The Fundamentals of Stargazing Sky Tours South

01 – The March Sky

The Constellation Orion Let’s begin the tours of the deep-southern sky with the most famous and unmistakable constellation in the heavens, Orion, which will serve as a guide for other bright constellations in the southern late-summer sky.

Head outdoors around 8 or 9 p.m. on an evening in early March, and turn towards the north. If you can’t find north, you can ask someone else, or get a small inexpensive compass, or use the GPS in your smartphone or tablet. But you need to face at least generally northward before you can proceed. You will also need a good unobstructed view of the sky in the north, so you may need to get away from structures and trees and so on.

The bright stars of the constellation Orion (in this map, south is up and east is to the right)

And bring a pair of binoculars if you have them, though they are not necessary for this tour.

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Now that you’re facing north with a good view of a clear sky, make a 1/8th of a turn to your left. Now you are facing northwest, more or less. Turn your gaze upward about halfway to the point directly overhead. Look for three bright stars in a tidy line. They span a patch of sky about as wide as your three middle fingers held at arm’s length. This is the “belt” of the constellation Orion. In the northern hemisphere, where Orion was first conceived by the ancient Greeks and other classical cultures, these stars depict a hunter standing upright adorned with a belt and sword and holding a westward facing shield in his left hand and an upraised club in his right. In the southern hemisphere, the constellation appears upside down as if he is doing a cartwheel.

Note: The descriptions in this tour are accurate for 35 degrees south latitude. If you live north of this latitude, Orion will appear slightly farther above the horizon. If you live south of this latitude, the stars appear lower in the sky.

For southern-hemisphere observers, well below Orion’s Belt closer to the horizon, lie two brighter stars. The brighter star to the right is clearly orange-red. This is the star Betelgeuse (“BAY-tell-jewz”). It marks one of the shoulders of Orion. The left star is whitish-blue and goes by the name of Bellatrix.

Above the belt lie two more bright stars marking Orion’s feet. The brilliant blue star to the west is Rigel (“RYE-jel”). The eastern star is called Saiph (“safe”).

Take a moment to marvel at this splendid constellation. Glittering like a gigantic tapestry of celestial jewels, the constellation holds a number of the brightest stars in the sky in close proximity to each other. Many of these stars formed at the same time from the vast and invisible mass of gas and dust in this part of the sky. As you will see shortly, new stars are being formed here even now.

The bright red-orange star marking Orion’s shoulder, called Betelgeuse, is a massive “red supergiant” star that’s burned through most of its fuel and is nearing the end of its life. It will explode, sometime in the next million years or so, as a supernova that shines so bright it will cast shadows by night and be visible in our daytime for several weeks. At present, the core of the star has shrunk and grown hotter, which in turn has caused the outer layers of the star to expand. So Betelgeuse is immense: if it were to replace our Sun at the center of our solar system, the visible surface of the star would extend to the orbit of Jupiter! You will learn more about how stars evolve through their lifetimes later in this program.

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Image of the star Betelgeuse (credit: NASA)

Betelgeuse lies about 650 light years from Earth, which means the light you see now has been travelling towards Earth for 650 years. One light year, the distance light travels in a year, works out to a distance of about 6 trillion miles.

Rigel (“RYE-jel”), which marks one of the feet of the inverted celestial hunter, is on the other side of the evolutionary scale. This star is massive, like Betelgeuse, but it’s much younger and still burns hydrogen in its core. So its core is cooler, its outer layers more compact, and its surface is hotter (12,000 K) than Betelgeuse (3,500 K). Rigel is also slightly brighter than Betelgeuse. Indeed, only five stars in the entire sky outshine Rigel.

Three stars lined up in a tidy row mark Orion’s Belt. These stars are, from east to west (or right to left) Alnitak, Alnilam, and Mintaka. Like Rigel, these stars are also young, massive, blue- white stars. They will also end their lives, like most of the bright stars of Orion, in brilliant supernovae explosions in the distant future. These stars are a chance alignment: each lies at a different distance. Alnitak, Alnilam, and Mintaka are 800, 1340, and 915 light years from Earth, respectively.

