Watts’ Conversion Compilation
Acceleration [angular]
unit name
symbol
SI equiv.
revolutions per square second
rps2
1 rps2
revolutions per square minute
rpm2
2.77778e-04 rps2
radian per square second
rads2
1.59155e-01 rps2
unit name
symbol
SI equiv.
centimeters per square second
cm/s2
1e-02 m/s2
meter per square second
m/s2
1 m/s2
foot per square second
ft/s2
3.048e-01 m/s2
Acceleration [generic]
gravitational accelaration
galileo
g
Gal
9.80665 m/s2
i
1e-02 m/s2
i
Area
unit name
symbol
SI equiv.
square centimeter
cm2
1e-04 m2
square meter
m2
1 m2
are
are
1e+02
m2
hectare
ha
1e+04 m2
square kilometer
km2
1e+06 m2
i
square inch
inch2
6.4516e-04 m2
i
square foot
ft2
9.2903e-02 m2
square yard
yard2
8.36127e-01 m2
i
9.2903
m2
i
2.52929e+01
m2
square
sq
square rod
rd2
i
rood
rood
1.01171e+03 m2
i
acre
ac or A
4.04686e+03 m2
i
6.47497e+05
m2
i
2.58999e+06
m2
homestead
square mile
section
township
homestead
mile2
(int)
sec
2.58999e+06 m2
i
twp
m2
i
9.32396e+07
1
Density [Mass]
unit name
symbol
SI equiv.
kilogram per cubic meter
kg/m3
1 kg/m3
gram per cubic centimeter
g/cm3
1e+03 kg/m3
pound per cubic foot
lb/ft3
1.60185e+01kg/m3
pound per cubic inch
lb/inch3
2.76799e+04kg/m3
grains per cubic foot
grains/ft3
2.28835e03 kg/m3
Density [Molar]
unit name
symbol
SI equiv.
mol per cubic meter
mol/m3
1 mol/m3
kilomol per cubic meter
kmol/m3
1e+03 mol/m3
poundmol per cubic foot
lbmol/ft3
1.6018e+04mol/m3
mol per liter
mol/l
1e+03 mol/m3
Energy
unit name
joule
Newton meter
symbol
SI equiv.
J
1N•m
i
N•m
1N•m
i
kilojoule
kJ
1e+03 N • m
calorie
cal
4.1868 N • m
i
kilocalorie
kcal
4.1868e+03 N • m
i
British termal unit
Btu
1.05506e+03 N •
m
i
kilowatt hour
kW • h
3.6e+06 N • m
horse power hour
hp • h
2.6845e+06 N • m
foot pound force
ft • lbf
1.35582 N • m
gigajoule
GJ
1e+09 N • m
erg
erg
1e-07 N • m
i
Enthalpy [Mass]
unit name
symbol
SI equiv.
kilojoule per kilogram
kJ/kg
1 kJ/kg
joule per kilogram
J/kg
1e-03 kJ/kg
kcal/kg
4.1868 kJ/kg
calorie per gram
cal/g
4.1868 kJ/kg
British termal units per pound
Btu/lb
2.32601 kJ/kg
kilocalorie per kilogram
2
Enthalpy [Molar]
unit name
symbol
SI equiv.
Joule per mole
J/mol
1 J/mol
Joule per kilomole
J/kmol
1e-03 J/mol
kcal/kmol
4.1868 J/mol
cal/mol
4.1868 J/mol
Btu/lbmol
2.32601 J/mol
kilocalorie per kilomole
calorie per mole
British thermal units per pound mole
kilojoule per mole
kJ/mol
kilocalorie permole
kcal/mol
1e+03 J/mol
4.1868e+03 J/mol
Enthalpy [Volume]
unit name
symbol
SI equiv.
