M3: A bright globular cluster in the spring sky
In last month’s column, I wrote about galaxy season, which always comes on in the spring of the year. This is the time when many far away galaxies can be seen, lying near the constellation Leo and its surrounds.
Galaxies are wonderful to see and a good challenge for astrophotography. However, I also want to tell you about one of the brightest globular clusters in the spring sky, M3.
A globular cluster is a collection of stars lying in the halo of the Milky Way, just outside the actual borders of the Milky Way. Astronomers believe globular clusters are made of material left over from galaxy formation that wasn’t quite drawn into the main mass of the host galaxy. When I say “a collection of stars” I mean a kind of structure that can contain upwards of a million stars, gravitationally attracted to one another so as to form a globe or ball of stars rather close together. One of the very best of these clusters is M3, discovered by Charles Messier in 1764. The stars appeared to be so closely packed in his small refractor telescope that he thought he had found what we call a galaxy now. However, closer inspection, in larger telescopes, revealed about 500,000 stars, closely grouped into the globular shape characteristic of such objects.
M3 has a radius of about 90 light years. So, we have 500,000 stars packed into a globe about 180 light years across. What a sight the sky would be if we could see the sky from a planet circling one of those 500,000 stars near its core! If we were viewing such a sky, I wonder if, as humans, we would ever get any sleep, so bright would be such a sky.
It is thought that M3 is about 11.39 billion years old. Thus, the stars in this cluster would be among some of the oldest stars known. M3 lies about 34 thousand light years away from us, but it is still fairly bright in the night sky and we are seeing it as it was 34,000 years ago. However, it would not have changed much in appearance now.
If you want to find it in April, find the bright, tawny-colored star Arcturus, rising directly in the east, well-placed above the eastern horizon after 10 p.m. Move your binoculars directly up from Arcturus about one fist width or a bit more. Scan the sky up and down and you might find it. It is a very difficult naked eye object, right at the limit of most people’s visual ability. In binoculars, it will appear as a tiny fuzzy ball, but rather brighter than most galaxies would appear in the same binoculars. It will be small and quite compact in the sky. If you can see it in a telescope of 4 inches or more, the individual stars will begin to appear on the edges. As more aperture is trained on this object, the dense core of the cluster will be revealed. If you can increase the telescope’s magnification, higher power will show more stars.
To help you appreciate what this object is like, I have included an image I made of it using a 16inch ‘scope. The stars are revealed all the way to the core. It repays using a search engine to find professional images of this object, made with large telescopes. It is a wonder! There are over 100 of these objects surrounding our galaxy but not in the mass of the Milky Way itself. Professional astronomers, with very large telescopes, have discovered globular clusters in the outer halos of several other galaxies far from our galaxy — globular clusters are apparently common in our universe.
More and more clear nights will occur as we move well into spring and then transition to summer. More and more wonders will be revealed. Put on your bug stuff, dress comfortably and look out into the incredible universe surrounding our little, blue planet.