Have A wonderful Weekend

Have A wonderful Weekend
Have A wonderful Weekend)))As even casual stargazers know, some stars are brighter than others. Many are so faint they are barely detectable while some are so bright they can be seen from light-polluted cities. One star in particular--our Sun--is blindingly bright. To make sense of these variations, astronomers use a measurement scale called visual magnitudes. It's a reverse scale where the brighter the object, the lower the magnitude number. In 120 BCE, long before the invention of the telescope, the Greek astronomer Hipparchus devised the first scale by which he ranked stars into six levels of brightness. (Our Sun wasn't recognized as a star then.) The brightest stars he considered "first magnitude." Those barely visible were "sixth magnitude." The rest were equally ranked in between. Although imprecise and cumbersome, his scale has been used ever since. Modern astronomers have made the scale more precise, and have expanded it to measure the full range of brightnesses, from our Sun to objects fainter than the Greeks could imagine. The scale includes fractions to account for subtle differences in brightness. For example, a star's visual magnitude might be +3.6. The scale also now dips into negative numbers for very bright objects and goes well beyond +6 for objects fainter than the naked eye can see. The difference in brightness between magnitude values is two and one-half times. For example, Virgo's Spica with a magnitude of +1 is two and one-half times brighter than Polaris (the North Star) with a magnitude of +2. The apparent brightness of stars -- how bright they appear from Earth -- depends primarily upon two factors: luminosity (their absolute brightness, i.e., the actual amount of light they give off) and distance. Our Sun, a star of average brightness, appears so bright because of its nearness. Its visual magnitude is measured at -27. By contrast, Orion's supergiant Rigel is 50,000 times brighter than our sun, but at a distance of 900 light years, its visual magnitude is 0. Even at that distance it is still the 7th brightest star in our night sky. Viewed from Rigel's distance, our Sun wouldn't even be visible to the naked eye. Polaris, the North Star, at 650 light years away, is magnitude +2. Venus, which only reflects sunlight but is much nearer than the stars, appears much brighter with a magnitude of -4. From urban areas where light pollution is a problem, the naked eye can only see objects down to 3rd magnitude or so whereas from rural areas, objects of 5th and even 6th magnitude can be seen. Thus, naked-eye urban stargazers see a few as dozens, and at most a few hundred, stars, whereas the rural stargazer can see upwards of a couple of thousand. Typical 7X50 binoculars can reveal objects down to about 8th magnitude, and even fainter under excellent viewing conditions. The Hubble Space Telescope has taken photos of incredibly faint objects at magnitude +30, which, it has been said, is comparable to seeing a candle flame several thousand miles away.
creado por: angelll2

Califica esta imagen:

  • Actualmente 5.0/5 estrellas.
  • 1
  • 2
  • 3
  • 4
  • 5

13 Votos.

Compartir este Blingee

  • Facebook Facebook
  • Myspace Myspace
  • Twitter Twitter
  • Tumblr Tumblr
  • Pinterest Pinterest
  • Compartir este Blingee más...

Enlace de acceso directo a esta página:



Sellos de Blingee utilizados

Se han usado 9 gráficos para crear esta foto "have a wonderful weekend".
White Glitter
Kerstie: Yellow Birds
Fantasy bird birds spring summer
amon // house
Simple White Pattern

¿Deseas hacer un comentario?

Únete a Blingee (para una cuenta gratis),
Iniciar sesión (si ya eres miembro).

Nuestros socios:
FxGuru: Special Effects for Mobile Video