Megajoule per cubic meter
MJ/m3
1 MJ/m3
kilojoule per cubic meter
kJ/m3
1e-03 MJ/m3
british thermal units per gallon
Btu/gal
2.7872e-01 MJ/m3
british thermal units per cubic foot
Btu/ft3
3.72589e02MJ/m3
kilocalorie per cubic meter
kcal/m3
4.1868e-03 MJ/m3
Flowrate [Mass]
unit name
symbol
SI equiv.
kilogram per second
kg/s
1 kg/s
kilogram per hour
kg/hr
2.77778e-04 kg/s
metric ton per day
mto/d
1.15741e-02 kg/s
metric ton per year
mto/yr
3.17098e-05 kg/s
pound per second
lb/s
4.53592e-01 kg/s
pound per hour
lb/hr
1.25998e-04 kg/s
kilogram per minute
kg/min
1.66667e-02 kg/s
pound per minute
lb/min
7.55987e-03 kg/s
unit name
symbol
SI equiv.
kilomole per second
kmol/s
1 kmol/s
kilomole per minute
kmol/min
1.66667e02kmol/s
kilomol per hour
kmol/hr
2.77778e04kmol/s
tonmole per day
tmol/d
1.15741e-
Flowrate [Molar]
3
unit name
symbol
SI equiv.
02kmol/s
poundmole per second
lbmol/s
4.53592e01kmol/s
poundmole per minute
lbmol/min
7.55987e03kmol/s
lbmol/hr
1.25998e04kmol/s
poundmole per hour
Flowrate [Volume]
unit name
symbol
SI equiv.
cubic meter per second
m3/s
1 m3/s
cubic meter per hour
m3/hr
2.77778e-04 m3/s
cubic meter per day
m3/d
1.15741e-05 m3/s
cubic foot per second
ft3/s
2.83168e-02 m3/s
cubic foot per hour
ft3/hr
7.86579e-06 m3/s
cubic foot per day
ft3/d
3.27741e-07 m3/s
US gallon per second
USgal/s
3.78541e-03 m3/s
US gallon per hour
USgal/hr
1.0515e-06 m3/s
US gallon per day
USgal/d
4.38126e-08 m3/s
oil barrel per day
oil bbl/d
1.84013e-06 m3/s
cubic decimeter per second
dm3/s
1e-03 m3/s
liter per minute
l/min
1.66667e-05 m3/s
symbol
SI equiv.
Force
unit name
dyne
dyne - g
cm/s2
1e-05 N
i
1.38255e-01 N
i
Poundal
Poundal
Newton
N
1N
i
pound force
lbf
4.44822 N
i
kilogram force
kgf
9.80665 N
i
Kilo Newton
kN
1e+03 N
Sthene
1e+03 N
i
kip
4.44822e+03 N
i
ton force US
tnf US
8.89644e+03 N
i
ton force UK
tnf UK
9.96402e+03 N
i
Sthene
kip
4
Heat capacity
unit name
symbol
SI equiv.
British thermal unit per pound per
degree farenheit
Btu/(lb • °F)
4.1868e+03 J/(kg
• K)
calorie per gram per degree celcius
cal/(g • °C)
4.1868 J/(kg • K)
colorie per pound per degree celcius
cal/(lb • °C)
9.23031 J/(kg • K)
erg per gram per degree celcius
erg/(g • °C)
1e-04 J/(kg • K)
joule per gram per degree celcius
J/(g • °C)
1e-03 J/(kg • K)
joule per kilogram per kelvin
J/(kg • K)
1 J/(kg • K)
kcal/(kg • °C)
4.1868e+03 J/(kg
• K)
kilojoule per kilogram per kelvin
kJ/(kg • K)
1e+03 J/(kg • K)
megajoule per kilogram per kelvin
MJ/(kg • K)
1e+06 J/(kg • K)
kilocalorie per kilogram per degree
celcius
W • s/(kg • °C)
watt second per kilogram per degree
celcius
1 J/(kg • K)
Heat transfer coefficient
unit name
symbol
SI equiv.
