Measuring distances in space
The distance from the Earth to the Moon (the closest object to us in space) is \(384,000,000 m\). From the Earth to the Sun is \(149,597,871,000 m\).
Astronomical data from observations of galaxies in space involve extremely large distances. The light year is a unit of distance used in astronomy, and it is defined as the distance that light travels in one year.
Light travels 300 million metres in one second (speedThe distance travelled in a fixed time period, usually one second. of light in a vacuumA volume that contains no matter. is \(3\times10^{8}m\,s^{-1}\)). In one year it will cover a distance of \(Distance = 9.46 \times {10^{15}}m\).
After the Sun, the nearest star to us is Proxima Centauri which is 4.2 light years from Earth. Light from our Sun takes approximately eight minutes to reach us.
One light year (distance) can be calculated as follows:
\(Distance = speed \times time\)
\(Distance = 3 \times {10^8} \times (second{\mathop{\rm s}\nolimits} \,in\,one\,year)\)
\(Distance = 3 \times {10^8} \times (60 \times 60 \times 24 \times 365)\)
\(Distance = 9.46 \times {10^{15}}m\)
Calculating the speed of light
Question
The Crab nebula is approximately 6500 light years from Earth.
Calculate this distance in metres.
\(d=v\,t\), \(v=3\,\times10^{8}\), \(t=6500\,years=6500\,\times\,60\,\times\,60\,\times\,24\,\times\,365=2\cdot05\,\times\,10^{11}s\)
\(d=3\,\times\,10^{8}\,\times\,2\cdot 05\,\times\,10^{11}\)
\(d=6\cdot 15\,\times\,10^{19}m\)