Sunday, January 29, 2012
When were the stars born?
John Goss
John Goss is chairman of the Mid-East Region of the Astronomical League and a former president of the Roanoke Valley Astronomical Society.
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- Look far beyond the stars of the Milky Way
Blog
Undoubtedly, the stars you see are ancient, every one of them. Sure, a few new ones are born every year, but none of those can be seen with the unaided eye. Of all the stars visible in our winter sky, which are the oldest and which are the youngest?
It is hard to fathom how old the stars really are. One way of trying to comprehend their immense life spans is by constructing a timeline, say one with an inch equaling 100 years, about the length of a long human lifetime.
On this scale, the first 8 feet of the timeline contains all human events since civilization began 10,000 years ago. Over half a football field farther, the first Homo sapiens appear.
A popular binocular highlight in winter skies is the Orion Nebula, appearing as a fuzzy area below the Hunter's belt. This is a star-forming factory where several nascent stars, which are far too dim to see without a telescope, recently emerged from their cocoon of gas and dust. How recently? About 300,000 years ago, or nearly the length of a football field on our timeline.
To reach the point marking the birth of the youngest star seen by the unaided eye, two-thirds of a mile must be covered. All along this stretch shines the strange sounding Zeta Puppis. This star, which appears as bright as those in the Big Dipper, is not easily found because it never rises high above February's southern horizon.
Another young star is also one of the brightest in our winter sky.
At less than 8 million years old, Orion's Rigel shines a little more than a mile along the timeline. To Rigel's lower left lies the constellation Canis Major, which contains two more very young stars somewhat older than Rigel. Eta and Delta Canis Majoris both formed about 10 million years ago, putting their beginnings well over a mile down the line.
The great majority of stars first appear between 10 miles and 50 miles down the line, quite a ways from the point marking the start of civilization. The creations of the very old stars lie much farther still.
Eta Cassiopeiae, the third oldest star visible, was born 4.5 billion years ago. It's been shining since its formation about 710 miles down the timeline.
The second oldest star visible may come as a surprise, even to seasoned skywatchers. Unlike all the others in the sky, it is found only in the daytime.
Our 5-billion-year-old parent star, the sun, began shining 800 miles down that line, or the distance from Roanoke to New Orleans. The planets, including our Earth, were formed about 400 million years after the sun appeared, placing their beginnings 75 miles closer than the Crescent City. Isn't it odd that our Earth is much older than all the visible stars but two?
(At 7:30 p.m. Feb. 9 look through binoculars at ancient Venus brilliantly glowing in the west for a surprise. The faint companion immediately to its left is not an ancient star, but the ancient planet Uranus.)
Only one star visible is older than the sun, but not by much.
Twinkling unassumingly about 950 miles along the timeline is the 6-billion-year-old Tau Ceti, a favorite story setting for science fiction tales. This star currently appears in the southwest a couple of hours after sunset and can be found from a dark location using the proper star map.
Keep in mind that these ages and these distances refer only to the visible stars. Incredibly, most stars in the universe are much older, but they can't be seen with the unaided eye.
How do these stellar ages and distances compare with the age of the universe? Try traveling 13.7 billion years to the timeline's beginning at over 2,100 miles!