watt per square meter per kelvin
W/(m2
• K)
1 W/(m2 • K)
kilowatt per square meter per kelvin
kW/(m2 • K)
1e+03 W/(m2 • K)
watt per square centimeter per
kelvin
W/(cm2 • K)
1e-04 W/(m2 • K)
kilocalorie per hour per square
meter kelvin
kcal/(hr • m2 • K)
1.163 W/(m2 • K)
calorie per second per square
centimeter kelvin
cal/(s • cm2 • K) 4.1868e+08 W/(m2•
K)
British thermal unit per hour per
square foot per degree farenheit
Btu/(hr • ft2 • °F) 5.67826 W/(m2 • K)
Length
unit name
symbol
SI equiv.
Ångstrom
Å
1e-10 m
micron
μm
1e-06 m
millimeter
mm
1e-03 m
centimeter
cm
1e-02 m
meter
m
1m
kilometer
km
1e+03 m
i
i
line
li
2.11667e-03 m
i
inch
"
2.54e-02 m
i
hand
hand
1.016e-01 m
i
2.01168e-01 m
i
link
link
5
unit name
symbol
SI equiv.
foot
ft
3.048e-01 m
i
yard
yd
9.144e-01 m
i
rod
rd
5.0292 m
i
chain
ch
2.01168e+01 m
i
furlong
fur
2.01168e+02 m
i
mile (statute)
mile
1.60934e+03 m
i
mile (nautical)
nmi, naut mi
1.852e+03 m
i
4.82803e+03 m
i
3.08568025e+16 m
i
league
league
parsec
pc
Mass
unit name
symbol
milligram
mg
1e-06 kg
carat
2e-04 kg
gram
g
1e-03 kg
kilogram
kg
1 kg
i
quintal
1e+02 kg
i
ton (metric)
t
1e+03 kg
atomic unit mass
u
1.66054e-27 kg
i
grain
gr
6.47989e-05 kg
i
dram
dram
1.77185e-03 kg
i
ounce
oz
2.83495e-02 kg
i
pound
lb
4.53592e-01 kg
i
stone
stone
6.35029 kg
i
carat (metric)
quintal
Quarter
SI equiv.
i
Quarter
1.27006e+01 kg
hundredweight US
hundredweight US
4.53592e+01 kg
i
Hundredweight UK
Hundredweight
UK
5.08023e+01 kg
i
USton
Uston
9.07185e+02 kg
i
UKton
Ukton
1.01605e+03 kg
i
unit name
symbol
SI equiv.
kilomole
kmol
Moles
poundmole
mol
milli mol
lbmole
mol
mmol
1e+03 mol
4.53592e+02 mol
1 mol
i
1e-03 mol
6
Power
unit name
symbol
SI equiv.
joule per second
J/s
1 J/s
watt
W
1 J/s
kilowatt
kW
1e+03 J/s
megawatt
MW
1e+06 J/s
kilojoule per hour
kJ/hr
2.77778e-01 J/s
i
kgf • m/s
9.80665 J/s
calorie per second
cal/s
4.1868 J/s
calorie per hour
cal/hr
1.163e-03 J/s
British thermal units per second
BTU/s
1.05506e+03 J/s
British thermal units per hour
BTU/hr
2.93072e-01 J/s
Ton (RT)
3.51687e+03 J/s
i
pk (Metric hp)
7.35499e+02 J/s
i
kilogram force meter per second
tons
metric horse power
horse power
hp
7.457e+02 J/s
i
electric horse power
ehp
7.46e+02 J/s
i
boiler horse power
bhp
9.8095e+03 J/s
i
lbf • ft/s
1.35582 J/s
i
symbol
SI equiv.
