This work was created by Dr Jamie Love and Creative Commons Licence licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

The Winter Southern Sky

by Dr Jamie Love Creative Commons Licence 1997 - 2011

In this lesson you will learn about the stars and constellations along the southern horizon that are visible soon after sunset during the winter months. This will "complete" our lessons in observational astronomy because we will now have gone full circle and we will return to some familiar constellations that you learned long ago (like ORION).

After a December sunset you will find that SAGITTARIUS is on the western horizon. You will recall that this is one of the easiest members of the Zodiac to identify. It's shaped like a teapot. After SAGITTARIUS comes four dim, poorly defined Zodiac constellations - CAPRICORNUS, AQUARIUS, PISCES (with the circlet of PISCES the only easily identified feature) and ARIES. Then, on the eastern horizon we find that familiar TAURUS is on the rise.

Yeah. We already covered them. What about all that space to the south of the Zodiac?

That space is our topic for this lesson. Throughout these lessons I have emphasized stars and constellations seen from the Northern Hemisphere. However, unless you live at the North Pole, you will have seen a large portion of the Southern Celestial Hemisphere too. Recall that the Celestial Equator (the Earth's equator projected into the sky) passes through ORION's belt and that Rigel is actually in the Southern Celestial Hemisphere. Rigel has a declination of -8o. Portions of VIRGO, PISCES and AQUARIUS, and all of LIBRA, SCORPIUS, SAGITTARIUS and CAPRICORNUS, are in the Southern Celestial Hemisphere and thus have negative declinations. In this lesson and the next we will focus our attention on the southern sky. Naturally, the further north you live the less of the Southern Celestial Hemisphere is visible and if you are very far north, these stars won't be visible at all.

Assuming you aren't too far north you should be able to see the brilliant star Fomalhaut on the southern horizon. If you aren't sure about the position of Fomalhaut, start with the Square of Pegasus. Imagine a line from Scheat through Markab and extend it south to Fomalhaut. (Don't confuse it with Diphda which is further east. We'll get to that star in a moment.)

Fomalhaut is the only bright star in the constellation of PISCIS AUSTRALIS, the Southern Fish. This constellation is boring and small but Fomalhaut certainly isn't! This is a very white star (A-type) only 22 light-years away so it's one of our closest neighbors. It is also 13 times more luminous than our Sun, so it really stands out with a relative magnitude of 1.2. Several years ago astronomers discovered a cloud of cool matter around Fomalhaut. This dust ring may be similar to the accretion disk from which our Solar System formed.

If your latitude is far enough south you can continue that imaginary line through PISCIS AUSTRALIS and into the constellation of GRUS, the Crane. There are four "bird constellations" in the Southern Celestial Hemisphere, although none as big as CYGNUS. The Crane's brightest star, Alnair, is a bluish star (B-type) 68 light-years away and over 200 times as bright as the Sun, but with a relative magnitude of 1.7.

It's slightly dimmer (magnitude 2.1) neighbor, Al Dhanab, is a red giant (M-type) and is supposed to be the center of the Crane.

To the east of the Crane is the (boring) constellation of PHOENIX - a mythological bird that regularly bursts into flames but which rises each time from its ashes. Ankaa is the only bright (magnitude 2.4) star in this constellation and I haven't bothered to draw in the PHOENIX because it's so dull and most of it is below the horizon anyway. Slightly above PHOENIX is an even duller constellation called SCULPTOR but without a telescope or clear night this space just looks empty!

I can't see GRUS or PHOENIX. I'm too far north.
Isn't there anything else to see up here in the north? What about that big area of stars below PISCES?

