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Apparent Brightness q (1 Viewer)
- Thread starter lilkatie
- Start date
use the apparent/absolute magnitude formula:
m-M = 5log(d) - 5
m = apparent, M= absolute, d = distance in parsecs.
To use this, though, you need to estimate the absolute magnitude. One way to do this is:
1. Look at the star, get a spectrum of the energy/light emitted from the star (using equipment like a spectrograph...). get information like colour, surface temperature etc.
2. Place the star in one of the spectral classes (OBAFGKMN) according to the data collected in 1.
3. Go to the HR diagram and go to the spectral class (normally x-axis). See what the range of absolute magnitude this section of the main-sequence corresponds to.
4. Plug in formula and you have estimated the distance from the Earth to the star.
I suppose one assumption is that the star in question is a stable star. i.e. it is currently in the 'main-sequence' stage of its life.
As for getting the mass of a planet, I can think of one way right now:
place a satellite in orbit at a specific altitude and measure its period. Use kepler's third law to find the mass of the planet. one problem which may arise is how to work out the radius of the planet.
m-M = 5log(d) - 5
m = apparent, M= absolute, d = distance in parsecs.
To use this, though, you need to estimate the absolute magnitude. One way to do this is:
1. Look at the star, get a spectrum of the energy/light emitted from the star (using equipment like a spectrograph...). get information like colour, surface temperature etc.
2. Place the star in one of the spectral classes (OBAFGKMN) according to the data collected in 1.
3. Go to the HR diagram and go to the spectral class (normally x-axis). See what the range of absolute magnitude this section of the main-sequence corresponds to.
4. Plug in formula and you have estimated the distance from the Earth to the star.
I suppose one assumption is that the star in question is a stable star. i.e. it is currently in the 'main-sequence' stage of its life.
As for getting the mass of a planet, I can think of one way right now:
place a satellite in orbit at a specific altitude and measure its period. Use kepler's third law to find the mass of the planet. one problem which may arise is how to work out the radius of the planet.
Sirius Black
Maths is beautiful
I think there are two assumtions by using apparent brightness to detemine the distance:-
1. the distance of the star from the Earth is always constant coz at such large scale, the slight variation of the distance is negligible for those distant stars
2. The apparent brightness that we used in calculation is the "mean m" by detecting the apparent bightness through certain period then use the period-luminosity relationship to find the corresponding absolute luminosity -Now plug your values into the eqn above
About the mass of the planet, if the planet has a moon, then it is possible to find the mass by applying laws of physics. However, if the planet doesn't have a moon, the most popular method before 2002 was to use "Doppler Method" (or "wobble method")
http://www.space.com/searchforlife/seti_wobble_method_010523.html
But in 2002, someone used "teeter-totter method" (simply find the wiggle of the planet first) found the EXACT mass of a first extrasolar planet and thus Doppler's Method's stark liminations had been revealed. :/
Hope this helps.
1. the distance of the star from the Earth is always constant coz at such large scale, the slight variation of the distance is negligible for those distant stars
2. The apparent brightness that we used in calculation is the "mean m" by detecting the apparent bightness through certain period then use the period-luminosity relationship to find the corresponding absolute luminosity -Now plug your values into the eqn above
About the mass of the planet, if the planet has a moon, then it is possible to find the mass by applying laws of physics. However, if the planet doesn't have a moon, the most popular method before 2002 was to use "Doppler Method" (or "wobble method")
http://www.space.com/searchforlife/seti_wobble_method_010523.html
But in 2002, someone used "teeter-totter method" (simply find the wiggle of the planet first) found the EXACT mass of a first extrasolar planet and thus Doppler's Method's stark liminations had been revealed. :/
Hope this helps.
treelovinhippie
<this space for rent>
I find the distance modulus formula is easier to remember as:
M=m-5log(d/10)
where
M = absolute magnitude
m = apparent magnitude
d = distance (parsecs)
Then in altering that to find d:
d = 10*10^((m-M)/5)
... which is much more accurate than other methods
M=m-5log(d/10)
where
M = absolute magnitude
m = apparent magnitude
d = distance (parsecs)
Then in altering that to find d:
d = 10*10^((m-M)/5)
... which is much more accurate than other methods