pound force foot per second
Pressure
unit name
pascal
Pa
1 Pa
kilopascal
kPa
1e+03 Pa
newton per square meter
N/m2
1 Pa
dyne per square centimeter
bar
millibar
dyne/cm2
1e-01 Pa
Bar
1e+05 Pa
mBar
1e+02 Pa
i
i
kgf/cm2
9.80665e+04 Pa
atmosphere
atm
1.01325e+05 Pa
i
pound per square inch
psi
6.89476e+03 Pa
i
meter of water @ 4°C
m H2O 4°C
9.80665e+03 Pa
centimeter of water @ 4°C
cm H2O 4°C
9.80665e+01 Pa
foot of water @ 4°C
ft H2O 4°C
2.98907e+03 Pa
inch of water @ 4°C
inch H2O 4°C
2.49089e+02 Pa
millimeter of mecury @ 0°C
mm Hg 0°C
1.33322e+02 Pa
inch of mercury @ 0°C
inch Hg 0°C
3.38639e+03 Pa
kilogram force per square
centimeter
i
7
Specific heat [Mass]
unit name
symbol
SI equiv.
joule per kilogram per kelvin
J/(kg • K)
1 J/(kg • K)
kilojoule per kilogram per kelvin
kJ/(kg • K)
1e+03 J/(kg • K)
calorie per gram per degree celcius
cal/(g • °C)
4.1868e+03 J/(kg
• K)
kilocalorie per gram per degree
celcius
kcal/(g • °C)
4.1868 J/(kg • K)
British thermal unit per pound mass
per degree farenheit
Btu/(lbm • °F)
4.1868e+03 J/(kg
• K)
cal/(g • K)
4.1868e+03 J/(kg
• K)
calorie per gram per kelvin
Specific heat [Molar]
unit name
symbol
SI equiv.
joule per kilomol per kelvin
J/(kmol • K)
1 J/(kmol • K)
kilojoule per kilomol per kelvin
kJ/(kmol • K)
1e+03 J/(kmol • K)
kilocalorie per kilomol per kelvin
kcal/(kmol • K) 4.1868e+03J/(kmol
• K)
calorie per kilomol per kelvin
cal/(kmol • K)
British thermal unit per poundmol
per degree farenheit
4.1868e+03J/(kmol
• K)
Btu/(lbmol • °F) 4.1868e+03J/(kmol
• K)
Thermal conductivity
unit name
symbol
SI equiv.
British thermal unit per foot per
second per degree farenheit
Btu/(ft • s • °F) 6.23065e+03 W/(m
• K)
cal per second per meter per
degree celcius
cal/(s • m • °C)
4.1868 W/(m • K)
kilocalorie per hour per meter per
kelvin
kcal/(hr • m • K)
1.163 W/(m • K)
joule per second per degree celcius
J/(s • m • °C)
1 W/(m • K)
kilojoue per hour per meter per
kelvin
kJ/(hr • m • K)
2.77778e-01 W/(m
• K)
megawatt per meter per kelvin
MW/(m • K)
1e+06 W/(m • K)
kilowatt per meter per kelvin
kW/(m • K)
1e+03 W/(m • K)
watt per meter per kelvin
W/(m • K)
1 W/(m • K)
watt per centimeter per kelvin
W/(cm • K)
1e-02 W/(m • K)
watt per foot per degree farenheit
W/(ft • °F)
5.90551 W/(m • K)
watt per inch per degree farenheit
W/(inch • °F)
1.41111e-02 W/(m
• K)
8
Time
unit name
symbol
second
s
minute
min
SI equiv.
