Having just consumed
the Galileo spacecraft with less effect than a lone pea going into the belly
of the Jolly Green Giant, the planet Jupiter has entered the celestial stage
of our pre-dawn sky. It is one of four players in a somewhat fleeting parade
of planets this week.
For a brief few minutes before dawn Wednesday from some locations, Jupiter joins elusive Mercury low in the eastern sky, while a thin crescent Moon hovers between them and slightly to the left.
The group will sit within a circle of sky less than 10 degrees
across. In lay terms, you'll be able to blot them all out with your fist on
an outstretched arm.
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| SKY MAP: The eastern horizon before dawn on Wednesday, Sept. 24. The map works on subsequent mornings, too, sans the Moon.
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Mercury will only be visible to those who have an unobstructed view of the horizon, however. It rises at about between 5 a.m. and 5:30 local time at many U.S. locations. The planet of course fades with dawn. By the weekend it rises later, does not get as high, and becomes a very difficult object to find.
The Moon is but a sliver Wednesday morning. On Thursday, it reaches its new phase, when it is not visible at all.
Jupiter, meanwhile, is entering a long stretch of fine viewing opportunities. It has been sneaking above the eastern horizon just before dawn since early September and is now reasonably easy to find. The gas giant planet rises higher and higher into the pre-dawn sky through the end of the year.
Saturn is already high in the east in the early morning hours. Look for it well above and slightly to the southeast (right) of Jupiter. If you're able to find Mercury, draw an imaginary line from it to Saturn and you'll see it passes through Jupiter. This line is the ecliptic, along which the planets, the Moon and the Sun all roughly adhere as they move through our sky. The ecliptic represents the main orbital plane of the solar system.
A small telescope will reveal Saturn's rings and
one or more of Jupiter's four largest Moons. These Galilean moons -- Io, Europa,
Ganymede and Callisto -- are named for their discoverer, Galileo Galilei, also
namesake of the NASA space probe whose mission ended abruptly Sept. 21 in a
planned death
dive into Jupiter.
Mid-sized backyard telescopes allow one to see the
colorful cloud bands of Jupiter.
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Elusive
Mercury
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Mercury's
local rise times for select cities on Wednesday, Sept. 24.
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Boston
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5:04 a.m.
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Chicago
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5:11 a.m.
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Denver
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5:22 a.m.
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Los Angeles
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5:21 a.m.
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New Orleans
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5:30 a.m.
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New York
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5:18 a.m.
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Philadelphia
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5:23 a.m.
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Seattle
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5:24 a.m.
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Rise
times in your area can be generated at the Old
Farmer's Almanac Web site.
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The night sky changes
constantly with the seasons, and right
now the early morning eastern sky is loaded with bright stars, including four
of the 10
brightest. Among these, to the southeast
is Sirius,
the brightest star in the sky. Sirius shines at magnitude -1.47 on an astronomers'
scale in which lower numbers represent brighter objects.
The brilliance of Sirius is just shy of Jupiter's, which shines now at magnitude -1.73. Mercury is at magnitude 0.02 and Saturn at 0.11.
Once you've located all these objects, using the
map near the top right of this page, you can employ them as guides to help you
find other nearby bright stars, including Rigel,
Procyon
and Betelgeuse.
Mars, meanwhile, remains the most alluring object in the night sky, shining at magnitude -2.28. It is well up in the southeast at sunset and rises into the southern sky around midnight, then sinks to the southwest and sets at about 4 a.m.
You don't need a map to find Mars -- it's the brightest object in the night sky other than the Moon.
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Make Your Own Sky
Charts
Learn how Starry Night can help you explore the universe from your desktop.
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Degrees
measure apparent sizes of objects or distances in the sky, as seen from
our vantage point. The Moon is one-half degree in width. The width of
your fist held at arm's length is about 10 degrees.
1 AU, or astronomical
unit, is the distance from the Sun to Earth, or about 93 million miles.
Magnitude is
the standard by which astronomers measure the apparent brightness of objects
that appear in the sky. The lower the number, the brighter the object.
The brightest stars in the sky are categorized as zero or first magnitude.
Negative magnitudes are reserved for the most brilliant objects: the brightest
star is Sirius (-1.4); the full Moon is -12.7; the Sun is -26.7. The faintest
stars visible under dark skies are around +6.
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