How to Calculate a Light Year
Define the light year., Write the formula for distance., Define the speed of light., Calculate the number of seconds in a year., Plug variables into equation and solve., Calculate the distance in kilometers.
Step-by-Step Guide
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Step 1: Define the light year.
A light year is a measure of distance equal to how far light travels in one Earth year.
Because distances across the universe are so large, astronomers use light years.
Without light years, discussing the distance between two stars would require the use of large, unruly numbers.Another measure of distance you may come across when learning astronomy is the parsec.
It is equal to
3.26 light years.
It is another way to simplify the numbers used to calculate and discuss astronomical distances. -
Step 2: Write the formula for distance.
Using the common physics formula, distance equals rate times time or d = r x t, you can calculate how long a light year is:
Light Year = (speed of light) x (one year).
Since speed of light is represented by the variable “c”, you can rewrite the equation as d = c x t, where d is the distance of a light year, c is the speed of light and t is time.If you want to know the distance of a light year in kilometers, you will need to find the speed of light in kilometers per second.
If you want miles, you will need the speed of light in miles per second.
You need to know the number of seconds in one Earth year for this calculation. , Light in a vacuum travels at a velocity of 186,000 miles per second.
This is the equivalent of 299,792 kilometers per second or 670,616,629 miles per hour.Here we will use the velocity in miles-per-second.
For this calculation we will use the speed of light, c, equals 186,000 miles per second.
This can be rewritten in scientific notation as
1.86 x 105 miles per second. , To find the number of seconds in a year, you will do a series of multiplications by conversions units.
To convert years to seconds you will multiply the number of days in a year times the number of hours in a day, times the number of minutes in an hour, times the number of seconds in a minute. 1 year x 365 days/year x 24 hours/day x 60 minutes/hour x 60 seconds/minute = 31,536,000 seconds.Again, we can rewrite this large number using scientific notation as
3.154 x
107. , Now that you have defined the variables for speed of light and time, you can plug them into the equation d = c x t and solve for the distance of a light year.
Replace c with
1.86 x 105 miles per second and time with
3.15 x 107 seconds.d = c x t d = (1.86 x 105) x (3.154 x 107 seconds) d =
5.8 x 1012 or
5.8 trillion miles. , If you wanted to calculate in kilometers, simply replace the speed of light with the speed in kilometers per second:
3.00 x
105.
The time in seconds remains the same because there is no conversion required.d = c x t d = (3.00 x 105) x (3.154 x 107 seconds) d =
9.46 x 1012 or
9.5 trillion kilometers. -
Step 3: Define the speed of light.
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Step 4: Calculate the number of seconds in a year.
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Step 5: Plug variables into equation and solve.
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Step 6: Calculate the distance in kilometers.
Detailed Guide
A light year is a measure of distance equal to how far light travels in one Earth year.
Because distances across the universe are so large, astronomers use light years.
Without light years, discussing the distance between two stars would require the use of large, unruly numbers.Another measure of distance you may come across when learning astronomy is the parsec.
It is equal to
3.26 light years.
It is another way to simplify the numbers used to calculate and discuss astronomical distances.
Using the common physics formula, distance equals rate times time or d = r x t, you can calculate how long a light year is:
Light Year = (speed of light) x (one year).
Since speed of light is represented by the variable “c”, you can rewrite the equation as d = c x t, where d is the distance of a light year, c is the speed of light and t is time.If you want to know the distance of a light year in kilometers, you will need to find the speed of light in kilometers per second.
If you want miles, you will need the speed of light in miles per second.
You need to know the number of seconds in one Earth year for this calculation. , Light in a vacuum travels at a velocity of 186,000 miles per second.
This is the equivalent of 299,792 kilometers per second or 670,616,629 miles per hour.Here we will use the velocity in miles-per-second.
For this calculation we will use the speed of light, c, equals 186,000 miles per second.
This can be rewritten in scientific notation as
1.86 x 105 miles per second. , To find the number of seconds in a year, you will do a series of multiplications by conversions units.
To convert years to seconds you will multiply the number of days in a year times the number of hours in a day, times the number of minutes in an hour, times the number of seconds in a minute. 1 year x 365 days/year x 24 hours/day x 60 minutes/hour x 60 seconds/minute = 31,536,000 seconds.Again, we can rewrite this large number using scientific notation as
3.154 x
107. , Now that you have defined the variables for speed of light and time, you can plug them into the equation d = c x t and solve for the distance of a light year.
Replace c with
1.86 x 105 miles per second and time with
3.15 x 107 seconds.d = c x t d = (1.86 x 105) x (3.154 x 107 seconds) d =
5.8 x 1012 or
5.8 trillion miles. , If you wanted to calculate in kilometers, simply replace the speed of light with the speed in kilometers per second:
3.00 x
105.
The time in seconds remains the same because there is no conversion required.d = c x t d = (3.00 x 105) x (3.154 x 107 seconds) d =
9.46 x 1012 or
9.5 trillion kilometers.
About the Author
Eric Murphy
Writer and educator with a focus on practical hobbies knowledge.
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