M86 and Galaxies

Spring is galaxy season. The Milky Way winds low around the horizon leaving the thin part of the galaxy overhead making the best time to look up and out through our galaxy to other galaxies millions of light years away. The larger galaxies in this image range from 15 million to 40 million light years away. Our galaxy is estimated to be between 150,000 to 200,000 light-years in diameter making these galaxies well beyond the stars and objects inside the neighborhood of our Milky Way.

The two brightest, fuzzy objects in the right center of the screen are the elliptical galaxies M86 and M84. The two galaxies in the upper left are known as “The Eyes.”

Speaking of eyes, in 1823 Wilhelm Olbers used his to look up at night and wondered why it is dark at all.

This time of year we expect the night sky to be darker without the Milky Way overhead and fewer stars to see. But Olbers wondered. If the universe were infinite and stars in the universe are distributed uniformly, he figured the night sky should be all light. Stars get dimmer the further they are away but the number of stars we see looking out through a given wedge of space increases with distance. It turns out, in one of those easy but elegant mathematical ways, the number of stars increases with distance in exactly the inverse ratio at which the intensity of starlight diminishes. The two effects, thought Olbers, should only cancel each other out. Stars get dimmer the further out you look, but there are equally more of them and every where we look we should see light.

But it is clearly not so in early April. The sky overhead is relatively devoid of stars and it takes a telescope to bring out more images. But even the image above, taken through my telescope, has plenty of dark space.

Why is the night dark?

-Mark Bailey, Torrey, Utah, April 20, 2021