David Cater/Star-Gazing Pictured is spiral galaxy M101, just one of billions to be seen in April.Pun intended: March was a washout! Too many days of rain and clouds for amateur astronomy. I am hoping in April and May, to see the sky again for some longer periods and I hope to make more photographs of interesting things in the night sky.
April is a good time to see galaxies if you have a capable telescope. Even if you don’t have a telescope, perhaps you can find an amateur and he/she might show you some of them. By the way, amateur astronomy is one of the fastest growing hobbies among women. We may also be able to see a naked-eye comet, Comet Atlas, in May, if it doesn’t break up on its way around the Sun. I will keep you posted.
I want to devote most of this column to galaxies.
As the Earth moves along its orbit around the Sun, we will see off the plane of the Milky Way and very far out into deep space. This happens in April and May and this allows even amateurs, with large enough telescopes, to see many of these very remote objects.
Galaxies are the largest physical systems we know of and they have been viewed from about the time the telescope was invented — the 1600s. As telescopes got bigger and photography was developed, it became possible, by about the 1930s, to examine a large number of good images of galaxies, taken with large telescopes and fast photographic plates.
Edwin Hubble, working with the 100-inch reflector atop Mt. Wilson, Calif., was able to make the first classification system of galaxies. Hubble classified galaxies by their shapes. In any science, it is always useful to know whether or not the things that are studied in that science fall into a natural classification. If these phenomena do fall into a natural system, then it becomes possible to work on the problem of why this happens. When it came to studying galaxies, the science of these galaxies advanced hugely because of the ability to classify them and then to ask why these shapes?
On the basis of galactic shapes, Hubble found three natural classes: Irregular galaxies, Elliptical galaxies and Spiral Galaxies. A fourth class, Lenticular galaxies, has since been added, as well as many subclasses. Irregular galaxies are irregular with no particular shape; Elliptical galaxies are round or egg-shaped; and Spiral galaxies often look like enormous pinwheels. Lenticular galaxies have relatively well-defined edges and look like double convex lenses. All galaxies rotate through a spin axis and this rotation can take millions of years.
How many galaxies are there? It is impossible to get an accurate count but certainly there are billions of them! The so-called Hubble Deep Field, an image made over several days of a very small patch of sky, revealed approximately 1,500 of them on one plate!
How far away are galaxies? The closest one to us is about 2.5 million light-years away. Today, we can get good images of galaxies we know lie billions of light years away.
Our own galaxy, the Milky Way, is a spiral galaxy about 100,000 to 120,000 light-years across. It is difficult to get an exact measurement when you live in the galaxy you are trying to measure, and most galaxies do not have exact, sharply-defined edges. Our Solar System lies out in one of the spiral arms of the Milky Way, about 23,000 light years from the core.
As far as we can tell by examining the images we can get, the presentation angles of the galaxies are random with respect to us. We see some face-on, we see some edge-on, but the great majority of them are seen at random angles. I have included an image of a large face-on spiral galaxy, M101, that I made with the telescope at JBU. As you can see, this one has beautiful spiral arms, extending thousands of light years from the center. This galaxy is visible this time of year and amateur telescopes can reach it.
Comet Atlas is in-bound towards our Sun now, and it will pass behind the Sun in April and, hopefully, emerge as a naked-eye apparition. It could melt and break up because of the Sun’s heat but at this point, no one knows for sure.
There are always wonders to be seen — keep looking at the night sky.
— Dr. David Cater is a former faculty member of JBU. Email him at starbug352@yahoo.com. The opinions expressed are those of the author.
Community on 04/01/2020
