When is the best time to see meteors?
August!
The Perseids showers start in the last week of July, peak on the
morning of August 12th, and finish about a week later.
This is an appropriate time to review some of your observational astronomy and teach you more.
During this time of the year the Earth passes through the orbit of the comet called
Swift-Tuttle. This comet has a period of 130 years (it's a short
period comet) and was last at perihelion in 1992. The materials
of this comet have spread out over its entire orbit and each year
we can count on a great show.
Here's a view of the sky overhead a few minutes after the midnight of August 12th. You should be able to spot the Great Summer Triangle. I want to draw your attention farther east towards the two constellations you learned last month, ANDROMEDA and PERSEUS. Can you find them in this image? The radiant for this shower is in the constellation of PERSEUS so this is called the Perseids meteor shower. Take your time and try to find ANDROMEDA and PERSEUS before paging down. | ![]() |
Here they are!
I've also drawn TRIANGULUM but I have not drawn in all the stars of ANDROMEDA (as I did last month) in order to keep the image tidy. Besides, there are no hard rules as to how to draw constellations. It is better (easier) to think of ANDROMEDA as a line of fairly bright stars with a northward pointing branch. You can use Vega and Deneb as pointer stars to ANDROMEDA. I've labeled ANDROMEDA's three brightest stars (Alpheratz,
Mirach and Almaak). Mirach and Almaak sort of point to Algol in the constellation of PERSEUS.
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Remember, this image is for fairly late at night because you have to stay up pretty late to see the best showers. A Full Moon or any other bright lights can make the showers less impressive. Of course, cloud cover can ruin even the best meteor showers so try to get out and see the showers several times throughout early and mid-August. At its peak the Perseids have a ZHR of around 100 so you should see one every minute or so! Just look towards Algol.
OK. What's that area of sky between ANDROMEDA and the Great Summer Triangle? Slightly south.
That's the Winged Horse, PEGASUS and, as constellations go, it's
a cheater! It steals Alpheratz from ANDROMEDA in order
to complete its most obvious feature - the Square of Pegasus.
Algenib is a B-type star about 520 light-years away and
with a luminosity of 1300 Suns. Markab is also a
B-type star (barely - it's B9) but is only 100 light-years away
and only 75 times as luminous as the Sun. The really beautiful
star in the Square is Scheat. [And now you know why I don't try to teach you pronunciation! Now that you can identify PEGASUS, you can start your star gazing this month and watch as these constellations rise on the eastern horizon, one by one. | ![]() |
Soon after sunset you should be able to find the Great Summer Triangle overhead in the northern sky. To its east you will find PEGASUS, easily identified by its Square. As the night progresses PEGASUS will seem to drag ANDROMEDA above the horizon and you can enjoy a countdown towards PERSEUS as you watch Alpheratz, then Mirach and then Almaak rise above the horizon. As ANDROMEDA progresses across the sky you will see that Mirach-Almaak points to the spot where Algol will appear. As Algol rises you will see PERSEUS slowly appear. Give PERSEUS a chance to get well above the horizon. By that time you should have seen many meteors (in early to mid August).
Great! But meanwhile, what are those other constellations in the southern part of the sky?
Those are constellations well worth learning. Indeed, you can work on these while you wait for ANDROMEDA and PERSEUS to rise.
Here's a view of the southern horizon just after sunset. (Not around midnight!)
You should recognize the stars I've labeled and recall that Spica is the bright star in the constellation of VIRGO. Tonight we will concentrate on those stars and constellations that appear below (to the south) of a line drawn from Spica to Altair. | ![]() |
Immediately following VIRGO is one of the more boring constellations, LIBRA (the Scales or the Balance). This is a difficult constellation to see because most of its stars are very dull. Its two brightest stars are only of magnitudes 2.6 and 2.7. Along with a pair of 3rd and 4th magnitude stars they form a four-sided figure that is meant to be a pair of scales.
LIBRA is best found
by first finding the next constellation behind it, SCORPIUS, the
Scorpion. SCORPIUS is a bright constellation and very easy to distinguish in the summer night sky.
In the Scorpion's heart lies its "star" star Antares
- a bright (magnitude 1) red (M-type) supergiant 330 light-years
away and 7500 times as luminous as the Sun. Closer examination
shows that Antares is a binary star. Its companion is very
dim (magnitude 5.4) and separated from the primary by only 2.7
arc seconds (at a PA of 273o) so you would need a good telescope to see the pair.
