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Brightness Starlight is equal to 51 Sirius' or 4 Venus' (at maximum) The brightest planet is Venus at a magnitude of -4.5 and the dimmest is Pluto whose brightness varies from 13 to 14 magnitude. Mars has the greatest range of brightness. It can range from +1.6 magnitude to -3.0 (see Synodic period). At its brightness Mars can outshine Jupiter, as it did in September 1988. September 1988 is the time when I got interested in observational astronomy, when I saw this mysterious bright orange dot in the sky. Combined with Jupiter, the night sky came alive! If you were to draw a bird's eye view of both Earth and Mar's orbit, you would find that at one end Mars is nearly twice as close than at the other end. Every 15 or 17 years, Mars is twice as close at a favorable opposite than at an unfavorable one. And in 2003, this favorable opposition is the most favorable of the last 1000 years. Albedo is a percentage of the light that is reflected off an object. With an albedo of 1, all light is reflected, with an albedo of 0, all light is absorbed. Venus has the highest albedo of the planets, 0.65, which helps make it the brightest planet. If Venus had an albedo similar to Jupiter, they would be about the same brightness. Enceladus, a moon of Saturn, has an albedo of 0.99, since it is made mostly of ice. Mercury has the lowest albedo of the planets at 0.1 and some asteroids approach 0.01. At 0.01 albedo, an object is like the blackest coal you can imagine. |