1s
e = exponent
6 X 101 = 60
6e+01 s
hour
hr
3.6e+03 s
day
d
8.64e+04 s
year
yr
3.1536e+07 s
3.6 X 103 = 3600
Velocity [angular]
unit name
symbol
SI equiv.
degrees per minute
°/min
2.90888e-04 rad/s
degrees per second
°/s
1.74533e-02 rad/s
radian per minute
rad/minute
1.66667e-02 rad/s
radian per second
rad/s
1 rad/s
revolutions per minute
rpm
1.0472e-01 rad/s
revolutions per second
rps
6.28319 rad/s
2.90888 x 10 -4 = .000290888
Velocity [linear]
unit name
symbol
SI equiv.
centimeter per second
cm/s
1e-02 m/s
meter per second
m/s
1 m/s
kilometer per second
km/s
1e+03 m/s
kilometer per hour
km/hr
2.77778e-01 m/s
foot per second
ft/s
3.048e-01 m/s
foot per hour
ft/hr
8.46667e-05 m/s
inch per second
inch/s
2.54e-02 m/s
knot
knot
5.14444e-01 m/s
mile per hour
mph
4.4704e-01 m/s
speed of light in vacuum
Mach
(speed of light in
vacuum) m/s
M
2.99792e+08 m/s
i
3.316e+02 m/s
i
Viscosity [Dynamic]
unit name
symbol
SI equiv.
pascal second
Pa • s
1 Pa • s
millipascal second
centipoise
mPa • s
1e-03 Pa • s
cP
1e-03 Pa • s
9
unit name
symbol
s/m2
kilogram force second per square
meter
kgf •
pound force second per square foot
lbf • s/ft2
SI equiv.
9.80665 Pa • s
4.78803e+01 Pa •
s
pounf mass per foot second
lbm/(ft • s)
1.48816 Pa • s
kilogram per (meter second)
kg/(m • s)
1 Pa • s
gram per (centimeter second)
g/(cm • s)
1e-01 Pa • s
P
1e-01 Pa • s
Poise
i
Velocity [linear]
unit name
symbol
SI equiv.
centimeter per second
cm/s
1e-02 m/s
meter per second
m/s
1 m/s
kilometer per second
km/s
1e+03 m/s
kilometer per hour
km/hr
2.77778e-01 m/s
foot per second
ft/s
3.048e-01 m/s
foot per hour
ft/hr
8.46667e-05 m/s
inch per second
inch/s
2.54e-02 m/s
knot
knot
5.14444e-01 m/s
mile per hour
mph
4.4704e-01 m/s
speed of light in vacuum
Mach
(speed of light in
vacuum) m/s
M
2.99792e+08 m/s
i
3.316e+02 m/s
i
Viscosity [Dynamic]
unit name
symbol
SI equiv.
pascal second
Pa • s
1 Pa • s
millipascal second
centipoise
mPa • s
1e-03 Pa • s
cP
1e-03 Pa • s
kilogram force second per square
meter
kgf • s/m2
pound force second per square foot
lbf • s/ft2
9.80665 Pa • s
4.78803e+01 Pa •
s
pounf mass per foot second
lbm/(ft • s)
1.48816 Pa • s
kilogram per (meter second)
kg/(m • s)
1 Pa • s
gram per (centimeter second)
g/(cm • s)
1e-01 Pa • s
P
1e-01 Pa • s
Poise
i
10
Viscosity [Kinematic]
unit name
symbol
SI equiv.
cSt
1e-06 m2/s
square centimeter per second
cm2/s
1e-04 m2/s
square foot per hour
ft2/hr
2.58064e-05 m2/s
square foot per second
ft2/s
9.2903e-02 m2/s
square meter per hour
m2/h
2.77778e-04 m2/s
square meter per hour
m2/s
1 m2/s
centistokes
stokes
St
1e-04 m2/s
i
Volume
unit name
symbol
milliliter
ml
SI equiv.
