## 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