Youth
Astronomy



What you will see on a clear night in July-August. 2008

What’s visible in July and August:

Constellations: Lyra, Cygnus, Aquila, Ursa Major (The Great Bear, which contains The Big Dipper), Bootes, Perseus, Cassiopeia, Scorpius and Sagittarius.

Double Stars: Albireo, Alcor & Mizar

Solar System: Jupiter & The Moon

Special Event: Perseid meteor shower, August 10-11

Summer is the best time of the year for stargazing. Lean back in a lounge chair with a pair of binoculars to become familiar with constellations and other star groups. Take your time observing stars and the Moon’s craters. Then use a telescope to examine fine details of the Moon, Jupiter’ (and four of its moons), as well as some double stars.


THE SUMMER TRIANGLE, a dramatic arrangement of stars, has replaced Orion the Hunter. Although technically not a constellation, the enormous Summer Triangle comprises three very bright stars high overhead.

The largest of the three stars is VEGA, which started to rise over the northeast horizon in early May. Vega, the third brightest star in the night sky--after SIRIUS and ARCTURUS--is in the western sector of the triangle. The remaining stars comprise DENEB n 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. 

During July and August, you will see the Summer Triangle move from the eastern sector of the sky to the western sector. 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 brightest star in the summer sky is Arcturus, replacing Sirius, the titleholder last winter. 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, the brightest star in the constellation BOOTES The Herdsman). 

That’s why some astronomers say, “Let’s arc to Arcturus.” Continue your imaginary line beyond Arcturus and you will spot another star, SPICA. Thus the expression, “Speed on to Spica!” once astronomers have found Arcturus.   




Ursa Major (Big Dipper)

Because of the Earth’s 24-hour rotation, THE BIG DIPPER is undergoing changes as well. The seven star group is still in the north and will remain so. Two months ago it was upside down (in the “pouring out” position), but now is standing on its bowl. The Big Dipper is a circumpolar grouping, which means that we see it year-round because it is close to the North Star.

Big Dipper  

 

 

 

   

Alcor & Mizar

Locate the Dipper’s bowl. If you draw an imaginary line beyond the two end stars of the bowl, you will find 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 is the lead star of the seven-star LITTLE DIPPER, which pours into the bowl of 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 (see Vacation Sightings).

 

 

 
 

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.

Jupiter

The largest of all the planets, JUPITER, appears this summer as a bright star above the southeast horizon. If you are 12 years old, you have something in common with this giant planet: the time you’ve been on Earth is the same time that Jupiter takes to orbit the Sun.

Did you know that there are 150 moons in the solar system? Because of the powerful magnetic fields of the four gaseous planets—Jupiter, Saturn, Uranus and Neptune—they have most of the moons. Because Jupiter has 65 moons, some observers refer to the giant planet as a mini solar system.

If you aim a telescope at Jupiter, you will see more than a white disc (as well as some parallel lines representing layers of gas). Look closely and you’ll spot the planet’s four largest moons. Jupiter’s remaining 61 moons are too small to be seen. 

Even though these four moons appear as tiny dots, they are about the same size as the Moon. They are always in a straight line because they are rotating around Jupiter’s equator. Usually they appear in two patterns: either three on one side and one on the other, or two on either side.

The four largest moons, called IO, EUROPA, GANYMEDE and CALLISTO, are also called the Galilean moons after Galileo who discovered them four centuries ago. You can Google the moons to learn about their surface features and size. For example, an ocean capped with fractured ice fields covers Europa.

On July 9 Jupiter will be at its brightest magnitude this year, as it will have reached opposition—directly opposite to the Sun.  The fifth planet from the Sun is a huge gas ball of helium and hydrogen. Its diameter of 143,000 km is so big that 11 Earths could fit across it. To put it another way, its volume would contain as many as 1,300 Earths.

Jupiter will remain above the southern horizon near the constellation SAGITTARIUS (shaped like a teapot) and SCORPIUS (looks like a fish hook).


The Moon

The brightest object in the night sky--some astronomers say the most rewarding—is THE MOON. Between July 4-18 and August 2-16, you’ll see the Moon display it’s early phases from crescent, to first quarter and then full 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 phase will appear in the west, the quarter phase in the south and the full Moon in the east.

Did you know that the Moon’s craters are the result of our closest celestial object being pummelled and battered by giant space rocks or asteroids? 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.

Vacation Sightings

Have you ever been to a cottage or a camp in the summer and gazed at a band of stars that snakes across the sky? That is the MILKY WAY--our home galaxy. You were seeing the galaxy edge-on, similar to looking edge-on at a dinner plate.


Since it is impossible to view the Milky Way in such a dramatic way in the city because of light pollution, make sure you have a look at it while you are on vacation with your family. (Technically speaking, the handful of stars you see year-round in your backyard are part of the Milky Way, but they pale in comparison to what you’ll see at the cottage or camp).  

The best way to scan the Milky Way is to lie on the grass, the beach or the boat dock and look straight up. With your naked eye you will see thousands of stars. However, using binoculars, you can view thousands more.

Note how the Milky Way cuts right across the Summer Triangle. If you are at a cottage or camp, the Milky Way will likely bury the Summer Triangle!

Professional astronomers estimate that our galaxy consists of more than 200 billion stars. Some of you may ask, “If there are that many stars in the Milky Way—and each star is a sun--how come we’re not blinded by the bright light of so many suns?” That’s because 99% of the light is hidden by dust and gas in the Milky Way. 

All astronomy books contain overhead illustrations of the Milky Way, showing it as a spiral galaxy. Granted, it’s impossible to make out the galaxy’s 200 billion stars. But here’s an easy way to grasp that number: if you represent just one star with a single grain of sand, then a heaping wheelbarrow of sand would represent 200 billion stars!

If you can get your hands on a star wheel (planisphere), you will discover that the largest portion of the Milky Way appears at the southern horizon in summer. If you rotate the planisphere all the way around, the galaxy will change position in the sky. That’s because we see the Milky Way in different parts of the sky as the Earth travels around the Sun.

As mentioned above, Arcturus is the main star in the constellation Bootes. From your backyard this star is big, but all by itself. From the cottage, however, the five remaining stars of Bootes pop out.

If you can find a hill that overlooks the southern horizon, you’ll be able to spot two constellations that make up the widest part of the Milky Way, Scorpius (The Scorpion) and Sagittarius (The Archer). Between these two constellations is the galaxy’s centre.

Directly overhead the Milky Way cuts through the Summer Triangle. To the north the Milky Way passes through a W-shaped constellation known as CASSIOPEIA. Finally, as you count the seven stars of the Big Dipper, see if you can locate all seven stars of the Little Dipper as it pours into the big one.

If you’re on vacation on August 11-12, and the sky is clear, look straight up and you’ll likely be treated to a rare celestial event: the PERSEID METEOR SHOWER. Even though the meteor shower may be seen in various parts of the sky, it will generally originate in the northeast in the area of the constellations Perseus (The Hero) and Cassiopeia (The Queen).

Some observers refer to a meteor shower as “shooting stars.” In fact, the shooting stars are not stars at all, but tiny sand-size meteoroids that burn up in the Earth’s atmosphere. The Perseid meteor shower is the most popular because it occurs in mid-summer when weather is ideal for skywatching. 

If you’re lucky, you might even see fireballs, which are very bright meteors that leave a smoke trail. The best way to observe the Perseid meteor shower is from a lounge chair.