Back to Top

Offbeat Astronomy

Thinking in Metric for Astronomy

This is a chart of metric values to help in understanding the large distances of outer space. Metric is perfect for providing an easy understanding of both absolute and relative distances in astronomy because it provides distance units for every needed scale and an easy way to go up and down the scale.

The most important part of “thinking in metric”, as I call it, is to become familiar with the metric SI prefixes which have matching powers of 10 (all divisible by 3) from section 1. So it is important to know not just kilometers but all of the metric SI distance units for kilometers to yottameters. It is much easier to remember that an Astronomical Unit is 150 gigameters than 1.5 x 108 kilometers or 1.5 x 1011 meters. You probably already know about “mega”, “giga”, and “tera” if you understand computers. You already know kilometers. If you can learn the 8 planets of the solar system, you can learn these 8 metric SI units. Section 2 has the conversion values from metric units into other units like light years, parsecs, and astronomical units. I translate ly to Pm without a calculator by thinking of a ly as 10 Pm – 5%. So 50 ly = (50 * 10 Pm) – 5% = 500 Pm – 5% = 475 Pm. Finally, section 3 is helpful for comprehending most astronomy distances in metric terms.

How long are the metric units for large distances? A megameter is nearly the distance from NYC to Chicago. A gigameter is about 2.5x the distance to the moon. A terameter is about 2/3 of the distance from the Sun to Saturn and light travels at 1.08 terameters per hour. A petameter will get you into the near side of the Oort Cloud. An exameter is 25x the distance to Alpha Centauri. A zettameter is the diameter of our entire galaxy. And a yottameter is the diameter of the Virgo Supercluster which includes our galaxy.

So kilometers and megameters are useful scales for orbital altitudes around planets and lunar distances. Gigameters and terameters are useful scales for planet and solar system object distances. Petameters are useful for interstellar distances. Exameters are useful for larger galaxy structures and very distant stars. Zettameters is a useful scale for understanding distances between galaxies. And yottameters is a useful scale for galactic superclusters and larger structures.

I. Metric Distance Units

II. Conversion to Non Metric Units

III. Metric Distance Values

A. Surface Distances

B. Object Sizes

C. Earth Altitudes

D. Outer Space Distances

Further Reading

See visual pictures of metric distances


Back to Top