Measuring the Universe


May 29, 2019

Measuring the Universe


The Universe is vast, but to appreciate the sheer size of the cosmos, a scale model for picturing astronomical distances is used. The best model to use is the one presented by Robert Burnham Jr, of the Lowell Observatory, Dover, New York, in 1978.

In that year, Burnham published the three-volume Celestial Handbook, subtitled "An Observer's Guide to the Universe Beyond the Solar System." It combines an introduction to astronomy with detailed data about the 88 constellations and his scale model, which allows astroscientists to grasp the distances to the stars and other celestial objects:

Burnham's Celestial Handbook

Burnham's model is based on the coincidence that there are 63,360 inches in a mile and 63,294 Astronomical Units (AUs) in a light-year. In other words, on the Burnham scale, a speck two-thousandths of a millimeter across representing the Earth lies one inch away from a speck of dust a hundredth of an inch across representing the Sun.

On this scale, the planet Mercury is four-tenths of an inch from the Sun. Venus is nearly three-quarters of an inch away, Mars is 1.6 inches away, Jupiter is 5 inches away, Saturn is just under 10 inches away, Uranus is at 19 inches, Neptune at 30 inches, and Pluto is at 39.5 inches, or about a yard or a meter.

Another way of picturing the Burnham scale is to stand with an arm outstretched. The tips of the fingers to the center of the body approximates the radial distance of Neptune or Pluto from the Sun.

Alpha Centauri is the nearest star system to the Sun at 4.5 light-years away. On the Burnham scale, it is 4.5 miles away.

As stars in Milky Way are several light-years apart, and with each one represented by a speck of dust on the Burnham scale, each is separated from its nearest neighbors by miles. In other words, they are practically isolated.

The span of the Milky Way Galaxy on this scale is about 100,000 miles. It is enormously big compared with that of the Solar System - 80 inches, compared to 6.336 billion inches. And that is just our galaxy.

The nearest galaxy to ours, the Andromeda Galaxy, is two million light years away. That is two million miles away on the Burnham scale. The Andromeda Galaxy and the Milky Way are members of the Local Group of galaxies. That in itself is connected to galaxy strings and clusters, which are part of galaxy superclusters.

Even on the Burnham scale, the sheer size of the Universe is so great that it is difficult to comprehend. It extends for many millions of miles on the scale. However, at least the scale gives an accurate picture of the extent of the Solar System.

FYI: 1 AU is the mean separation of the Earth from the Sun, which is around 93 million miles. A light year is a distance traveled by light in a vacuum over a one-year interval. Light travels at about 186,000 miles each second, so the distance covered is approximately 186,000 x 24 x 3,600 x 365 = 5.86 x 1012 miles, or roughly 6 trillion miles.