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Cosmology tackles big subjects

Greetings stargazers.

How did we get here? Where are we going? How big and how old is the universe, and what is our place in it? These are some of the big questions that some might argue go beyond scientific investigation and creep into philosophical speculations. But if we can quantify, with uncertainties, any aspect of these big questions, then we are well within the realm of science. This is the field of cosmology; a subject that many of us are curious about.

A significant contribution to astronomy in the early 20th century was that of Edwin Hubble, who observed that more distant galaxies are moving away from us at greater velocities than closer galaxies. He deduced that the universe is not static but is expanding. This expansion was the first hint of the Big Bang, by running time backward to see where things were in the past.

The recession velocity of a distant galaxy is determined from the Doppler shift seen in its spectra. The Doppler shift is just a change in perceived frequency when an emitting object is either moving toward or away from the observer. The classic example to understand Doppler shift, is to listen to the change in pitch from higher to lower frequencies of a train whistle as a speeding train is first approaching you and then receding away from you. (Speeding trains are hard to find in Durango, so it might be best to imaging someone holding down a car horn as they drive past you on the highway.) If you measure the frequency, it is straightforward to calculate the velocity.

During the 1980s, the first of what are called redshift surveys was completed. For these surveys, the redshift, and thus the distance to all visible galaxies in one section of the sky, is measured. These surveys produced the first three dimensional maps of the universe. The most recent surveys give the distances to millions of galaxies.

Besides a nice map of where things are, the surveys support the cosmological principle, which says that the universe is both homogeneous and isotropic. Being homogeneous is like homogenized milk – it simply means things are evenly distributed, or the same, no matter where you are. Being isotropic means the universe looks the same in all directions. There is no preferred center or edge of the universe.

Homogeneous doesn’t mean there isn’t structure in the universe. There are indeed clusters and superclusters of galaxies distributed on what look like the surface of foamy soap bubbles. It is just that the local soap bubbles have the same characteristics as the most distant ones we can see.

Last month, I mentioned the Virgo cluster of galaxies, which is estimated to be between 50 and 60 million light years away. That cluster is part of the Virgo Supercluster, which itself is part of an even larger cluster called Laniakea, which contains about 100,000 galaxies.

This month:

The winter constellations around Orion are quickly setting in the west, and the summer constellations along with the core of the Milky Way are rising later at night.

Venus and Mars are still prominent in the evening sky, and are heading toward a midsummer conjunction.

The Lyrid Meteor Shower peaks on the night of April 22. Although this is only an average shower, it comes only a couple of days after the new moon, so there should be several good days to look for shooting stars.

International Dark Sky week is April 15-22. The International Dark-Sky Association website reminds us that light pollution cannot only block our view of the universe, it can also disrupt wildlife, impact human health, waste money and energy, and contribute to climate change. Please turn off your outside lights and encourage your neighbors to do the same.

Useful links

Redshift Survey


Astronomy picture of the day


An Astronomer’s forecast for Durango


Old Fort Lewis Observatory



Charles Hakes teaches in the physics and engineering department at Fort Lewis College and is the director of the Fort Lewis Observatory.