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The term **parsec** is a portmanteau of "parallax second" and it is a unit of distance used in astronomy. To understand what a parsec is, we delve into the concept of stellar parallax, a method used to measure the distances to the stars. When you see an object from two different places, it might appear to be in a different location relative to its background. This is called parallax.
Astronomers measure the angle of apparent shift in a star’s position over six months, as Earth orbits around the Sun. A parsec is defined as the distance at which one astronomical unit (AU) subtends an angle of one arcsecond. It is an immense distance amounting to about 3.262 light years. Consequently, when stars are said to be certain parsecs away, they are truly far.

• 1 parsec = 3.262 light years
• Name derived from: parallax second
• Used to measure astronomical distances

Since the parsec represents such vast distance, it is commonly used for distances within our galaxy or to other galaxies to ease in calculations and understanding of the vast universe.

When dealing with astronomical distances, it is often necessary to convert between units like parsecs and light years to make sense of the scale.
For the exercise, we had to convert 85 parsecs into light years, because light years is a more intuitive way of understanding the time it would take light to travel a given distance. Since 1 parsec is equivalent to 3.262 light years, converting parsecs to light years is done by multiplying the number of parsecs by 3.262.
Here's how it works:

• Identify distance in parsecs
• Multiply by 3.262 to convert to light years

For example, the given solution showed 85 pc translates to approximately 277.27 light years by calculating:\[ 85 \times 3.262 = 277.27 \text{ light years} \] Having distances in light years will allow us to intuitively understand how many years light takes to cross these distances in space.

The concept of **light travel time** provides us a glimpse into the immense scales of the universe. Light year is not just a distance measure, but it corresponds directly to the time light takes to travel through the vacuum of space in one Earth year.
This implies that if a star is located 277.27 light years away, it takes light emitted from that star 277.27 years to reach Earth. Hence, when we look at distant stars or galaxies, we are essentially seeing them as they were in the past. The light travel time allows astronomers to look back in time and understand the universe's history.

• 1 light year is the distance light covers in one year.
• Time taken = Distance in light years
• Great tool for observing cosmic history

In the given exercise, 277.27 light years also means the light from the star started its journey towards us 277.27 years ago.