By Peter Becker
How many stars can your count in the sky? Maybe this seems like a childish notion, but arenít we all ever learning and amazed at the wonder about us? To listen to some, one would think mankind has it in full control and is master of his own destiny with optimistic assurance for tomorrow. Yet on this tiny- minuscule- speck of wonderful dust we call Earth orbiting a fairly average star among billions in the Milky Way, in turn one of practically countless other systems in the Universe as we know it, we at any age have a lot of cause for awe.
With that, how many stars can you count? In the daytime of course thatís easy! You can count one- the Sun.
At night, if the sky is very dark and clear and you have a wide open view, it would seem there are millions of stars spread across the celestial dome above you, in view without optical aid. Actually, the number of stars you can see at any one time is about 7,000.
Star brightness is measured on a scale of magnitude, with the higher the number being the fainter the star. One would think then that a zero magnitude star would be the brightest in the night, but oddly, there are two so bright they are listed with negative (-) magnitudes. Sirius, the brightest in the night sky, is -2.
There are 10 stars brighter than +1st magnitude and 40 brighter than +2. There are 140 brighter than +3. There are 530 more brilliant than +4 and 1,620 brighter than +5. There are 4,850 stars brighter than +6, and 14,300 of greater magnitude than +7.
The unaided human eye normally can see as faint as +6th magnitude, so in the entire Celestial Sphere there are approximately 14,300 stars you can see. Naturally we only see half the Celestial Sphere at any one time, so about 7,000 stars will be above your horizon if it is very flat (as you see on the ocean from a ship). Thereís a planet eclipsing the other 7,000 stars- the Earth! We are in a state of constant TOTAL STELLAR ECLIPSE.
Of course the number of stars you actually do see will likely be much less, given hills, trees, passing clouds, moon light, light pollution from manmade sources, time given to allow your eyes to adjust to the darkness, and oneís eyesight.
Binoculars will deepen your plunge into the vast cosmic ocean and reveal stars to perhaps +9th magnitude. A small telescope, such as a department store refractor with a front "objective" lens of two inch "aperture" (width) will show you stars of +11th magnitude. A six inch telescope show stars fainter than +13th magnitude. A 10 inch telescope almost reaches +14.5.
The number of stars seen increases exponentially with deepening magnitudes as well as telescope aperture. There are 41,000 stars brighter than +8; 117,000 brighter than +9; 324,000 brighter than +10; 870,000 brighter than +11; 2,270,000 brighter than +12; and so on. Stars brighter than +20 number 1 billion!
Last Quarter Moon is on April 3.
Send your notes (and counts!) to email@example.com.
Keep looking up!