1e-06 m3
i
m3
i
l
1e-03 m3
i
cubic decimeter
dm3
1e-03 m3
cubic meter
m3
1 m3
i
1.63871e-05
m3
i
2.83168e-02
m3
cm3
cubic centimeter
liter
1e-06
cubic inch
inch3
cubic foot
ft3
cubic yard
yard3
7.64555e-01 m3
US gallon
US gal
3.78541e-03 m3
UK gallon
UK gal
4.54609e-03 m3
bbl US petrol
1.58987e-01 m3
UK pint
5.68262e-04 m3
barrel US petrol
UK pint
Solar System Reference
Moon:
Mass = 7.36 x 1022 kg
Mean radius = 1.74 x 106 m
11
Our Solar System
Body Order:
Sun.Mercury.Venus.Earth.Mars.Jupiter.Saturn.Uranus.Neptune.Pluto
Sun:
Mercury:
Venus:
Earth:
Mars:
Mass = 1.99 x 1030 kg
Mean radius = 6.96 x 108 m
Mass = 3.18 x 1023 kg
Mean radius = 2.43 x 106 m
Period = 7.60 x 106 s
Distance from Sun = 5.79 x 1010 m
Mass = 4.88 x 1024 kg
Mean radius = 6.06 x 106 m
Period = 1.94 x 107 s
Distance from Sun = 1.08 x 1011 m
Mass =
Mean radius =
Period =
Distance from Sun =
5.98 x 1024 kg
6.37 x 106 m
3.156 x 107 s
1.496 x 1011 m
Mass = 6.42 x 1023 kg
Mean radius = 3.37 x 106 m
Period = 5.94 x 107 s
Distance from Sun = 2.28 x 1011 m
Jupiter:
Mass = 1.90 x 1027 kg
Mean radius = 6.99 x 107 m
Period = 3.74 x 108 s
Distance from Sun = 7.78 x 1011 m
Saturn:
Mass = 5.68 x 1026 kg
Mean radius = 5.85 x 107 m
Period = 9.35 x 108 s
Distance from Sun = 1.43 x 1012 m
Uranus:
Mass = 8.68 x 1025 kg
Mean radius = 2.33 x 107 m
Period = 2.64 x 109 s
Distance from Sun = 2.87 x 1012 m
Neptune:
Mass = 1.03 x 1026 kg
Mean radius = 2.21 x 107 m
Period = 5.22 x 109 s
Distance from Sun = 4.50 x 1012 m
12
Pluto:
Mass = 1.4 x 1022 kg
Mean radius = 1.5 x 106 m
Period = 7.82 x 109 s
Distance from Sun = 5.91 x 1012 m
Other Unit Conversions
Length
1 in
= 2.54 cm
= 0.0254 m
1 ft
= 30.48 cm
= 0.3048 m
1 yard = 91.44 cm
= 0.9144 m
1 mile = 1.6093 Km = 1609.3 m
Area
1 in2
= 6.4516 cm2
1 ft2
= 0.0929 m2
1 acre = 0.4047 hectares = 4047 m2
Volume
1 in3
= 16.387 cm3
1 ft3
= 0.0283 m3
1 us f.oz = 29.574 ml
1 imp f.oz = 28.41 ml
1 us gal
= 3.7854 l
1 imp gal = 4.546 l
Weight
1 OZ
= 28.35 g
1 lb
= 0.4536 kg = 453.6 g
1 imp ton = 1016 kg
Temperature
oF
= oC*1.8 + 32
oC
= (oF - 32) / 1.8
oR
= oF + 459.67
K = oC + 273.15
Time Conversion
COORDINATED UNIVERSAL TIME (UTC) = ZULU TIME CONVERSION CHART TO LOCAL TIME
LOCAL
EDST
MIDNIGHT 0400
1 AM
0500
2 AM
0600
3 AM
0700
EST
0500
0600
0700
0800
CDST
0500
0600
0700
0800
CST
0600
0700
0800
0900
MDST
0600
0700
0800
0900
MST
0700
0800
0900
1000
PDST
0700
0800
0900
1000
PST
0800
0900
1000
1100
13
4 AM
5 AM
6 AM
7 AM
8 AM
9 AM
10 AM
11 AM
NOON
1 PM
2 PM
3 PM
4 PM
5 PM
6 PM
7 PM
8 PM
9 PM
10 PM
11 PM
LOCAL
0800
0900
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
2100
2200
2300
2400
0100
0200
0300
EDST
0900
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
2100
2200
2300
2400
0100
0200
0300
0400
EST
0900
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
2100
2200
2300
2400
0100
0200
0300
0400
CDST
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
2100
2200
2300
2400
0100
0200
0300
0400
0500
CST
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
2100
2200
2300
2400
0100
0200
0300
0400
0500
MDST
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
2100
2200
2300
2400
0100
0200
0300
0400
0500
0600
MST
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
2100
2200
