The constellation Leo, the lion, is high in the southwest after nightfall. Leo contains over a dozen galaxies that are easily viewed with modest backyard telescopes.
Of those galaxies, the most famous grouping is the Leo Triplet, which consists of NGC 3628, M65 and M66. We don’t always do a great job of naming things in astronomy, and I’ve never understood why this group of galaxies isn’t called the “Leo Trio.” That sure sounds better to my ear, so let’s go with it.
NGC stands for New General Catalog. The “M” designation comes from the Messier catalog, a group of 110 bright astronomical objects observed by French astronomer Charles Messier in the late 1700s.
This list contains a wide variety of different objects, including galaxies, nebulae and star clusters. Many amateur astronomers attempt to view all of these objects — sometimes in a single night during a “Messier marathon.”
Most galaxies are invisible to the naked eye and require optical aid to see. The Leo Trio is just on the edge of binocular range, but to really enjoy it you’ll want a 4-inch or larger telescope.
The three galaxies in the trio are gravitationally bound to each other, and it appears as though there have been some relatively recent interactions between them. The closest galaxy in the group, NGC 3628, is also the dimmest. This edge-on spiral galaxy escaped the notice of Messier, but today we can see an obvious distortion in the disc due to gravitation influence from the other two galaxies in the group.
More powerful telescopes have revealed a tidal tail of stars that’s more than 300,000 light-years long, another result of the gravitational pull of M65 and M66. NGC 3628 is approximately 35 million light years away from us while the most distant member of the group, M65, is about 42 million light years distant.
The three galaxies of the Leo Trio fit easily in the same eyepiece field of view at moderate magnification. Close observation or long-exposure photographs reveal many features, including spiral arms and dark bands of gas and dust. There’s a lot to see and contemplate in the Trio, so check it out if you get the chance.
After you observe these three galaxies, you’ll still have more than two trillion more to explore in the visible universe. Astronomy is truly an avocation with no end point and infinite possibilities.
The Morning Sky
The morning planetary lineup continues this week. The waning crescent moon joins Jupiter, Saturn, Uranus, Neptune and Pluto as we enter the weekend. Jupiter is very bright and getting bigger and brighter by the day. Dim Pluto remains invisible to all but the largest amateur telescopes.
The Evening Sky
Venus, Earth’s evil twin, is creeping up the evening sky a little more with each passing day. Spot blazing Venus low in the west after sunset. Mars forms a straight line with the twins of Gemini this week. Look above Venus in the west after dark to find, from left to right, Mars, Castor and Pollux. In the east, the last member of the Summer Triangle asterism is up by about 10 p.m.
Dan Price is a NASA/JPL Solar System Ambassador and informal educator. He leads the Night Sky Tours at Josephine Sculpture Park. Have a question about astronomy or space science? Send an email to firstname.lastname@example.org and it might be featured in a future column.