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Royal Astronomical Society of Canada.
This page was last modified on: October 2nd, 2017.
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What you will see on a clear night
Shorter days and dropping leaves are sure signs we have entered fall. Another sign: the way some constellations are shifting to the west, as though drawn by a giant magnet.
Now that we’re experiencing cooler weather, it’s time to
put on a sweater or a jacket and become familiar with constellations
and other star groups with the naked eye, as well as fine details of
the Moon using binoculars.
Even though summer has come and gone, the SUMMER TRIANGLE--a dramatic arrangement of stars—is still with us. Although technically not a constellation, the enormous Summer Triangle comprises three very bright stars that were high overhead in July and August. Since then, these stars have moved a little to the west.
The brightest of the three stars, VEGA, is in the western sector of the triangle. The remaining stars comprise DENEB in the northern sector and ALTAIR in the south.
The three stars of the Summer Triangle are part of three constellations. Vega is in LYRA (The Lyre), Altair is in AQUILA (The Eagle) and Deneb is in CYGNUS (The Swan). Deneb serves as the swan’s tail while the star ALBIREO at the far end is the swan’s head. The wings are at right angles to the body.
Cygnus is also known as the NORTHERN CROSS due to its shape. The swan’s wings double as the arms of the cross while the swan’s body doubles as the cross’s shaft.
Albireo at the south end of the swan (or the cross) within the Summer Triangle) is a double star. You will need binoculars or a telescope to pick out two stars of different colours; one is blue (hotter than the Sun) and the other is yellow (similar to the Sun, although somewhat cooler).
Amateur astronomers use a special trick with their telescope to accentuate the colour of a star; they adjust their focus knob so that the star goes out of focus. Vega is a prime example; by putting it out of focus, you will see that it is a bluish-white star.
The Summer Triangle has moved from the eastern sector of the sky (in May) to the western sector because most constellations relocate from east to west as the Earth rotates around the Sun. Star groups such as the Summer Triangle and constellations such as ORION, which are well below the NORTH STAR, rise above the eastern horizon and then disappear below the western horizon during a portion of the year. Orion will return next winter at which time The Summer Triangle will disappear.
The most popular group of stars is the Big Dipper. All you have to do is look north and there it is; a four-star bowl with a three-star handle.
The seven-star Big Dipper is in the constellation Big Bear. The Big Dipper is a well-known group of stars as it can be seen year-round. This is because it is close to the North Star (Polaris), making it a circumpolar grouping.
Most constellations like Orion and the Summer Triangle are known as seasonal constellations because they are far from the North Star and slip beneath the western horizon after travelling for a few months across the night sky.
The Big Dipper can be used to find the NORTH STAR. First, find the bowl. Then draw an imaginary line up and beyond the two end stars of the bowl and you will locate the NORTH STAR. Many people think that the North Star is the brightest in the night sky. Not true! It’s way down on the brightness scale.
The North Star (which remains in one spot year-round) is the lead star of the seven-star LITTLE DIPPER, which pours into the Big Dipper. But you have to be at a very dark site—like a farm or a cottage away from city lights—to be able to make out the Little Dipper.
There is something unique about one of the seven stars of the Big Dipper. Look carefully at the second star from the end of the Dipper’s handle and you’ll spot a double star, ALCOR & MIZAR. The star duo is more definitive with binoculars or a telescope.
The brightest star now in the night sky (as it was in summer) is Arcturus, replacing Sirius, last winter’s titleholder. Here’s how you find Arcturus: First, locate the BIG DIPPER high overhead. Then draw an imaginary arc-shaped line beyond the handle of the Big Dipper and you will see Arcturus.
That’s why some astronomers say, “Let’s arc to Arcturus.”
don’t wait too long to find it as it disappears over the western
horizon in late September.
SATURN appears throughout Sept. and Oct. as a bright "star" in the southwest.
will need a telescope to find Saturn’s dramatic rings. If you see a
"star" next to the planet; that will be Titan, the largetst of
its moon family. Titan is about 50 percent larger than our Moon.
Saturn is the sixth planet from the Sun. Is there anyone in your family 30 years old? That’s how long it takes the ringed planet to orbit the Sun. Although the gaseous planet appears tiny in a telescope, it is the second largest planet in the solar system. It would take 10 Earths to span Saturn’s diameter and 20 Earths to span its rings.
Some astronomers say the most rewarding object in the night sky is
the MOON. Between Sept. 6 and Oct. 27, you will see the Moon display
its early evening phases.
- Sept. 24 and Oct. 24 crescent Moon
Craters and "seas" (the grey areas of the Moon) can be
easily picked out with binoculars or a low power telescope. The secret
to viewing the night sky with binoculars is to keep them as steady as
possible: either mount them on a tripod or sit back in a lounge chair.
Where to look for the Moon after sunset? The crescent
appear in the southwest, the quarter phase in the south and (as
mentioned above) the full Moon in the east.
Did you know that the Moon's craters are the result of
celestial object being pummelled and battered by giant space rocks or
asteroids billions of years ago? If the Moon had an atmosphere, the
craters would have long eroded away from wind and water erosion like
what happened here on Earth. But because there is no atmosphere on
the Moon, the craters have not changed ever since they were formed.
The Moon’s craters and mountains are most dramatic if you look near the terminator—the line that separates the dark side from the sunlit side. That’s because the shadows created by the Sun are the longest. If you look through a telescope, you can even spot crater walls disappearing into the shadows.