That's CETUS, the Sea Monster, and there are several interesting things in this constellation.
[By the way, the name "Cetus" has been used for other variations of "sea monster" including "whale". All whales and dolphins belong to a group of animals called "cetaceans". Some star charts and books call CETUS "The Whale". That's fine. Historically, though, CETUS is a sea monster. I just thought you should know. ]

Before learning about CETUS, use this image to remind yourself about the Southern Fish and Crane. Can you find them? If not, page up and have another look.
You should be able to find PISCES too, arching east starting below the Square with its "circlet of PISCES" as a clear feature to get you started. Notice that the stars in PISCES arch south and then swing back north as if to make a "V" pointing towards our target (CETUS). Also, recall that AQUARIUS is in front of PISCES and AIRES is behind it. (They are all in this image.)

Some people find CETUS by simply looking south of the two brightest stars in ARIES - Hamal and Sheratan. I think it's better to find CETUS by starting with the Square of Pegasus. Imagine a line from Alpheratz through Algenib and continue south to the orangish star Diphda.

Diphda is the brightest (magnitude 2) star in CETUS. Once you have identified Diphda you have found the tail of the whale (or sea serpent). Sweep eastwards (towards the left) along a series of stars that end in Menkar, a red star of magnitude 2.5 that sits in the nose of CETUS. Between Diphda and Menkar, but closer to Menkar, is a very unusual star called Mira. It, too, is a reddish star and it might be as bright as Menkar, or so dim that you cannot see it at all! I'll explain why in a moment.
Notice that I've draw CETUS such that all the lines seem to go through mysterious Mira. As I've said before, there is no "law" to follow in drawing a constellation's lines. I just use what I like! Here I have CETUS as a multi-legged creature. Some folks make a whale out of these stars and others make a twisted serpent.

Tau Ceti, is an ordinary looking star on one of CETUS' legs. It is about a third as luminous as our Sun yet it is so bright in our night sky (magnitude 3.5) that you would be right to guess that it is very close. It's less than 12 light-years away. Tau Ceti is a G-type star, similar to our Sun. That makes Tau Ceti interesting because astronomers are eager to discover if it has a solar system like our own. That would make it a good "candidate" for colonization. Astronomers have spent many hours listening to this star for signs of intelligent radio signals. Unfortunately, if there are "Tau-cetians", they aren't talking!

To amateur astronomers the most important star in CETUS is Mira. In my drawing, Mira can be found by following any of CETUS' legs up to the center where the other legs join, but Mira is not always so easy to find. Perhaps you will recall that there was a bright star in some of my images of PISCES, just south of where the "V" of PISCES bends back northward, but that star was missing from other images! That was Mira and now an explanation is due.

Mira is a long-term variable star. Indeed, it was the first variable star discovered. You have learned about other variable stars - the eclipsing variables like Algol and the pulsating variables like the Cepheids. Mira, and other long-term variables, are more like a Cepheid because their fluctuations are caused by the stars' actual brightening and dimming. You will recall that Cepheids are yellow supergiants with very regular periods and the length of a Cepheid's period is so constant it gives us an idea about that star's absolute brightness and thus its distance. Cepheids are short-term pulsating stars.
Long-term variables, like Mira, are a different kind of pulsating star. They are red giants or supergiants with periods (length of time between maximum brightness) of at least 80 days. That's why they are called long-term. The amplitude of their pulses (their brightness) is not very constant and even their periods are pretty variable.

Mira is classified as a "pulsating M-type supergiant". The "M-type" designation means it's a nice reddish color and the name "supergiant" says it all. This star is more than 100 times as large as our own Sun! Mira is pretty close to us too - a mere 95 light-years away.

Of course it's the "pulsating" part that makes this star interesting.

Recall that red giants are very old stars approaching the end of their lives. Unlike normal stars, red giants have a core full of helium. When this helium starts to undergo nuclear fusion, the star becomes unstable and begins to experience waves of energy fluctuations that cause it to expand and contract. This causes the star to brighten and dim over time. Many red giants fluctuate. For example, over the past few years the magnitude of Betelgeuse (in ORION) has ranged from 0.1 to 0.9. However, unlike Mira, Betelgeuse's magnitude fluctuations are not periodic (just weird ).