2300
2400
0100
0200
0300
0400
0500
0600
PDST
1200
1300
1400
1500
1600
1700
1800
1900
2000
2100
2200
2300
2400
0100
0200
0300
0400
0500
0600
0700
PST
LEGEND:
EDST = EASTERN DAYLIGHT SAVING TIME
EST = EASTERN STANDARD TIME
CDST = CENTRAL DAYLIGHT SAVING TIME
CST = CENTRAL STANDARD TIME
MDST = MOUNTAIN DAYLIGHT SAVING TIME
MST = MOUNTAIN STANDARD TIME
PDST = PACIFIC DAYLIGHT SAVING TIME
PST = PACIFIC STANDARD TIME
14
How Distances are Measured in Astronomy
Dealing with the numbers involved with the distances to the stars or even with those found in the
solar system can be hard going. Astronomers make their lives easier by using a number of rulers
(units of distance) for the distances and although they have some strange names they can be very
useful for comparing the distances to stars, other galaxies and even the planets in our solar system.
AU (astronomical units)
One AU is the distance that the average distance that the Earth orbits the Sun at. The AUis most
commonly used for the distances of objects with in our solar system. Pluto, the last planet in the
solar system is found at an average distance of 39.47 au from the Sun. Sedna the new body nearly
as large as a planet found beyond Pluto is never nearer to the Sun than 76AU and then goes to
880AU from the Sun in its giant elliptical orbit.
Light Years
One of the most common rulers is the light year. The light year is is the distance that light travel in
one year (365 1/4 days). It is most commonly used for the distances to stars and other galaxies.
The nearest star is 4.2 light years away from our sun. We are 8.3 light minutes away form the Sun.
the distance to the outer most planet Pluto is about 13 light hours.
Some other interesting distances in light years:
Object
Distance in light years
Nearest Star (Proxima Centuri)
4.2
Sirius the dog star (the brightest star in the sky)
8.6
centre of the galaxy
approximately 30 000
Andromeda (one of our nearest neighbouring galaxies)
approximately 2 million
The stars of Orion. (Betelgeuse and Rigel)
1400 light years
Parsec (pc)
Astronomers started measuring distances from the amount that a star moves as the Earth goes from
one side of the Sun to the other. Try moving your head and you will see that the postion of
everything around you changes. One parsec is derived from the smallest angle measurement of
1/3,600th of a degree or an arc second that is the angle that a star at this distance would appear to
move in 6 months as the Earth journeys around the Sun. A parsec is 3.2616 light years or
30,857,000,000,000 km.. Two parsecs is 6.5532 light years or twice the distance, it is not a measure
of change in angles of the stars. Due to the massive distance in the universe astronomers often use
multiples of parsec commonly found are kiloparsec (kpc) a 1000 parsecs or a megaparsec (Mpc)
1,000,000 parsecs.
15
Below is a conversion table for some useful astronomical distance units
kilometres
(km)
kilometres (km)
Astronomical
Light Years (l.y.) Parsec (pc)
units (AU)
1
149.6 million 9,460,000,000,000 30,857,000,000,000
Astronomical
0.0000000067
units (AU)
1
63,240
206,263
Light Years
(l.y.)
0.00000000000011 0.000016
1
3.2616
Parsec (pc)
0.000000000000033 0.0000048
0.3066
1
16