Ah, the night sky! Millions of stars!
There are actually far more than mere “millions” of stars over your head, but how many can you see with eyes alone? How about, roughly 2,000 at any one time?
From a dark, rural location, with wide open horizons, approximately couple thousand stars are visible on any clear, moonless night.
That considers a magnitude limit of +6.5, which is as faint as most of us can ever see without the aid of binoculars or a telescope. The magnitude limit is usually a lot higher, given light pollution. You can typically reach down to +4 or +5 magnitude in a semi-rural area.
This also of course assumes your eyesight is reasonably good and you have allowed your eyes to adapt to the darkness after leaving a lit home.
How about from a shopping mall parking lot? Don’t ask!
For some idea of magnitude, the stars of the Big Dipper are magnitude +2 and +3. One might think the brightest star is magnitude 0 but it’s not. Sirius, the brightest star of the night and visible in the southern sky on mid-winter evenings, is (minus) -1.4.
Each magnitude is 2.5 times as bright as the one below it.
The entire sky offers 9,096 stars, down to magnitude +6.5. So where’s the rest?
Under your feet!
One of the planets orbiting a Milky Way Galaxy star is hiding the rest of them. That planet is the Earth, the one you and I ride!
As the Earth spins west to east, the sky seems to spin east to west. So that lovely star, the Sun comes up each day, and thousands of other stars rise as well, visible at night to your eyes alone.
Unless you live (or visit) at the equator, you can never see all 9,096 stars.
The Earth’s axis of spin extends from the North Pole and South Pole at imagined points in the northern and southern sky. Polaris, the North Star, is situated very near the “North Celestial Pole” and is a handy way to measure one’s latitude.
From Hawley, Pa., for example, Polaris is about 41.5 degrees above the northern horizon. All the stars that many degrees from the North Celestial Pole circle around once every 24 hours but keep missing the horizon.
Among the “circumpolar” stars are those of the M-shaped constellation Cassiopeia and the stars of the Big and Little Dippers, which never set as seen from Hawley.
Stars also circle around the South Celestial Pole, and from any given northern latitude, you can never see a host of stars because they never rise!
Folks in Argentina, for example, see the Southern Cross and Dorado the Swordfish, but never see the far northern groups like Cassiopeia and the Dippers.
It is rather fascinating to contemplate that beneath your feet, to other side of the planet Earth, there are constellations of stars.
If there was a hole bored straight down through the center of the Earth to the other side, what would you see?
Next time you are pondering the Earth’s globe, take a look.
From Hawley, Pa. it would NOT be China.
China shares the same northern latitudes as the U.S.A.!
Looking straight down from Hawley, we also would not see the soles of shoes of some Australians, or even the feet of a kangaroo. We’d see the bottom of the Indian Ocean, southwest of Australia.
The full sky - surrounding our planet - is referred to as the “Celestial Sphere.” It took thousands of years for mankind to discern that the stars are not actually fixed points of light on a literal sphere, in which our world was in the center. It appears to be that way, however, just as at first glance our world seems to be flat.
If 9,096 stars doesn’t seem like many, binoculars will allow you see as many as 100,000 stars. A 3 inch telescope brings you about 5 million!
Full Moon is on February 10. From “Down Under,” by the way, the Man in the Moon looks like he’s standing on his head!
A Sky & Telescope article helped inspire this column topic.
Keep looking up!
-- Peter Becker is Managing Editor at The News Eagle in Hawley, PA. Notes are welcome at email@example.com. Please mention in what newspaper or web site you read this column.
Looking Up: Two thousand stars and counting ...
Ah, the night sky! Millions of stars!