What Mars teaches us about the universe

By Tom Burns


If you look high in the WSW just after evening twilight, you’ll see Mars between the horn stars of Taurus, the Bull. Over the coming days, Mars will move farther above the Bull’s horns toward the constellation Gemini.

You can learn two fundamental principles about the universe if you take the trouble to observe the planet and the stars.

The first is that the planets move against a starry background that appears to be fixed in place. As you watch Mars move, you see its orbit around the sun, a motion complicated somewhat by Earth’s motion.

The orbit of Mars carries it around the sun — and thus around the sky — every 1.9 years. The Martian year is nearly twice Earth’s because it is farther from the sun, giving it farther to go to make one trip around old Sol.

The second principle is the three-dimensionality of space. Intellectually, we know the stars and planets aren’t plastered to the bowl of night, but for all practical purposes, it looks and feels like they are.

In short, space has depth.

Elnath, the tip of Taurus’s horn to the right of Mars, shines 700 times brighter than the sun. Mars glows with dim light reflected from the sun.

How can such a puny planet, about 4,000 miles wide, outshine luminous Elnath?

The answer, of course, is the relative distance of the objects.

Earth’s moon makes a good benchmark when considering the distance to astronomical objects. Luna is about a quarter of a million miles away. Its light takes a little over one second to travel to your eyes.

As an astronomer might say, the moon is about one light-second away. You are always seeing the moon the way it looked one second ago.

Mars is currently 120 million miles away, a distance of 10.8 light minutes. You’re seeing Mars the way it looked 10.8 minutes ago because that’s how long it took the light to get to you.

Elnath is about 800 trillion miles away. The light you are seeing took a whopping 134 years to get here.

As you look at Elnath and Mars, you are looking into the depth of space. The light from Mars took about the same time to get here as it takes you to eat a peanut butter and jelly sandwich. The light from Regulus took considerably more than a human lifetime.

We look more deeply into space when we switch our gaze to the constellation Leo, the Lion, and its many galaxies.

Over to the southeast, look for the constellation Leo. Regulus is the pale blue star that forms the front paw of the Lion.

Regulus is about 77 light-years away, about the length of a human lifetime.

When we look at Leo, we can look through a thin cross-section of our own Milky Way galaxy to the galaxies beyond.

The best grouping of those galaxies sits just below the back paw of Leo. This triplet of galaxies called the “Trio in Leo” — M65, M66, and NGC 3628 — is worth a look if you have a telescope or binoculars.

M65 and M66 are pretty easy to see as small fuzzy patches in binoculars. You’ll need a telescope to see NGC 3628.

They will show more detail in a medium-sized or large ‘scope, in which they will all fit into one low-powered field of view. M65 and M66 are small, bright, and close together. M65 is slightly more elongated. The other galaxy, 3628, is long and very narrow. This galactic tableau resembles a ghostly, smiley emoji floating in space, with M65 and M66 forming the eyes and 3628 forming the slightly up-curved smile.

The Trio is over 30 million light-years away or about 180 million trillion miles. That’s around 500,000 times the distance from here to Regulus and the other stars that form the outline of Leo.

Earth was a much different place when the light we see now began its long journey from those distant galaxies. The species called Homo sapiens would not inhabit the planet for another 29.7 million years.

Those faint streaks of light tell us that we exist in a tiny slice of space and time in a universe vast beyond comprehension.

Tom Burns is the former director of the Perkins Observatory in Delaware.