Jun 26, 2000

Giant Planet Power Breakfast

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June 27, 2000
-- Dawn comes early this time of year in the northern hemisphere, but for early-risers this week there's a breakfast treat to make waking up worthwhile. On Wednesday and Thursday morning, June 28 and 29, the giant planets Jupiter and Saturn will appear just a few degrees from the delicate crescent Moon in the eastern sky before sunrise.

"Jupiter and Saturn have spent much of the last few months hidden in the bright glare of the Sun," says George Lebo, a Marshall Space Flight Center Summer Faculty Fellow from the University of Florida Dept. of Astronomy. "Now they're rising about 2 hours before dawn. For the rest of the year the pair will be easy to see. In August, Jupiter and Saturn rise around midnight. By November the two will be high in the southern sky soon after the Sun goes down."

Above: "Look at that Mooooo'n!" Artist Duane Hilton created this rendition of Jupiter, Saturn and the waning crescent moon in the pre-dawn sky on June 28, 2000.

Jupiter and Saturn are easy to spot because they are so bright. This week Jupiter shines at magnitude -2.1 while Saturn is about 6 times dimmer at magnitude +0.3. Simply look due east between 4:30 and 5:00 a.m. local time. The pair of bright planets will appear 20 degrees above the eastern horizon.

As an added bonus this Wednesday and Thursday morning (June 28 and 29, 2000), a slender waning crescent Moon will appear to pass less than ten degrees from Jupiter and Saturn. Although the trio will appear to be close together in the sky, they are in fact very far apart. The Moon is only 368 thousand km from Earth, while Jupiter and Saturn are 863 and 1480 million km away, respectively.


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Jupiter, Saturn and the crescent Moon are so bright that they can even be spotted from urban areas where light pollution normally makes stargazing difficult. Dark-sky observers can enjoy an extra treat: cradled in the arms of the slim crescent Moon will appear the ghostly outline of the full Moon, a dim glow that astronomers call "Earthshine."

Like all the planets we see in the night sky, including Jupiter and Saturn, the Moon does not shine by its own light. It reflects sunlight. The side of the Moon facing the Sun shines brightly; the side facing away is nearly dark. The only significant illumination on the "dark side of the Moon" is due to Earthshine -- sunlight that bounces off the Earth and falls on the lunar surface. A slender crescent Moon with Earthshine is widely regarded as one of the most delicate and beautiful sights in the night sky.

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"The phase of the Earth as seen from the Moon is nearly full when the Moon is crescent," explains Lebo. "Because the Earth is four times bigger than the Moon and is a ten times better reflector, the 'Full Earth' is 160 times brighter than the 'Full Moon.' That's why earthshine is so noticeable."

Left: The eastern pre-dawn sky on June 28, 2000, as seen from mid-latitudes in the northern hemisphere. Saturn and Jupiter appear approximately 20 degrees above the horizon in the constellation Taurus. Observers will note a reddish-orange 1st magnitude star not far below Jupiter. That's Aldebaran, the fiery eye of Taurus the Bull. The beautiful Pleiades are also near the pair of bright planets. (Southern hemisphere observers can also see the planets before dawn, but for them this sky chart should be rotated approximately 90 degrees counterclockwise.)Web LinksThe closest meeting of the two largest planets in 20 years!" - Jack Stargazer, Episode #00-26

This Week's Sky at a Glance -from Sky & Telescope