Cheat Sheet


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Earth diameter =

13,000 km

Moon diameter=

3,500 km

Mean Earth-Moon distance =

380,000 km

Mean Earth-Sun (1 AU) =

150 million km

Sun diameter =

1.4 million km

Temperature of the Sun’s photosphere =

5,800 K

. Degree

  • arc minute = 1/60th of a degree
  • arc second = 1/3600th of a degree
  • 15 degrees =  1 hour
  • 1 degree =    4 minutes

  • Right Ascension (RA) = celestial longitude, measured in hours
  • Declination (dec) = celestial latitude, measured in degrees (°)

The formula for working out if a star is circumpolar or not is
D >= 90° - L

D = Declination
> = = Greater than or equal to
L = Latitude

  • 1 AU = 150,000,000 (1.5 x 108)
  • 1 Light Year = 9,460,000,000,000 km (9.46 x 1012)
  • 1 Parsec = 3.26 light years

N = R* x fp x ne x fl x fi x fc x L

  • N is the number of civilizations in our galaxy with which communication might be possible;
  • R* is the average rate of star formation in our galaxy
  • fp is the fraction of those stars that have planets
  • ne is the average number of planets that can potentially support life per star that has planets
  • fℓ is the fraction of the above that actually go on to develop life at some point
  • fi is the fraction of the above that actually go on to develop intelligent life
  • fc is the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
  • L is the length of time such civilizations release detectable signals into space.

EOT =

apparent solar time – mean solar time

Mean solar time =

apparent solar time – EOT

Apparent solar time =

Mean solar time + EOT

α

Alpha

β

Beta

γ

Gamma

δ

Delta

ε

Epsilon

v = Hd

v = velocity
H = Hubble Constant
d = distance

Multiply by the square

Example: Planet A is twice as near to the Sun as Planet B. It receives four times as much light as Planet B.
2 x 2 = 4.

Planets move in elliptical orbits around the Sun.

The Sun-planet line sweeps out equal areas in equal times.
Planets move faster when they are nearer the Sun (perihelion) and slower when they are further away (aphelion).

T = Period/ Time it takes to orbit the Sun
r = mean radius from Sun in AU
T2 = r3
Approximate value

Light year (l.y.) = the distance travelled by light in a vacuum in 1 year (63 240 AU)

Magnification =

Objective focal length
Eyepiece focal length

Eyepiece focal length =

Objective focal length
Magnification

Objective focal length =

Magnification multiply Eyepiece focal length

Resolution =

Wavelength
Objective diameter

M = Absolute Magnitude
m = Apparent Magnitude
d = distance in parsecs


To work out Absolute Magnitude;
M = m + 5 - 5 log d

To work out Apparent Magnitude;
m = M-5+5 log d

Difference in Magnitude

Brightness Ratio

1

2.5

2

6.25

3

16

4

40

5

100

Watt (W) = Joule per second

D = Distance
Π = Parallax Angle

D =

 1 
Π

Π = D/1

Parsec (pc) = the distance at which a star would have parallax of 1 second of arc (3.26 light years.)

λ = wavelength
v = recession velocity
c = speed of light

Speed =

Distance
Time

Time =

Distance
Speed

Distance =

Speed x Time

Speed of light =  300,000 km/s Use 24hr clock e.g. 4pm = 16.00 hrs

  • Celsius (°C) - 0°C = 273 K
  • Kelvin (K) - 0 K = - 273°C
  • Fahrenheit = (9/5)C + 32

Large or Small number can be abbreviated.

10-2 = 1/(10 x 10) = 0.01
10-1 = 1/10  = 0.1
100 = = 1      
101 = 10 = 10    
102 = 10 x 10 = 100
103 = 10 x 10 x 10 = 1000
106 = 10 x 10 x 10 x 10 x 10 x 10 = 1,000,000
M = Mega = Million
K = Kilo = Thousand