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The Big Dipper
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One of the most easily found constellations in the northern skies is Ursa Major - the Big Bear. It’s so easy to find because inside Ursa Major is the well-known Big Dipper.
There are seven stars that make up the Dipper. (There are helpful star
maps for this whole article at http://firstlightastro.com/icolumn.html.)
With the exception of the stars on both ends, the Dipper is an “association,”
astrospeak for a group of stars which were born at about the same time
out of the same cloud and are also traveling in the same general direction.
The stars on the Dipper’s end are not going with this flow; they
are actually tens of trillions of miles farther away and moving in different
directions. Because of the roaming about of all these stars the Dipper
won’t look like a Dipper in 100,000 years. By then, if you’re
around, it may be called The Big Tire Tread on the Side of the Freeway.
The
stars that make up the leading edge of the “scooper” part of
the Dipper are Merak and Dubhe. These are the Pointer Stars that most
kids learn about in grade school pointing the way to Polaris, the North
Star.
Dubhe, the more northern of the Pointer Sisters, has a secret. It’s
a massive old star 60 times bigger than our sun, but a closer binocular
look will reveal a tiny bluish companion star. These two are revolving
around each other taking a mere 600,000 years to complete one revolution.
But wait, there’s more to Dubhe and its buddy than meets the eye!
As astronomers studied the light from these two, it came to light that
both of them had tinier - and very close - companions of their own. Thus,
what appears as Dubhe, the star at the pour spout of the Dipper, is really
a four-star system.
But Dubhe and friends are hardly the only stars out there with mates.
The second star from the end of the handle of the Dipper is a star system
that is out of this world. Peering closely at them you may see a bright
star named Mizar and a dimmer one called Alcor. Spotting that dim one
was an eye test used by several peoples including the Romans and some
native American tribes. But the fun is just beginning...
Grab some good binoculars and you’ll see a second star right next
to Mizar. This is Mizar’s binary buddy, affectionately christened
Mizar B. The stellar friendship between Mizar A and B was first discovered
in 1650 by Italian astronomer Giovanni Battista Riccioli. It was the first
discovery of literally tens of thousands involving stars with companions.
It turns out our bachelor star, the sun, is in the minority.
This couldn’t be better for us.
If you need a planet that can support life order up one bachelor star
exactly like the sun. Those stars with companions can’t hold onto
a planet with a stable orbit. So as intriguing as they are, multiple-star
systems are best seen at a distance - a great big distance.
One more thing about Mizar. Not only are Mizar A and Mizar B going around
each other but it appears that Alcor itself is revolving around the Mizars!
Want more? Each of those stars has another unseen star orbiting them!
Why, Mizar and Alcor are hosting a six-star square dance!
Until next time, clear skies!
Posted by Administrator at 2000.05.14 09:36 AM | Comments (0)