Not that you can set your watch to Mira's fluctuations. Unlike an eclipsing variable (like Algol) long-period variables are more, well, "variable". We don't fully understand the physics of pulsating stars like Mira so we really cannot make accurate predictions about when it will be at its maximum brightness. Mira's period is an average of 331 days and it reach its maximum in early September 2001. So you can use that date to estimate that Mira will be at its brightest one month earlier than September for each year past 2001. However, that timing can be a bit off so be sure to have a look for Mira frequently. This star is full of surprises! It has been known to grow to a magnitude as high as 1.7 making it the brightest star in CETUS. Usually it tops out a whole magnitude dimmer than that and during some cycles it never gets any brighter than 4th magnitude.. That's still bright enough to be seen with the naked eye. However, its magnitude can be as low as 10 during its minimum so there may be times when you cannot see it at all without optical aids.

Perhaps that is why Mira is such an exciting star. Amateurs consider it a challenge to find and enjoy keeping track of it. They will find Mira at a time of maximum brightness and then, over the course of the many months, they will follow its dimming as it becomes a telescope-only object. Then they watch it brighten again, like an old friend coming home. Mira is certainly a good "excuse" to get a telescope and a wonderful star on which to practice telescope methods, but even without a telescope you can enjoy Mira.

Because Mira's period is 11 months it's impossible to follow it all year round.
(The Sun eventually overwhelms the view.)

CETUS is topped with a nice group of stars that form its head and you might be able to use those stars to help get you oriented towards Mira. The brightest star in CETUS' head, Menkar (magnitude of 2.5), is a red giant similar to Mira, in color but not a variable (although some folks claim it is slightly variable).
Menkar is 130 light-years away and has a declination of +4 while Mira has a declination of -2.

So the Celestial Equator passes through the throat of CETUS.

Right. It's a good idea to try to remember a few constellations that slip across both hemispheres. That keeps you oriented. I told you (back in February) that the Celestial Equator passes through ORION. About an hour after sunset (in December) you will see ORION rise and see that we have completed our lessons by completing our circle of the sky.

Wait a minute. What about all the space between CETUS and ORION?

Most of that space is ERIDANUS, the (wandering) River. Before I show it to you, let's take a peak at what is rising in the east as the evening progresses and do a little reviewing.

Here's a view towards the south and slightly east a couple hours after sunset in December. You should be able to identify (easily) three outstanding constellations on the left. It's been a long time since you've seen them but try to recall the patterns. I've colored in two of the reddish stars to help you.

On the right side of this image is CETUS but it is seen here at a very steep angle. I've colored in the three orangish/reddish stars of CETUS (including Mira) to help you. However, in this image I have cut off the stars I suggested you use to guide you to CETUS! I'm not trying to be cruel. I just want you to try your mind at this image.

Can you find CETUS? Can you draw in some of the features? Have a good look at this image before paging down.

I hope you were able to find these constellations.

ORION should be firmly fixed in your mind. Rigel and Betelgeuse really stand out. The stars in ORION's belt point northwards (up) to Aldebaran in TAURUS and southwards (down) to Sirius in CANIS MAJOR.

CETUS may have been more difficult. Don't feel bad if you missed it. Instead, use this image to help you discover new ways to find CETUS. Do you see that TAURUS makes a nice pointing device to CETUS? You might have identified Sheratan (but without Hamal in the image it would have been difficult) and understood that CETUS was south of there. By the way, most of PISCES is missing but its "V" is in the image and pointing towards Mira.

Yes, yes. But what about all that blank space?!

Ah yes, ERIDANUS, the (wandering) River. It's a real mess and there must be a hundred ways to draw it.