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The claws of SCORPIUS are part of an interesting story. At one time they included the stars in the constellation of LIBRA. The northern
most star in LIBRA is called Zubenelchemale which means
"The Northern Claw". The other bright star in LIBRA
is called Zubenelgenubi - "The Southern Claw".
Many years ago astronomers decided the ancient constellation of
SCORPIUS was too big so they cut off his claws to make LIBRA!
If you look at Zubenelgenubi with a pair of binoculars
you will see that it is a very nice binary. The 2.8 magnitude
primary is separated from its 5.2 magnitude secondary by 4 arc
minutes (not arc seconds) and that is a very good separation easy
to see with even a bad pair of binoculars (or a very good pair of eyes).
Behind SCORPIUS is another easy constellation, SAGITTARIUS.
This is supposed to be an archer but he looks like a teapot to me! Amateur astronomers with telescopes will find SAGITTARIUS is full of exciting objects including several star clusters (both open and globular), nebulas and binaries. You could see a lot here with a good telescope and some practice, but I will not be going into this kind of detail here. Besides, SAGITTARIUS is so low on the horizon that folks in the far north (north of Chicago) will not have a good view of it anyway. | ![]() |
Regardless, all astronomers should learn to recognize SAGITTARIUS. Just remember that the teapot is pouring (tea?) onto the scorpion's tail.
OK. Hey, what about all that space above LIBRA, SCORPIUS and SAGITTARIUS?
I was hoping you wouldn't ask! That's OPHIUCHUS and the two halves
of SERPENS. This is a "twisted" mess of constellations
but they take up a lot of sky and you really should know them. So, here goes.
OPHIUCHUS is a large dim C-shaped constellation with only one
bright star, Rasalhague. Like SAGITTARIUS below it, OPHIUCHUS
is full of interesting objects if you have a telescope or very
good binoculars. However, this is a boring constellation and hard
to identify because every book I have seen has its own way of
drawing in the lines!
Flanking OPHIUCHUS are the two serpents, SERPENS CAPUT (the Serpent's Head) and SERPENS CAUDA (the Serpent's Body). SERPENS CAPUT, to the northwest of OPHIUCHUS, actually does have a nice conspicuous triangular "head". | ![]() |
The Serpent's Body, SERPENS CAUDA, cuts across the body of OPHIUCHUS. (So imagine the line on the left is connected to the line on the right as it sweeps through the C-shaped OPHIUCHUS.) Here is a reverse color image you can print out.
The mythology of this area of the sky is interesting.
Aesculapius
(son of Apollo and Coronis) was a fantastic doctor with healing
powers so great that he could even bring the dead back to life.
Pluto, God of the Underworld, didn't like Aesculapius interfering
with such matters (because Pluto was getting lonely, what with
the lack of dead people to talk to ). So Pluto convinced Jupiter
(The God King) to zap Aesculapius with a bolt of lightning. After
the big zap, Jupiter felt bad for what he had done and placed
the spirit of Aesculapius in the sky as the constellation of OPHIUCHUS.
The next time you see a medical emblem (on a poster or pin) take
a good look at it and you will see that the shaft (representing
Aesculapius) has a snake or two wrapped around it - just like in the sky!
Use the image above to identify the stars and constellations visible soon after sunset, while you wait for PERSEUS to rise.
Here to the right, is the sky later in the night as the meteor showers start.
(Notice that Altair is in this image and the previous one so you can use Altair to link these two images together.) Use the Great Summer Triangle to get your orientation. Below Altair, you will find the (boring) constellations of OPHIUCHUS and SERPENS while farther south, along the southern horizon are SCORPIUS, LIBRA and SAGITTARIUS. As the night moves on and the sky rotates, you can focus your attention farther north and east as you watch ANDROMEDA and PERSEUS rise. Remember that Vega-Deneb points to the heart of ANDROMEDA and she follows the winged horse (PEGASUS) while she is followed by her husband (PERSEUS). Here is another reverse color image you can print out. | ![]() |
Astronomy is a good excuse to stay up late identifying stars and constellations while waiting for "shooting stars". So get out there and enjoy these wonderful, star-filled, summer nights!
See you next month.
Wishing you "Clear Skies".
Jamie (Dr Love)