Brightness and Colors

Brightness of Celestial Objects

Magnitude ] The magnitude measuring the brightness of a celestial object. In ancient times, the greeks were wont to classify stars into six “values” as their apparent brightness: 1 for the brightest stars, for up to 6 people located at the limit of visual perception (with the naked eye). Over the centuries, it has retained these conventions, but added the magnitude 0 for the brightest stars as magnitude 1, and one negative magnitude expresses the brightness of very bright stars. so the more an object is brighter, its magnitude is small or even negative. When switching a magnitude to the next, the brightness ratio is about 2.5. a magnitude of 4 planet is 2.5 times less bright than magnitude 3 planets.

Apparent Magnitude ] Brightness of a celestial object from earth. For example, -1.6 to sirius, the brightest star in the sky, -26.7 for the sun. that of the full moon is -12.9. For stars visible to the naked eye, it is between -1.5 and 6.5.

Intrinsic or Absolute Magnitude ] Brightness some celestial object would have if it was placed at a distance of 10 parsecs (32.6 light years either) from earth.

Color Celestial Objects

In visual observation (binoculars, telescope) many celestial objects appear less colorful than they really are. This is not due to the telescopes, which usually faithfully recreate the colors of these objects, but the eye is not sensitive enough to their low brightness. So we’ll see these objects only in shades of gray.

However, visual observation one can see the true colors of the brightest objects such as :

Planets with a suitable instrument, the colors of most planets are shown. saturn (yellow), jupiter (blue / green / yellow), mars (red) and venus (white / yellow).
Stars there are even with the naked eye, the colors of the brightest stars.
Double stars: some bright double stars show two stars of different color.
M42, the Orion nebula : It is the only nebula sufficiently large and bright sky to present some colors (blue/green) by visual observation. the green color is perceived more easily because the human eye is more sensitive.

>> The larger the diameter of the telescope is, the more it will capture light and we distinguish colors. Apochromatic glasses, which offer a particularly mixed picture are astronomical instruments that render better the actual colors of celestial objects, including at high magnifications. However, most intrinsically colored celestial objects appear gray, whatever the instrument used. only astrophotography helps overcome this problem. The long exposure time (or the addition of photos) coupled with digital sensors sensitivity much higher than that of the human eye, are used to capture maximum light and so reveal the true colors of observed objects.

Although it may seem disappointing at first,
directly observe such faraway objects provides an emotion can replace a photograph, as beautiful as it is. Some amateur astronomers will also swear by visual observation.