from power
Multiply by surface area
Apparent magnitude
m
The brightness of a star as seen from Earth
For Pogsons scale, and increase in one on the apparent magnitude scale corresponds to what increase in intensity
2.51
aka the fifth root of 100
How many times bigger is a fourth magnitude star than a sixth magnitude star
6-4
(fifthrootof100) ^2
2. 51x2.51=6.31 times brighter
How many times brighter is a second magnitude star than a ninth magnitude star
9-2=7
(fifthrootof100)^7
631 times brighter
What does Pogsons scale allow
Intensity measured to be converted to a numerical apparent magnitude
Faintest stars have an apparent magnitude of…
Brightest stars have an apparent magnitude of…
6
-26
Negative correlation between intensity and apparent magnitude
By a 2.51 ratio
Meaning a log scale is used (formula sheet)
How far does light travel in a vacuum in a year
356 days 8760 hours 525600 minutes 31536000 seconds times by 3 x 10^8
REALLY BIG NUMBER!!!
1 light year
9.46x10^15m
The distance travelled by light in a vacuum in the time of one year
Formula book astro section
Astronomical unit
Value for the mean radius of the Earth’s orbit around the sun
1.5x10^11m
Formula sheet
1’
1 arc minute
1/60 degrees
1”
1 arc second
1/60 arc minute
1/3600 degrees
How do you express 3.1416 degrees in minutes and seconds
type 3.1416 into calculator
press the two buttons above 8
How would you find the value of tan(1”)
1 arc second
1/3600 degrees
calculator
=4.85x10^-6
Issue/condition to use a diagram of parallax
Two stars are far enough away that they appear static and in the same place
What is a parsec
The distance from Earth to a star with a parallax of 1”
Draw a diagram to represent
Two assumptions in working out luminosity
No dust/gas absorbs radiation
Radiation is emitted in all directions equally
Intensity power equation
I=L/4pir^2
Where L is power/luminosity
Ratio for intensity and radius
I1r1^2=I2r2^2
Absolute magnitude
Measure of a stars inherent brightness
Apparent magnitude it would have at a distance of 10 parsecs from an observer
For m-M=5logd/10, what is d
distance
in parsecs
Apparent magnitude corresponds to
intensity
Absolute magnitude corresponds to
power/luminosity
A smaller more negative value of apparent magnitude
Brighter the star and the closer you are
Hence why sun is -26
Less than 10 parsec distance
m-M=negative, fraction in log, m-M<0
m=M
10 parsecs away
Smaller more negative value for apparent - absolute magnitude
closer
Greater than 10 parsec distance
m-M=positive, integer in log, dimmer, m-M>0
The lower m…
The brighter it appears
The lower M
The brighter it actually is
Big bang theory
Universe started off very hot and very dense
Been expanding ever since
