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 f_{p} x n_{e} x f_{l} x f_{i} x f_{c} 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
T^{2} = r^{3} 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 = |
Objective focal length |
Objective focal length = |
Magnification multiply Eyepiece focal length |
Resolution = |
Wavelength |
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 = |
Distance |
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
10^{0} = = 1
10^{1} = 10 = 10
10^{2} = 10 x 10 = 100
10^{3} = 10 x 10 x 10 = 1000
10^{6} = 10 x 10 x 10 x 10 x 10 x 10 = 1,000,000
M = Mega = Million
K = Kilo = Thousand