If you have binoculars handy, turn them to Orion’s Belt to see many fine arrangements of bright blue-white stars, including a winding S-shaped group between Mintaka and Alnilam. Arab astronomers once called Orion’s Belt the “String of Pearls”, but in binoculars it looks more like a web of diamonds.

Halfway between and a little north (or below) the shoulders of Orion, look for the small patch of fainter stars that mark the hunter’s relatively small head. To your unaided eye, the patch may appear cloud-like and unresolved. If your eyes are keen, you may detect three stars here. These stars are called phi-1 Orionis, phi-2 Orionis, and lambda Orionis (also known as Meissa). If you have your binoculars handy, look at these three stars. Your optics will reveal a pleasant surprise: some 20-30 faint stars spread among the three brighter stars. Many are part of the same cluster of newborn stars.

Finally, look closely at the group of three dim stars that appear to extend upward from the belt. This is the so-called Sword of Orion. In binoculars or a small telescope, the middle star appears fuzzy and indistinct, because it’s entangled in a mass of glowing gas and dust called the Orion

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Nebula where a cluster of brand-new stars are in the process of formation. You will learn more about this nebula and other objects in Orion’s sword later in this month’s program.

As a constellation, Orion has been known since antiquity. The Sumerians depicted these stars as their legendary hero Gilgamesh. The starry hero was seen as fighting a celestial bull, the V- shaped congregation of stars now known as Taurus, which we will visit next.

Despite the prominence of these stars, the Greeks assigned them a less noble namesake. Orion was a mighty hunter, to be sure, but he was a bit of a dim-witted brute. One legend tells of the hunter madly killing the Earth’s animals until too few remained. The goddess Artemis put an end to Orion’s greed by sending the fearsome scorpion Scorpius to sting the hunter, killing him instantly. Another version of the legend has Orion pursuing Artemis with romantic inclinations before the virginal goddess unleashed the Scorpion. In both cases, Artemis regretted the death of the hunter and asked Zeus to place Orion and Scorpius in the heavens at opposite ends of the sky.

Orion’s Belt points the way to the constellation Taurus

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The Constellation Taurus Using Orion as a base of operations, you can now navigate to other prominent constellations hovering over the northern horizon. Extend a line from Orion’s Belt toward the northwest (the lower left as seen from the southern hemisphere in the mid-evening hours in March). You will arrive at a bright orange star just above the northwestern horizon. This is Aldebaran, the brightest star in the constellation Taurus, the Bull. Like Orion, Taurus was one of the 48 original constellations included in the maps of the ancient astronomer Ptolemy in the 1st and 2nd century A.D.

The bright star Aldebaran (“all-DEB-a-run”) is a swollen giant star some 45x the diameter of our own Sun. It’s far smaller and intrinsically fainter than Betelgeuse in Orion, but still appears bright because it lies just 65 light years away, about ten times closer than Betelgeuse.

A much smaller group than Orion, Taurus is still a lovely constellation. Along with Gemini, it is one of the northernmost constellations of the zodiac so in the southern hemisphere Taurus never gets very far above the northern horizon. This ancient constellation holds two open star clusters, the Hyades and the Pleiades, both of which are a magnificent sight with the unaided eye or with binoculars. The Hyades cluster is the little V-shaped group of stars to one side of Aldebaran. It is a large and nearby star cluster and one of the prettiest and easiest to observe with binoculars. This star cluster lies about 135 light years away, which means Aldebaran is not a member, but merely a foreground star.

The constellation Taurus; the Pleiades, the brightest star of which is Alcyone, is at lower left.

