Tonight's Sky September 2010
Text for Tonight's Sky September 2010
Your guide to constellations, deep-sky objects, planets and events.
Tonightʼs Sky, highlights of the September sky.
SEPTEMBER CONSTELLATIONS:
The September sky is for the birds!
The great constellation Cygnus, the swan, dominates the autumn evening.
Cygnus is also known as the Northern Cross.
This shape is easy to spot against the Milky Way, which stretches across the
September night sky.
Using bright Vega as your guide star, look for the cross just to the east.
Deneb, the swanʼs tail, is a supergiant star.
It has the luminosity of 160,000 Suns.
If Deneb replaced the Sun in the center of our solar system, it would engulf Mercury and Venus.
Albireo, at the head of the great bird, is a showpiece for small telescopes.
This spectacular pair of stars features contrasting colors of sapphire and golden topaz.
Aquila, the eagle, was known to the ancient Greeks as the great bird of Zeus.
Altair, the brightest star in Aquila, is only 16 light-years from Earth.
Its fast rotation, less than 10 hours, distorts its shape.
Altair is the southernmost star of the Summer Triangle, along with Deneb and Vega.
SEPTEMBER DEEP SKY OBJECTS:
Cygnus and Aquila are found in the overcrowded Milky Way area overhead.
On a clear night, hazy patches of nebulae can be seen by casually panning across theCygnus area with binoculars.
The most prominent is the North America Nebula, an area of gas and dust illuminated by the nearby, brilliant star, Deneb.
Cygnus also hosts several clusters of stars.
The easiest to find are M-29 and M-39.
M-29, when viewed at low power with a small telescope, resembles a small square.
It is found near the center of the Northern Cross.
Best seen with binoculars, M-39 is a loosely bound cluster of about 30 stars, just to the north of Deneb.
Use binoculars to look for the Coathanger, located halfway between Altair and Alberio.
From our viewpoint, these stars create a familiar pattern.
SEPTEMBER PLANETS:
Just before sunset in the west, Mars, Venus, and Saturn make their final appearance before heading behind the Sun.
Opposition occurs when a planet is opposite the Sun with Earth in between.
Jupiter reaches the point in its orbit closest to Earth during opposition, so it appears large and is visible all night long.
This is the best time to observe the planet with binoculars or a small telescope.
SEPTEMBER EVENTS:
During the summer, the Sunʼs path appears high in the sky and the days are long.
On the day of the equinox, the Sun rises exactly in the east and sets exactly in the west, and day and night are of equal length.
The autumnal equinox, heralding the beginning of the change in seasons from summer to fall, occurs at 10:09 Eastern Daylight Time on September 22nd.
After the equinox, the Sun will appear lower and lower in the sky, and the days will grow shorter.
These changes are due to the tilt of Earthʼs axis as it travels around the Sun
The full moon closest to the autumnal equinox is known as the Harvest Moon.
It rises in the east just before the end of twilight.
The extra moonlight lengthens the twilight to give farmers more time to harvest their crops.
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