Friday, May 23, 2014

Stars?

I have always enjoyed looking at the stars in the sky.  A fellow posted this interesting article we may not know or may have forgotten about stars.

Every star you see in the night sky is bigger and brighter than our sun. Of the 5,000 or so stars brighter than magnitude 6, only a handful of very faint stars are approximately the same size and brightness of our sun and the rest are all bigger and brighter. Of the 500 or so that are brighter than 4th magnitude (which includes essentially every star visible to the unaided eye from a urban location), all are intrinsically bigger and brighter than our sun, many by a large percentage. Of the brightest 50 stars visible to the human eye from Earth, the least intrinsically bright is Alpha Centauri, which is still more than 1.5 times more luminous than our sun, and cannot be easily seen from most of the Northern Hemisphere.

You can’t see millions of stars on a dark night. Despite what you may hear in TV commercials, poems and songs, you cannot see a million stars … anywhere. There simply are not enough close enough and bright enough. On a really exceptional night, with no Moon and far from any source of lights, a person with very good eyesight may be able to see 2000-2500 stars at any one time. (Counting even this small number still would be difficult.). So the next time you hear someone claim to have seen a million stars in the sky, just appreciate it as artistic license or exuberant exaggeration – because it isn’t true!

Red hot and cool ice blue – NOT! We are accustomed to referring to things that are red as hot and those that are blue as cool. This is not entirely unreasonable, since a red, glowing fireplace poker is hot and ice, especially in glaciers and polar regions, can have a bluish cast. But we say that only because our everyday experience is limited. In fact, heated objects change color as their temperature changes, and red represents the lowest temperature at which a heated object can glow in visible light. As it gets hotter, the color changes to white and ultimately to blue. So the red stars you see in the sky are the “coolest” (least hot), and the blue stars are the hottest!

Stars are black bodies. A black body is an object that absorbs 100 percent of all electromagnetic radiation (that is, light, radio waves and so on) that falls on it. A common image here is that of a brick oven with the interior painted black and the only opening a small window. All light that shines through the window is absorbed by the interior of the oven and none is reflected outside the oven. It is a perfect absorber. As it turns out, this definition of being perfect absorbers suits stars very well! However, this just says that a blackbody absorbs all the radiant energy that hits it, but does not forbid it from re-emitting the energy. In the case of a star, it absorbs all radiation that falls on it, but it also radiates back into space much more than it absorbs. Thus a star is a black body that glows with great brilliance! (An even more perfect black body is a black hole, but of course, it appears truly black, and radiates no light.)

There are no green stars. Although there are scattered claims for stars that appear green, including Beta Librae (Zuben Eschamali), most observers do not see green in any stars except as an optical effect from their telescopes, or else an idiosyncratic quirk of personal vision and contrast. Stars emit a spectrum (“rainbow”) of colors, including green, but the human eye-brain connection mixes the colors together in a manner that rarely if ever comes out green. One color can dominate the radiation, but within the range of wavelengths and intensities found in stars, greens get mixed with other colors, and the star appears white. For stars, the general colors are, from lower to higher temperatures, red, orange, yellow, white and blue. So as far as the human eye can tell, there are no green stars.

Our sun is a green star. That being said, the sun is a “green” star, or more specifically, a green-blue star, whose peak wavelength lies clearly in the transition area on the spectrum between blue and green.  This is not just an idle fact, but is important because the temperature of a star is related to the color of its most predominate wavelength of emission. (Whew!) In the sun’s case, the surface temperature is about 5,800 K, or 500 nanometers, a green-blue. However, as indicated above, when the human eye factors in the other colors around it, the sun’s apparent color comes out a white or even a yellowish white.

Our sun is a dwarf star. We are accustomed to think of the sun as a “normal” star, and in many respects, it is. But did you know that it is a “dwarf” star? You may have heard of a “white dwarf,” but that is not a regular star at all, but the corpse of a dead star. Technically, as far as “normal” stars go (that is, astronomical objects that produce their own energy through sustained and stable hydrogen fusion), there are only “dwarfs,” “giants” and “supergiants.” The giants and supergiants represent the terminal (old age) stages of stars, but the vast majority of stars, those in the long, mature stage of evolution (Main Sequence) are all called “dwarfs.” There is quite a bit of range in size here, but they are all much smaller than the giants and supergiants. So technically, the sun is a dwarf star, sometimes called “Yellow Dwarf” in contradiction to the entry above!

The Universe can make me feel pretty insignificant but I've learned that God loves the speck!

Twinkle twinkle, little star, did you know that stars don't twinkle?

Ed

7 comments:

  1. The great thing with stars is that spending just a few nights with a pair of binoculars and a star guide will teach you the names of most constellations for life. I mean, there's a cute tiny weeny constellation called the Dolphin visible most of every clear nights, which kid would not remember that for life without a single memory effort. And you make the sky your own too. For instance, there is certainly no Eiffel Tower constellation in the sky, but which kid living 20 miles from Paris would call the third smallest constellation the Arrow constellation? You quickly learn the names of the brightest stars too, or how to find them, starting with the North Star. It would be better for English speakers to use English names for constellations though. I mean, Plowman is easier to remember or relate to than Boötes... ;)

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  2. By the way, meteor shower tonight: http://www.escapistmagazine.com/news/view/134749-Be-the-First-Humans-to-Watch-Tonights-New-Meteor-Shower

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  3. 2 AM, I would love to but I am normally sawing logs at that hour, serious logs. If LuAnn didn't need to be somewhere early tomorrow, we both would.

    We even have a fire going on the patio.

    Ed

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  4. Ed, Chimel or others , I just can't get my head around there not being some wall at the end of the universe or something. Any thoughts on how it can just go on and on?Completely boogles the mind--kevin in Ontario

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    Replies
    1. A "wall?" You mean that thing that's 99.999999% air, with a few tiny particles in between? How is that putting a limit to the end of the universe when it is so immaterial that it can so easily be gone through? Heck, there are neutrinos and what not particles emitted at the Big Bang that are going through the whole Earth without even noticing or slowing down.

      I am more worried about the constant "wall" of clouds in Seattle that prevents anybody from ever experiencing meteor showers...

      But yeah, there are many things that boggle the mind with the Universe, like its size or infinity, but also its constantly growing acceleration rate: In a few hundred thousand years, stars and galaxies will have grown so far apart that there would be very few left in the sky for us to observe. Several scientists are saying that it would have been very difficult for astronomy to develop if we were not living in this specific time where observations are still possible. There's also the unknown about the expansion of the universe, will it continue growing forever, or will some gravity force eventually pull it back to its center, maybe to restart a new Big Bang like a pulsation? What about the string theory that shows there are at least 10 dimensions, and possibly parallel universes? At the pace science progresses, I am sure we'll have the answers some day, but probably not in my lifetime, and that shouldn't prevent anyone from finding good sleep.

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  5. Kevin, I've let my mind explore the Universe and it could literally implode the human mind. The Big Bang Theory gang might be able to explain it but I know I can't!

    https://www.google.com/#q=how+big+is+the+universe

    Ed

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