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Lecture 4

NATS 1740 Lecture Notes - Lecture 4: Apparent MagnitudePremium

2 pages96 viewsWinter 2019

Natural Science
Course Code
NATS 1740
Michael De Robertis, Alireza Rafiee

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NATS 1740: 11th January 2019
*Understanding goals
- Stellar luminosities
- Stellar temperature
- Steller masses
I. How do we measure stellar luminosities?
- Have a camera to measure the luminosities, and to know how far is the star
- As the star gets bigger and bigger, the star gets less energy
- The further the star, the more it looks fainter
- Brightness of star is what you can really measure
- Brightness of a star depends on both distance and luminosity
- Some looks really bright and some look faint (not because it’s small, but it’s far away)
- You can’t tell exactly which stars are brighter unless you know the distance
- Luminosity: amount of power a star radiates (energy per second = watts)
- Apparent brightness (what you measure on the ground): amount of starlight that reaches Earth
(energy per second per square).
- The energy is conserves, luminosity passing through each sphere is the same
- Area of sphere: (radius)^2, divide luminosity by area to get brightness
- The relationship between apparent brightness and luminosity depends on distance
+ The luminosity is constant speed
Brightness = Luminosity / 4 π (distance)^2
Luminosity = 4 π (distance)^2 x (brightness)
(-) How far away are these stars?
- Parallax angle depends on the distance
- Apparent position of the nearest star shift about an arcsencond as the Earth orbits the Sun
- Parallax is measure by comparing
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