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Star Watch

Saturn temporarily crosses paths with Virgo and the crow

By Alan M. MacRobert
Globe Correspondent / April 2, 2011

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April finds the planet Saturn climbing the southeastern sky. Saturn shines low as twilight fades, but by 9 p.m. it is higher, in excellent view, glowing with a pale yellowish light.

Helping to identify Saturn is the twinkly star Spica below it, by about a fist-width at arm’s length. Closer above Saturn and a bit to the right is fainter Porrima. High above them is Denebola, as shown here.

Most of us live where the stars are partly hidden by light pollution, the skyglow from all the badly designed and improperly aimed outdoor light fixtures that waste some of their light sideways and upward. Even so, if you look to the right of Spica, you can probably find the four dimmer stars that form the distinctive springtime pattern of Corvus, the crow.

If you live under a sky where you can see as many faint stars as the ancients did, you can connect further dots to make a more realistic crow. He’s eyeing Spica as if to steal it. Spica, in turn, is the brightest star of the big constellation Virgo, a girl holding Spica in her hand. Its name means “ear of wheat.’’ In some versions of the mythology, Virgo is sowing seeds onto springtime fields, and again, you can connect dim dots to create an expressive stick figure doing just that.

Saturn is just a temporary intruder in Virgo’s foreground. Two years from now it will cross into Libra, the next constellation east along the zodiac, below Virgo’s feet.

The end of all sightHow far is Saturn? It’s only 74 light-minutes from Earth. The light you see from it after dinner left it when you were heating the oven.

Spica, on the other hand, is 260 light-years distant. The light you see from it after dinner left it when Benjamin Franklin was starting to tinker with electricity.

How much deeper into space and time can you see when you look in this direction? A pair of binoculars reveals many fainter stars. Some of these are several thousand light-years distant.

A good amateur telescope can show (if you have precise charts) galaxies in the great Virgo Galaxy Cluster, which is centered in front of Virgo’s face and outstretched arm. Most of these galaxies are 40 to 70 million light-years away. Their light has been in flight toward us since the early Age of Mammals and the last of the dinosaurs.

Just in front of Virgo’s neck is the sky’s brightest quasar, 3C 273. Amateur astronomers know it as a barely detectable speck in an 8-inch telescope. Its light dates from 2.4 billion years ago, when Earth was half its present age and bacteria were the most advanced life forms.

Large observatory telescopes routinely see back 5 billion years and more, older than the Earth, sun, and solar system.

The farthest thing that can ever be seen is the weak cosmic microwave background, which wallpapers the whole sky as seen by radio telescopes. It dates from just 380,000 years after the Big Bang, which happened, by the best current accounting, 13.75 billion years ago, plus or minus 0.8 percent.

Beyond that we cannot see. Light from farther away literally has not had time to get here. And the way space is expanding, it never will.

But there’s surely more beyond, lots more. The leading theory that explains how and why the Big Bang happened and what came before predicts that our visible universe is smaller, compared with the wider spaces beyond, than a grain of sand is compared with our visible universe.

And then some.

There’s good evidence that this theory, called the “inflationary universe’’ model, is truly the way things happened. It also predicts that the vast spaces beyond our 13.7-billion-year “horizon’’ contain basically the same things as what we see closer by: stars, galaxies, and the rest. In fact, if you take the inflation model at face value, it predicts that the wider universe is infinite, in which case, numbers and size comparisons do not apply at all.

But physicists and philosophers have no idea whether an actual, physical infinity of any kind is possible. As best we can tell, every aspect of reality is built in such a way that numbers can apply. And that’s really all that anyone can say about this farthest frontier. For now.

Easy-to-use maps of stars and constellations across the entire evening sky are available at SkyandTelescope.com/ gettingstarted. Alan M. MacRobert is a senior editor of Sky & Telescope magazine in Cambridge (SkyandTelescope.com). His Star Watch column appears the first Saturday of every month.

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