1. Star Notes
Everything scientist know about a star they determined by looking at a dot. .

2. Star Chart Coordinates
Right Ascension
Count to the left
24 hours of RA
hours, minutes, seconds
Declination
Count up & down
90 degrees of Dec
+ & -, not N & S

3. Apparent Magnitude
In the magnitude system, m = 0 is a very bright star and m = 6 is at the naked eye limit. As m increases, brightness decreases.
A change m = +5 corresponds to a factor of 100 decrease in brightness

4. Naming a Star First word is the Greek letter of the alphabet
Second word is the name of the constellation
Alpha Centauri
Alpha Scorpii
Delta Tauri

5. What can we know about a star?
Its surface temperature
the Sun is a yellow star (the solar spectrum peaks in the yellow part of the electromagnetic spectrum)
the Sun’s photosphere has a temperature of 5800 K
white and blue stars are hotter than the Sun
orange and red stars are cooler than the Sun
Infrared are warm
Its brightness
intensity = L/4D2
L is (luminosity) proportional to R2T4
(R is radius of star; T is temperature)

6. Stellar Parallax
In astronomy, we measure position in angles. The arc second (1” = 1/3600) is the standard unit for measuring small changes in position.
The parallax, p, is a star’s apparent shift (measured in ”) as a result of the Earth’s orbit around the Sun.
The distance to the star, in parsecs (pc) is Its distance
distance (parsec) = 1/parallax (in arcsec) d = 1/p
1 pcs = 3.26 light years

9. Temperature and Color
Different spectral type stars have different surface temperatures: their spectra peak at different wavelengths, making them different colors.
The intensity ratio in the blue and visible optical bands is a measure of a star’s “color”

10. The spectral sequence spectral type O B A F G K M
mnemonic Oh Be A Fine Girl Kiss Me
temperature
color       

12. Star: Betelgeuse
Spectral Type: M2 I
Parallax: ″
Distance: 131 pc
Apparent Magnitude: 0.41
Luminosity: 38,000 L☼
Star: Procyon
Spectral Type: F5 IV-V
Parallax: ″
Distance: 3.50 pc
Apparent Magnitude: 0.37
Luminosity: 7.4 L☼
Star: Rigel
Spectral Type: B8 I
Parallax: ″
Distance: 237 pc
Apparent Magnitude: 0.14
Luminosity: 70,000 L☼
Star: Sirius
Spectral Type: A1 V
Parallax: ″
Distance: 2.64 pc
Apparent Magnitude: -1.46
Luminosity: 26 L☼

13. Absolute Magnitude The intensity depends on luminosity and distance.
I = L / 4d2
The apparent magnitude a star would have if it were at a distance of 10 pc is called the absolute magnitude, M.
The difference between the apparent magnitude m and absolute magnitude M is called the distance modulus: m - M = 5 log d - 5
This way, when we know the apparent magnitude m and the parallax p, we can calculate a star’s absolute magnitude, M.

14. Relative Luminosity Luminosity of Star = R2 x T4
How much brighter is a star that is twice as hot and three times bigger?

15. Relative Luminosity Luminosity of Star = R2 x T4
How much brighter is a star that is twice as hot and three times bigger?
(3 x 3) X (2 x 2 x 2 x 2)
9 X
144 times as much light given off

17. Star Chart