Astrophysics Flashcards
What is apparent magnitude?
m - brightness measured by an observer at a specific distance
What is absolute magnitude?
M - it is defined as what its apparent magnitude would be if it were 10 parsecs away from earth
it is based on the power output of an object, it does not depend on distance.
What are the units for luminosity
watts
what is the formula for luminosity
L = 4pie x d^2 x b where d is distance from, and b is intensity
how do we draw convex lens’s
arrow pointing outwards
how do we draw concave lens’s
arrows pointing inwards
what is the principle focus
where the light rays meet and cross
what is the principle axis
horizontal to the lens
what is the focus length
distance from lens to focal point (f)
what is magnification
(M) a ratio of size to actual size
a shorter wavelength of light has a shorter focal length, which colour has the shortest focal length.
blue has the shortest focal length
if the resolving power is high
the lower minimum angular resolution
two light sources can only be distinguished when?
their airy discs from one source is at least as far as the first minimum of the other
collecting power is proportional to what?
dish diameter squared or area
how do you remember star classification
Oh Boy, An F Grade Kills Me.
what is the colour of an O star
blue
what is the colour of an M star
orange/ red
what are the temperature ranges for an O star
greater than 30,000 k
what are the temperature ranges for an B star
10,000 to 30,000 k
what are the temperature ranges for an A star
7,500 to 10,000 k
what are the temperature ranges for an F star
6,000 to 7,500 k
what are the temperature ranges for an G star
5,200 to 6,000 k
what are the temperature ranges for an K star
3,700 to 5,200 k
what are the temperature ranges for an M star
2,400 to 3,700 k
which class of star has strong hydrogen lines?
A / B
how do you plot a black body radiation curve
use wines law to find the max wavelength then plot a skewed bell curve
what special lines appear in a O star?
ionised helium
what special lines appear in a B star?
helium, some hydrogen
what special lines appear in a A star?
strong hydrogen, some ionised metals
what special lines appear in a F star?
hydrogen, ionised calcium and iron
what special lines appear in a G star?
neutral and ionised metals, especially calcium
what special lines appear in a K star?
neutral metals, sodium
what special lines appear in a M star?
strong titanium oxide, very strong sodium
what must you refer to when comparing size of stars
spectral class and thus temperature
if a star has a greater power output what else must be true?
it must have a larger surface area
how can we work out the temperature of a star knowing its max wavelength of a black body radiation curve
wiens law
explain what is meant by a parsec
distance at which the radius of the earths orbit subtends at an angle of one arc second
if a star has the same brightness/power as another star how to we tell which is larger
the hotter star will be larger due to stefan’s law
why do classes A and B have the most prominent hydrogen balmer lines/
their temperatures are between 10 and 30 000k which is hot enough to have hydrogen in n=2 state
describe the radial velocity method
the star causes a periodic doppler shift of light received due to the star orbiting a common centre of mass. red shift could then increase and decrease periodically showing there is an exoplanet orbiting
how do we use Hubbles constant to find the age of the universe?
divide by 3.08x10^19 for k ms-1 Mpc-1 then 1/ans
