Discussion in 'Nature' started by gwyatt, Aug 21, 2009.

  1. Why when you take a nightscape/starscape you get red stars and blue stars? This might be an astrology question but I thought I would ask here. It has puzzled me the last few nightscape.
  2. Hmh, Hmh: Astronomy , not astrology.
    Red stars are called "late type" by astronomers, they have temperatures of the order of say 3000 to 4500K and therefore glow reddish compared to the sun (which has about 5600K). The blue ones astronomers call "early type" and they can have 10000 to 30000K. The two most easy to spot and famous ones in your picture are alpha and beta Orionis: alpha, in the picture being the are lower left edge of Orion is also named Betelgeuse , is a late one, glowing reddish with about 3500K. Upper right is beta, called Rigel , glowing blueish at about 11000K. Your eyes see them not coloured because the color perception is not sensitive enough.
  3. Erm…that would be astronomy, not astrology, and the answer is simple: stars come in all sorts of colors. It mostly depends on the surface temperature of the star. Our own nearest star has a surface temperature of about 6500 Kelvins. Cooler stars appear redder, and hotter stars appear bluer. (Hint: all that should be very familiar to photographers.)
    It’s mostly a star’s size and mass that determines its temperature, with the bigger, more massive stars being hotter and bluer and the smaller featherweights being cooler and redder. Bigger stars are also generally brighter beacons — Sirius, which features prominently in your picture, is a classic example. However, distance plays an even more dominant role.
    There are a great many other factors that also contribute to stellar colors, but all are overwhelmed by the ones I mentioned when it comes to naked-eye viewing. For example, objects really really really really really far away are redder, as are other objects moving away from us at high speed. (Yes, there’s a big hint in that preceding sentence that should point you to the work of the man for whom the most famous space telescope was named.) Also, trace elements in the outer atmosphere of a star result in a unique and subtle pattern of enhancing and subduing various wavelengths that serves as a fingerprint for each star.
    If I’ve piqued your interest sufficiently, may I strongly suggest either taking an introduction to astronomy course at your local community college and / or spending some quality time at your nearest library?
  4. Hello Thomas and Ben,
    Thank you so much for making this clear to me and taking the time to comment. I think I just might have to take a class... thanks Ben!
    Greg Wyatt
  5. Thomas, looked like you photographed Orion and Taurus the Bull. If you have any binos or a small scope. Look at Orion's belt.
  6. You should also be aware that longer exposures (even with LENR) may generate red and blue dots that you might mistake for stars. These are pixels that have expired during the exposure and appear as red or blue dots. They can usually be identified by the fact that they appear as pin-point dots rather than the short streaks that the stars make due to Earth rotation during the exposure. I have also noticed (with my 5D MkI) that I occasionally get little white "X"s which I assume are caused by the same long exposure amp noise phenomenon.

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