Video: Converting between Light-Years and Megalight-Years

Astronomers often measure the distance to faraway galaxies in units of megalight-years. What is the unit symbol for a light-year? What is the unit symbol for a megalight-year? How many light-years are there in a megalight-year?

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Video Transcript

Astronomers often measure the distance to faraway galaxies in units of megalight- years? What is the unit symbol for a light-year?

Now, a light-year is the distance travelled by light in one year. But in this question, we’ve been asked to give the unit symbol for a light-year. And the way to remember this is that a light-year is abbreviated ly for light-year. And so that’s our answer to this part of the question. The unit symbol for a light-year is ly. It’s important to remember though that both the l and the y need to be in lowercase. And hence the unit symbol for a light-year is lowercase l and lowercase y.

Moving onto the next question then, what is the unit symbol for a megalight-year?

Now, the unit symbol for a megalight-year is the unit symbol for a light-year but with the prefix mega in front of it. But we need to remember that the M representing mega has to be capitalised, because if we were to write lowercase mly, then this would represent millilight-years since lowercase m represents the prefix milli. But anyway, so our answer to this part of the question is that the unit symbol for a megalight-year is capital M, lowercase l, lowercase y.

Now, the next part of the question asks us how many light-years are there in a megalight-year?

To answer this question, we need to recall that one megalight-year is equal to one times 10 to the power of six light-years because the prefix mega represents 10 to the power of six. This is something that we just need to memorize. And there’re lots of other prefixes as well. But in this case, the prefix mega represents 10 to the power of six, which is the same thing as 1000000. And so hence, we can say that one megalight-year is equal to 1000000 light-years.

And because they’re equal, our final answer is that there’re 1000000 light-years in a megalight-year.

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