Because distances in space are so great that conventional numbers are too large to work with, astronomers use a unit of measurement called lightyear to measure the distance to stars and galaxies in space.
Light Year
Because distances in space are so great that regular numbers are much too large to work with astronomers use a unit of measurement called light-years to measure the enormous distances to stars and galaxies in space.
- A lightyear is a measure of distance (not time).
- One light year is equal to the distance light travels in one year.
Light travels 186,000 miles in 1 second!
Light travels 6,000,000,000,000 (trillion) miles in one year!!
Even though light travels incredibly fast other celestial objects are so far away from Earth it takes light a long time to reach Earth. For example, it takes light from our own Sun more than 8 minutes just to reach Earth!
How close is the next nearest star to our Sun?
The nearest stars to Earth are in the Alpha Centauri triple-star system, about 4.37 light-years away!
How BIG is our Milky Way Galaxy?
The Milky Way Galaxy is approximately 100,000 light years across and about 1,000 light years thick.
How close is the next nearest galaxy to our galaxy?
A small, irregular galaxy with a mass of about a billion stars, the Canis Major dwarf galaxy is one of our closest neighbours, lying approximately 25,000 light years from the Sun and 42,000 light years from the center of the Milky Way.
When we look out into space are we really looking at the past?!Yes, even light we see from our own Sun is over 8 minutes old! Therefore, when we look up at the stars at night we are looking at light that is years even thousands of years old!
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How exactly do scientists measure such vast distances in space?
Astronomers estimate the distance of nearby objects in space by using a method called stellar parallax. Simply put, scientists measure a star's movement against the background of more distant stars as Earth revolves around the Sun.
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Topic Tips
- Astronomers use a light-years to measure the enormous distances in space.
- A light year is a measure of distance.