Measuring Universal Distances

What is a Light Year?In the beginning of every Star Trek episode, (the original and Next generation), the Enterprise shoots out into space at light speed once warp drive is initiated. Ever notice the stars are moving along with it? In reality, this could not be possible, as the stars are so far away from each other and the Enterprise, (actually trillions and quadrillions – the number 1 followed by 15 zeros) of miles apart, that they still would not be moving at all and should be displayed as stationary.

How Do We Calculate Vast Distances in Space?

When discussing and calculating the vast distances of the universe, we must utilize this unit of time. This is because using numbers such as 100,000,000,000,000,000 (100 quadrillion) would be counterproductive.  More time would be spent calculating the math than focusing on the science; hence, we discuss distance with corresponding units of time, such as the light year and astronomical unit.

What is the Unit that is Used to Measure Distances in Outer Space?

Enter light years. The speed of light is 186,000 miles per second and, according to Einstein, no one can go faster than the speed of light. The distance for light to travel in one year is approximately 4 trillion miles, so if you were in a spaceship moving at 50,000 miles per hour, it would take you about 40,000 years to travel one light year.

Another example: The distance between Earth and the star Alpha Centauri is 4.3 light years. If you were traveling at the speed of light, it would take you 4.3 years to get to Alpha Centauri or if you were travelling in the space ship at 50,000 miles per hour, it would take you 172,000 years to get there. 

Using light years to determine distances to other galaxies is even more convenient, considering the vast distances they are from our Milky Way galaxy.  One of our closest neighboring Galaxy – the Andromeda Galaxy is 220,000 light years from earth, so in a spaceship travelling at warp speed (speed of light), it would still take you 220,000 years to get there.

Some additional examples depicting the distances of objects in space from Earth are:

Barnard’s Star: 6.0 light years.
To determine how far this is in miles, you would need to multiply 60 (seconds) x 60 (minutes) x 24 (hours) x 365 (days) x 6.0.

Betelgeuse, the second brightest star in the constellation Orion is 600 light years from Earth.

The length of the Milky Way galaxy is approximately 120,000 light years across.

The Large Magellanic Cloud is 179,000 light years away.

The galaxy Andromeda is 2.5 million light years.

The galaxy MACS0647-JD is 13.3 billion light-years away.

The known distance of the universe has been calculated to be about 13.3 billion light-years away from Earth.

To give some additional perspective to this, if we stated the distance of MACS0647-JD from our solar system instead of from Earth, it would still be listed as 13.3 billion light-years away. Even if we stated the distance of MACS0647-JD our Milky Way galaxy, the distance would not change. This is because the distance calculated between these objects mentioned would be so minuscule, it would not matter when discussing how far it is. (Of course, when scientists measure these distances for research, the numbers would have to be exact and there would be a slight change in the measurements, but not enough for discussion here).

What is an Astronomical Unit?

The astronomical unit (AU) is the distance between Earth and the Sun, so for small distances we can use AU instead of light years. If an object is 400,000,000 miles from Earth, we can say that this object is approximately 4 AUs, since Earth’s distance from the sun is 93,000,000 miles.

When you look at the sun (not recommended), you are actually looking at it nine minutes earlier, because it takes its light nine to reach earth. Therefore, if the sun exploded right now, you still have nine minutes to live.