The Astronomical Unit, Light Year and Parsec

The Astronomical Unit, Light Year and Parsec

The Astronomical Unit

• The Astronomical Unit (AU) is a measurement unit used in astronomy.
• It’s defined as the average distance from the Earth to the Sun, approximately 93 million miles or about 150 million kilometres.
• This unit is often used when explaining distances within our solar system, offering an easier perspective to understand as opposed to using miles or kilometres.

Light Year

• A light year (ly) is another unit used in astronomy, but it’s a measure of distance that light can travel in one year in the vacuum of space.
• A light year is equivalent to about 5.9 trillion miles or 9.5 trillion kilometres.
• Keep in mind that a light year measures distance, not time. It’s regularly used in the broader field of astronomy when discussing distances outside of our solar system.

Parsec

• The parsec (pc) is a unit of length used in astronomy. It’s equal to about 3.26 light years.
• A parsec is the distance at which one astronomical unit subtends an angle of one arcsecond.
• Parsecs are utilised to measure larger distances at the scale of galaxies, due to their vast size compared to other measurement units.

Comparisons

• The Astronomical Unit is the smallest unit and used for smaller, more local measurements within our solar system.
• Light years are larger and are used for distances outside of our solar system, particularly for measuring distances to other stars within the Milky Way Galaxy.
• Parsecs are the largest of the units and are typically used to describe extremely large distances such as those between galaxies or significant structures within galaxies.

Remembering the scale and application of these three units can be helpful in navigating the sizeable distances and sizes in astronomy.