Reference Guide


A brief summary of some of the key measurements, units and calculations in the qualification.

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USEFUL UNITS

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

ANGLES

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

CELESTIAL CO-ORDINATES

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

CIRCUMPOLAR STARS

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

DISTANCES

. 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

DRAKE EQUATION

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.

EQUATION OF TIME

 

• EOT =

apparent solar time – mean solar time

• Mean solar time =

apparent solar time – EOT

• Apparent solar time =

Mean solar time + EOT

MOST USED GREEK LETTERS

alpha

beta

gamma

delta

epsilon

HUBBLES LAW

v = Hd

v = velocity
H = Hubble Constant
d = distance

INVERSE SQUARE LAW

Multiply by the square

KEPLERS THIRD LAW

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


MAGNIFICATION

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

MAGNITUDE

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

Differences in Magnitude 

Difference in Magnitude

Brightness Ratio

1

2.5

2

6.25

3

16

4

40

5

100

POWER & LUMINOSITY

• Watt (W) = Joule per second

PARALLAX

D = Distance
p = Parallax Angle

D =

 1 
Pi

Pi = D/1

RADIAL VELOCITY

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

SPEED, DISTANCE, TIME

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
• Light year (l.y.) = the distance travelled by light in a vacuum in 1 year (63 240 AU)
• Parsec (pc) = the distance at which a star would have parallax of 1 second of arc (3.26 light years.)


TEMPERATURE

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

POWERS OF 10

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