by Dave Adalian
How far can the human eye see?
The question sounds like something a Zen master might ask a student to bring him enlightenment, but unlike puzzling over the sound of a single hand clapping, this question actually has an answer.
Two and a half million light years, about 14.7 billion billion miles, is as far as the human eye can look.
That’s how far the empty void between our galaxy, the Milky Way, and our nearest large neighbor, the Great Andromeda Galaxy, stretches, and the Great Andromeda Galaxy is the farthest thing the human eye can see without the help of a telescope.
That distance is also as far back in time as we can look.
To find the Great Andromeda Galaxy find a dark sky away from city lights on a moonless night during late fall or early winter and look almost overhead for the Great Square of Pegasus, a huge square formed by four bright stars. Then look northeast for an M-shaped group of stars in the constellation Cassiopeia and imagine a line between the brightest of these stars and the brightest star in the Great Square. Just east of that line about two-thirds of the way along it in the direction of Pegasus you’ll see the bright glow that is the light of the Great Andromeda Galaxy.
That faint and distant glow left its home galaxy 2.5 million years ago, long before modern human beings walked the Earth. When we look at Andromeda, we are looking back in time and seeing that galaxy not as it is today but as it was in the long ago past.
We’re also seeing almost exactly what a person living on a planet in the Andromeda Galaxy sees he when looks up on a clear and moonless night and gazes back across the empty void and the endless years at the Milky Way, since the two galaxies are very similar in size and form with each containing billions of stars arrayed in vast and sweeping spirals.
If the sky is dark enough and one’s eyes are good enough, the Great Andromeda Galaxy appears huge, stretching about five degrees across the sky or 10 times the width of a full moon.
What isn’t obvious when looking at Andromeda is that it and the Milky Way appear to be on a collision course, moving toward each other at more than 250,000 mph. Not to worry, however. Even at that speed if the two do collide it won’t be for another three billion years.
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The Tulare Astronomical Association and the Tulare County Office of Education will present The Hero, the Lady and the Stars of Early Winter, a planetarium program written and narrated by Starry Nights columnist Dave Adalian Dec. 7 and Jan. 11 with a free star party to follow. For details, check the Starry Nights blog at starry-starry-nights.blogspot.com or the Pena Planetarium website at www.tcoe.k12.ca.us/ImpactCenter/Planetarium.shtm
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This column originally appeared in the Visalia Times-Delta and Tulare Advance-Register on Nov. 22, 2007.
