Megaparsec to Light-Year Converter

How it is calculated

The conversion uses one fixed factor, 1 Mpc = 3,261,563.7 ly. Going from megaparsecs to light-years, ly = Mpc × 3,261,563.7. Going the other way, with the direction set to light-years to megaparsecs, Mpc = ly ÷ 3,261,563.7. The light-year result is shown with one decimal and the megaparsec result with six. The page also shows the factor used and the reverse conversion as a check. The value cannot be negative. Any direction value other than the light-year to megaparsec option is treated as megaparsec to light-year. The factor is a rounded figure, so very large distances carry the same relative rounding.

Common mistakes

• Leaving the direction on megaparsec to light-year when you are entering light-years. Typing 2,500,000 would then give a result in the trillions of light-years instead of about 0.77 Mpc.
• Confusing megaparsecs with parsecs or kiloparsecs. One Mpc is a million parsecs, so a distance given in pc must be divided by 1,000,000 first.
• Typing the number with a thousands separator, as in 2,500,000. Enter plain digits and a decimal point so the value is read correctly.
• Treating a light-year distance to a faraway galaxy as the distance today. Light left it that long ago, and in an expanding universe the object is farther away now.
• Entering a negative distance. The tool does not accept it and shows nothing.