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Jimmy Westlake: Look into infinity and beyond

On April and May evenings, the band of the Milky Way surrounds us in a ring along the horizon. At that time, we are able to peer out of the top of our home galaxy and into the infinity of deep space. What mysteries await us there?

— In space, there is no up or down, no top or bottom. On Earth, gravity defines our "down" as toward the center of the Earth and our "up" as the direction opposite that, but these have no meaning once you are away from the Earth's influence.

So, when considering our pancake-shaped Milky Way galaxy, the terms "top" and "bottom" are completely arbitrary. If we choose the "top" of our galaxy to be the side toward which the Earth's north pole happens to point, then spring is the time of year when we are able to look right up out of the "top" of the Milky Way and into the depths of intergalactic space. At about midnight in mid-April, or 10 p.m. in mid-May, the hazy band of the Milky Way temporarily encircles us along the horizon such that when we lay on our backs and stare straight up, we are gazing into infinity.

What's out there in that deep, dark ocean? If you could hitch your rocket to a beam of light and travel at light speed straight up out of the top of our galaxy, you wouldn't notice much of a change at all for about 50 years or so, except for the once-brilliant sun receding into the distance and fading from view. In fact, you wouldn't notice too much of a change for the first 1,000 years, as nameless stars stream past your windows. But after a millennium or so, you would leave the crowded disk of the Milky Way behind and enter the sparsely populated halo region of our galaxy. As the millennia tick by, you might see an occasional globular star cluster sail past your window, but after 100,000 years of traveling, there aren't even any more star clusters to break the darkness.

Looking ahead, you might be able to see dozens of faint, fuzzy smudges of light, far in the distance, like so many dandelion floats. These are the galaxies of the Virgo Cluster, so named because from Earth we see them glowing behind the stars of the Virgo constellation. Traveling on your beam of light, it still would take you 60 million years to reach the Virgo Cluster. More than 1,000 galaxies of every shape and size would be visible out of your window: giant elliptical galaxies and majestic spirals like our own Milky Way. After 10 million years of enjoying your passage through the Virgo Cluster at light speed, you would spot only an occasional galaxy passing by your window.

About 320 million years after leaving Earth, you would arrive at the Coma Cluster, a rich galaxy cluster containing thousands of individual galaxies. Once you've traversed this enormous swarm of galaxies, you would enter uncharted regions of the universe, on your way to infinity. Many of the brightest galaxies of the Virgo and Coma clusters can be glimpsed with ordinary binoculars or a small telescope this month as you lay on your back and gaze upward out of the top of the Milky Way Galaxy and into infinity.

Jimmy Westlake teaches astronomy and physics at Colorado Mountain College's Alpine Campus. Check out Westlake's astrophotography website at http://www.jwestlake.com.