I like to start at Cursa (sometimes written as Kursa) because it's that bright star north of Rigel. It also happens to be the brightest star in ERIDANUS that you can see from this far north. Cursa is an A-type star, 83 times as luminous as the Sun and 96 light-years away.
ERIDANUS drifts towards CETUS but heads south to Zaurak along the way. This is the second brightest star in ERIDANUS that you can see from the north and I like to use this star as the point towards which one of ERIDANUS' tributaries wanders. Zaurak is type M (so it will appear a little redder than in this image) and 120 times as luminous as our Sun but 114 light-years away. ERIDANUS then continues towards CETUS picking up Delta () and Epsilon () Eridani along the way. Just before in reaches CETUS, ERIDANUS dives south in a series of arches that lead below the southern horizon.

But that's not all of ERIDANUS. There is plenty more of this constellation farther south and be sure you fill in some of the other tributaries - especially the long one that starts near Rigel.

By the way, Delta () Eridani is sometimes called Rana and it's a K-type star 2.6 times as luminous as our Sun and a mere 29 light-years away. This is a pretty star in a pair of binoculars but Epsilon () Eridani is more interesting. It's only 10.7 light-years away and has been given a lot of attention by astronomers seeking extrasolar planets (planets orbiting stars other than our own). Van de Kamp, the fellow who said he detected a wobble in Bernard's Star, compiled date which indicated that Epsilon () Eridani has a wobble too! IRAS (which, you'll recall from last month's lesson, is the satellite that detects infrared) discovered there was a cool mass of materials around Epsilon () Eridani. In 1998 the James Clerk Maxwell Telescope produced a (computer enhanced) image indicating that there is a disk of material orbiting about 50 Astronomical Units (AUs) from this star. This dust ring might be a young solar system in the making! Some interpretations of the data say that there is a planet, twice the mass of Jupiter, orbiting Epsilon () Eridani at a distance of 5 AUs and with a period of 5 years. Epsilon () Eridani has a magnitude of 3.7, so it's easy to find, and it is a type K star - so it's like Delta () Eridani but dimmer.

I'll look for it. What's below ORION, to the east of ERIDANUS?

Immediately below ORION is LEPUS, the Hare. I've drawn the Hare to show off its ears (and a "leg?" growing from its back!) but on a poor night all you see are the four brightest stars forming a box. LEPUS' brightest star Arneb is an F-type supergiant 6800 times as luminous as the Sun and at a distance of 950 light-years. Nihal is a G-type star 316 light-years away and about 600 times as luminous as the Sun. Arneb is of magnitude 2.6 and Nihal is 2.8.

Below LEPUS is COLUMBA, the Dove. Older books call it COLUMBA NOAE meaning "Noah's Dove". There is little in this dove to see but I have labeled Phaet because it's so bright (magnitude 2.6). Also, notice that the Dove does not extend to that bright star in the far left of this image. (That's Furud in CANIS MAJOR.)

Below ERIDANUS, and not labeled, are the small, dull constellations of CAELUM and HOROGIUM. On the other side of ERIDANUS and below CETUS are the equally boring constellations of FORNAX and SCULPTOR. In the 18th century a fellow named Lacaille put names to a whole bunch of small, southern constellations. These four, and a couple others, are all his fault (not mine)! Frankly, I think the guy was doing his best to make himself famous by naming more constellations than anyone else. He made them small so there were lots of them. [Don't get me started about Lacaille! ]

OK! OK! Besides, these are too far south for me to see anyway. Why learn stars you cannot see?

Well, I don't like Lacaille one bit but I don't think you should limit your education only to stars you can see. As a matter of fact, in our next lesson I will teach you the stars of the extreme south. You may never see them, but I bet you have heard of, Alpha-Centauri. Maybe you've heard of the constellation called the SOUTHERN CROSS. All these, and more, will complete your education in observational astronomy (even though you may never observe them yourself). Who knows - maybe one day you will travel to the south and see these sky sights.



This work was created by Dr Jamie Love and Creative Commons Licence licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.