Astronomical distances
distanceNumerical description of how far apart two things are. For example, the distance from Edinburgh to Glasgow is approximately 50 miles. in space are vast. If we measure them in miles or kilometer (km)1000m. A large unit for distance. In Physics, distance is measured in metres (m). the numbers would very large, eg the distance from Earth to the Sun is 150 million kilometres (\(150,000,000 km\)).
Outside of the Solar System distances are even greater so we use a measurement of distance called the light yearThe distance travelled by light in one year - a very large distance, usually used to describe distances between stars. The closest star to our own is about 4.3 light years away..
The light year
Distances in space are so enormous so it is more appropriate to use the light year as the unit of distance. We know light travels a distance of 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 \(3 \times m\,s^{-1}\)) so in one year it will cover a distance of \(9.47 \times 1015\) metres.
One light year is the equivalent distance light travels in one year. Other than the Sun the nearest star to us is Proxima Centauri which is 4.2 light years from Earth. Light from our Sun takes only 8 minutes to reach us.
Calculating the speed of light