First rule of stargazing is important one


By Tom Burns - Stargazing



The first rule of stargazing is to remember where you are. From a dark, rural observing location in June, you’ll discover that you’re standing on a speck of rock orbiting a below-average star near the edge of a disk-shaped, flattened spiral of stars, gas, and dust called the Milky Way.

Look east at 3 a.m. for the constellation Cygnus, “the Swan,” and you’re looking along the disc into the uncountable stars of one of the spiral arms.

By 4 a.m., when the constellation Sagittarius rises in the southeast, you are staring into the center of the disk. Binoculars reveal far fewer stars than you might expect. A thin but pervasive veil of dust and gas lies between you and the galactic center 40,000 light-years away. (One light-year is about 6 trillion miles.)

In those directions, your Milky Way neighborhood blocks the view of the wider universe.

The experience of the Milky Way under the dark, rural sky in southern Ohio is unforgettable. However, it’s worth a second trip south to get an even wider view of the cosmos.

Just after evening twilight, the meager stars of the constellation Virgo sit high in the south. Virgo is shaped a bit like a tilted Y or cockeyed wine glass.

You are now staring up and away from the Milky Way’s disk. Without the veil of stars and dust to block the view, you can see more-distant locales.

Nestled in the bowl of Virgo’s wine glass and overflowing it into the constellation Coma Berenices are the myriad galaxies of the Virgo Cluster of galaxies. Even in a large telescope, they don’t look like much more than fuzzy patches, but hundreds of them are visible in a telescope and a few that are even accessible by decent binoculars under dark, rural skies.

Don’t let the fact that you are looking at a bunch of “faint fuzzies” deter you. They are, after all, exceedingly far away. Spica, Virgo’s brightest star, is in our own Milky Way galaxy at a modest 40 light-years away. The Virgo galaxy cluster is 54 or so million light-years distant.

I will never forget the fine spring night that I first saw the Coma-Virgo cluster in all its glory. I made the trip to the Big Brothers/Big Sisters camp with two seasoned observers, John Kerns and Dick Suiter. We traveled with my newly built, large telescope, which sat nestled in pieces in the back of my old VW microbus.

The trip south was not without incident. My Vee-Dub had a tendency toward vapor lock, and it stalled on an uphill grade on the way. The parking brake didn’t work very well, so John and Dick had to hold the bus from rolling down while I found rocks to put behind the tires.

After a long wait for the Vee Dub to unlock itself, we finally made it to the camp. The telescope, which stood just a bit taller than me, took about 45 minutes to assemble.

But as evening twilight turned to darkness, John pushed the telescope toward Virgo. “I want to show you something,” he said mildly but with an evil grin.

John them proceeded to show me scores of galaxies in the Virgo Cluster. He navigated chains of galaxies purely from memory. As he did, he rattled off characteristics of each galaxy — size in light-years, distance from the center of the cluster, galactic classification. Here, I thought, is what I want to be and what I want to do for the rest of my life.

By morning twilight, we had observed 150 galaxies. I came to understand that the essential building blocks of the universe are not stars or even galaxies of stars. Clusters of galaxies rule the cosmos. The Milky Way is in a clump called the Local Group that barely makes the cluster cut. The Milky Way and two other multibillion-star galaxies are its main members.

Include its scattering of tiny “dwarf” galaxies of a pathetic few hundred million stars each, and the whole Local Group might stretch to three dozen galaxies.

The 1,500 or so galaxies of the Virgo Cluster make it a rather large galactic by our Local Group standards. That night, we observed only one-tenth of its enormity.

Even some of the individual galaxies of the Virgo Cluster are behemoths.

Of the thousands of such “island universes” available to amateur telescopes, none sets the standard for sheer size better than M87, the centerpiece of the Virgo Cluster.

The jewel in Virgo’s crown looks like a dim, ovoid lump of light. At a distance of 55 million light-years, enormousness fades to faint fuzziness.

How big is big when even the smallest galaxy is mind-meltingly large? Our rather average Milky Way has 200 billion to 300 billion stars. M87 easily tops a trillion.

Our galaxy has at its center an inescapable artifact of its formation — a gigantic black hole. It has a mass of 3.6 million of our suns squeezed down to such density that even light cannot escape its gravitational ferocity.

M87’s black hole weighs in at 3 billion solar masses. Counting everything — central black hole, stars, and every stray molecule of dust and gas — M87 has enough material to make 2.7 trillion suns.

Our Milky Way is no pipsqueak at 100,000 light-years wide. M87 is 980,000 light-years in diameter.

The Milky Way is a normal flattened spiral, like two plates put together at their rims. M87 looks more like an egg. Its stars are spread out much more evenly into a much larger volume of space.

How did M87 get its enormous size and ovoid shape?

Nobody knows for sure, but a good bet is that M87 got its start as an average-size spiral. Back in the early days of the universe, galaxies were much closer together than they are now.

As the galaxies moved around, they often passed near or through each other. M87 may have stripped a considerable amount of material from smaller galaxies as they passed by or through. Sometimes it swallowed weaker galaxies whole.

Those mergers squeezed the galaxies’ gas clouds together, sparking magnificent bursts of star formation. A flurry of early star births helps to account for M87’s large number of stars. It also explains why M87 is now practically bereft of star-forming clouds of dust and gas.

M87 might be the big, bright bully on the galactic block, but its days are numbered.

Because our Milky Way suffered through far fewer galactic interactions, it formed far fewer stars and still has loads of gas to form new ones.

Long after M87 begins to fade, our comparatively wimpy Milky Way will still be making stars and lighting up the cosmos.

For now, the M87 and the Virgo Cluster represent a tiny slice of the true order of nature.

Its galaxies are considered clumped together by universal standards, but they are still separated from each other by millions of light-years. On that wondrous spring night so long ago, I experienced a taste of the true texture of the natural world on its largest scale.

I will never forget it. I will also never forget the debt of gratitude I owe to the two astronerds who led me through the cosmic maze.

Quite naturally, we tiny humans recoil from such vastness and emptiness. Your cluster of galaxies, the Local Group, is a baby compared with its enormous sibling, the Virgo cluster. Compared with such urban accumulations, you live in a tiny backwater of the universe.

The structure of a leaf or the call of a bird seems far more beautiful and far less daunting. But consider this, fellow naturalists: A galaxy consists of all its parts, large and small.

The Milky Way is mostly composed of 300 billion stars. However, our galaxy is also made up of our wondrous planet, every leaf on every tree, and you.

Stunningly, the Milky Way and the Virgo cluster are part of an even larger accumulation called the Virgo Supercluster, which consists of over 100 galactic clusters. Our own Local Group lies at the fringes of the Virgo Supercluster. When you go out and gaze at some of its galaxies, you become the part of the Virgo Supercluster that is looking at itself. You become the eye, the mind, and the heart of 47,000 galaxies spread out over a volume of 110 million light-years.

That’s where the first rule of stargazing takes you.

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By Tom Burns

Stargazing

Tom Burns is the former director of the Perkins Observatory in Delaware.

Tom Burns is the former director of the Perkins Observatory in Delaware.