astlbtns - Laboratory 4 - Observing the Planets in the...

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26 Laboratory 4 - Observing the Planets in the Night Sky Materials Used: Star and Planet locator, Star Charts, SkyMap © software. Objectives: To investigate the night sky as it will appear this evening and to predict when conditions will be favorable for viewing planets in the future. Discussion: Our solar system consists of the Sun, eight planets and a number of smaller observable objects: comets, meteoroids, etc. All of the planets revolve about the Sun in the same direction and are arrayed a plane, known as the ecliptic plane , except Mercury - whose orbit is inclined about 7 o relative to the ecliptic plane. Since the Sun and planets lie in the same plane they all appear to move across our sky along a common path known as the ecliptic . Determining Visibility Seldom is any celestial object except the sun visible in the daytime sky. Because the sun is very bright (the visual magnitude of the sun is –26.73, the full moon –12.6 and Jupiter –2.9), and because Earth’s atmosphere scatters light from the sun (especially blue light), everything in the daytime sky is washed out by sunlight. Any planet we wish to view in our own solar system from earth must be viewed between sunset and sunrise. On the moon, where there is no atmosphere, stars and planets (including Earth) are easily visible during daytime. Why is this so? To determine when planets are visible in the night sky one must take into account a planet's brilliance. Brilliance or brightness is a function of size, distance, reflectivity and other factors. The more brilliant a planet, the easier it is to see – especially during twilight. The following may be considered a rough guide to how dark the sky must be in order for a planet to be easily visible: Mercury first appears 45 minutes after sunset disappears 45 minutes before sunrise Venus first appears 20 minutes after sunset disappears 20 minutes before sunrise Mars first appears 30 minutes after sunset disappears 30 minutes before sunrise Jupiter first appears 30 minutes after sunset disappears 30 minutes before sunrise Saturn first appears 30 minutes
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astlbtns - Laboratory 4 - Observing the Planets in the...

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