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This month, Venus can guide you to a naked-eye planet that
ancient astronomers inexplicably failed to see.
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April
11, 2006: Ancient people didn't
have TV or electric lights. So, when the sun went down every
night, they got their entertainment by watching the sky. And
it was entertaining. Without city lights to interfere,
the Milky Way was spectacular. Meteors flitted across the
sky. Zodiacal lights chased the sunset.
Of
special interest were the five naked-eye planets, the ones
you could see without a telescope. (The ancients didn't have
telescopes, either.) Countless hours were spent watching Mercury,
Venus, Mars, Jupiter and Saturn, whose movements were thought
to control the affairs of men.
 Would
you believe, in spite of all that watching, they missed one?
There is a sixth planet you can see without a telescope, a
planet named George.
"George"
is not as bright as the others, but it is there, glowing like
an aqua-blue star of 6th magnitude. It measures four times
wider than Earth, has more than 30 moons and a dozen or so
thin rings. George goes around the sun every 84 years, always
spinning on its side as if something knocked it over.
George
is better known as Uranus.
Right:
Voyager 2 took this picture of Uranus in 1986. [More]
English astronomer
William Herschel discovered the planet in 1781 during a telescopic
survey of the zodiac. He promptly named it the Georgium Sidus
(the Georgian Planet) in honor of his patron, King George
III. Later, to the everlasting delight of schoolchildren,
George was re-named Uranus, the Greek god of the sky.
Uranus
had been seen many times before but mistaken for a star. The
earliest recorded sighting was in 1690 when astronomer John
Flamsteed cataloged it as 34 Tauri, the 34th star of Taurus
the Bull. We can understand the error. Uranus is so far from
the sun it looks like a star to the unaided eye. And it moves
so slowly; you have to watch for decades to realize that it
is a wanderer—or, in ancient Greek, a planētēs.
In
modern times, Uranus has become all but impossible to see.
The planet is naturally faint, and urban lights wipe it out
completely. No one notices when Uranus soars overhead.
Nevertheless,
you can see Uranus this month. Another planet will guide you
to it.
On
April 17th, 18th and 19th, Venus and Uranus are going to have
a close encounter in the dawn sky. Simply look east before
sunrise. As a guidepost, Venus can't be beat. It is so bright,
people often think it's a landing airplane. Simply scan Venus
with a pair of binoculars (or a small telescope) and you'll
see Uranus right beside it. If the sky is very dark, you may
be able to lift your eyes from the optics and see Uranus directly.
Note:
Uranus and Venus are so close together, they are
indistinguishable on the scale of this diagram.
On
April 17th the pair will be separated by about one degree,
the width of your pinky finger held at arm's length. On the
18th they'll be even closer together, 0.3 degrees. On the
19th the distance increases again to one degree.
The view through
a backyard telescope should be splendid. Diamond-bright Venus
has phases, and at the moment it resembles a tiny half-moon.
Uranus, meanwhile, is a little blue-green disk, clearly a
planet.
Set
your alarm and see what the ancients missed.
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Author: Dr. Tony
Phillips | Production Editor:
Dr. Tony Phillips | Credit: Science@NASA
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