Sunlight is a precious commodity for life on Earth.
We take it for granted. The Earthís spin is assumed. Without fail, the sun rises every day and sets each night. Thatís a good thing. We watch the lovely sunset and its colors, perhaps wishing the day wasnít so short especially as winter draws near. Yet we have no concern that the sun will rise again and we can sleep content.
Every night we have ample evidence that nothing happened to the sun while we wait for dawn.
The next clear evening this month look nearly overhead for the planet Jupiter. Like a beacon, the Jovian brilliance standing out in dominance over the splendor of stars in the background. Even with the bright stars of reddish Aldebaran to the right, yellow Capella higher up, bright Castor and Pollux to the left, bright Procyon and brilliant Sirius at lower left, and the glory of Orion with brilliant red Betelgeuse and blue-white Rigel rising to the lower right, Jupiter rules.
We call it the King of Planets because it is so huge, the largest in the solar system, yet the only reason we see it all is because of sunlight. Almost like a mirror, the huge expanse of Jupiter, with its lightly shaded cloud deck, reflects back the sun with great intensity.
The sunís reflection reaches your eyes about 54 minutes after the light was emitted from the sun - assuming Jupiter is directly opposite us from the sun. It takes about 31 minutes for sunlight to reach Jupiter; to reflect back to us it takes another 23 minutes. It all depends on the geometry; if Jupiter is far off to the right or left, the sunlight travels longer.
It takes sunlight about eight minutes to reach the Earth. Light moves at a speed of 186,282.4 miles a second. Jupiter, by the way, is on average, 483,682,810 miles from the sun. The Earth is 93 million miles from our star.
Sunlight on Earth is at just the right level for us. It you were to go to Mars, sunlight would be more like daylight on Earth wearing sunglasses. Sunlight at Saturn would match the intensity of an average sunset or sunrise of Earth. At far off Pluto, sunlight would be similar to the light level in your house. To see sunlight as dim as full moonlight on Earth, you would need to travel over 46 billion miles. This is as far as 2003 VB12 Sedna, one of numerous small planetary bodies discovered in recent years far beyond Pluto.
The moon of course gives us the most obvious example of reflected sunlight. When it reaches new moon, however, it isnít shining back at us at all and our night is dark. Last-quarter moon is on Feb. 22 when it is half lit by the sun.
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