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The famous Pleiades star cluster lies a little further on the same line from Orion’s Belt through the “V” of Taurus. The cluster is a tiny dipper-shaped patch of stars smaller than your little fingernail held at arm’s length. You can see perhaps six stars in the cluster without optical aid. Alcyone is the brightest. Unfortunately, in the southern hemisphere, the cluster never gets very high above the northern horizon.

The V-shape of Taurus resulted in the mythical association of these stars with the head of a bull since at least 4000 B.C., and ancient Babylon, Egypt, and Greece noted these stars as a major constellation. The name “Taurus” means “bull” in Latin. The small patch of V-shaped stars marks the head of the bull. The star at the nose of the bull is gamma Tauri. Aldebaran marks the eye.

The Constellation Gemini Also low in the north in March, to the right of Taurus as seen from the southern hemisphere, lies the constellation Gemini. The constellation is marked by the two bright stars Castor and Pollux which form the heads of the two legendary twins. Their long bodies are comprised of two lines of stars that extend in the direction towards Orion.

If you’re unsure where to find Gemini, you can once again use Orion. Draw an imaginary line diagonally from Rigel past Betelgeuse about a distance equal to the separation of these two bright stars. This will land you smack in the middle of Gemini (see image below).

The twins of Gemini, according to Greek mythology, were sons of Zeus named Castor and Pollux, who together were known as the Dioscuri. Pollux was a boxer, and Castor a horseman and fierce warrior. The brothers proved their courage by joining Jason and his Argonauts on his quest for the Golden Fleece, among other adventures. Upon returning, Castor and Pollux met their fate during more sordid matters, falling into a murderous grievance with another pair of twins, Idas and Lynceus over rustled cattle. Castor was killed by Lynceus, who was in turn slain by Pollux.

Pollux grieved for his fallen brother and asked Zeus if the two could share immortality. It pays to have a powerful father: Zeus placed both in the sky as the constellation Gemini. The brightest stars of the constellation take the names of the twins.

Castor, which you’ll meet in the tour of the deep-sky this month, is a lovely double-star in a small telescope—a triple star actually. It’s the second-brightest star of the constellation. More detailed astronomical measurements reveal Castor as a 6-star system. The brightest star in Gemini, yellow-orange Pollux, makes a lovely color contrast with Castor.

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Using the stars Rigel and Betelgeuse in Orion to find the constellation Gemini

The rest of the “body” of the twin marked by Pollux consists of the star Wasat (which means “the waist”) and Alhena. His arm is marked by kappa (κ) Gem and his foot by xi (ξ) Gem. Castor’s mid-section is the star Mebsuta, while Teja and Propus mark his feet.

Gemini makes for pleasant viewing with binoculars. The region around Castor and Pollux are fairly sparse of background stars. But you’ll find a richer star field towards the feet of the twins, which is a particularly splendid region in binoculars, especially around the stars Tejat and Propus, which themselves almost impinge on the upraised club of Orion. In binoculars, it appears as if the twins have dipped their feet in a river of stars.

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Gemini lies to the northeast of the constellation Orion

The Constellation Canis Major Orion’s Belt guided us north and west to the constellation Taurus, and it also points the way, in the other direction, upward, to the constellation Canis Major, the Big Dog.

As you turn your gaze towards Canis Major, you will be immediately struck by a blazing blue- white star. This is Sirius, the brightest star in the heavens, and it marks the neck of Canis Major. The star’s name comes from the ancient Greek seirios, meaning “scorcher”. Twice the mass and 25 times more luminous than the Sun, Sirius is a modest star as stars go. It’s not as intrinsically bright as monster stars like Rigel and Betelgeuse. It simply appears bright because it’s the 5th closest star to Earth, only 8.6 light-years away, some 80x closer than Betelgeuse.

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Orion’s Belt points to Canis Major and the bright star Sirius (south is up, east to the right)

The ancient Romans and Greeks associated Sirius with the heat of summer because it rises just before dawn near the summer solstice in the northern hemisphere. According to the poet Virgil, its influence was considered unfortunate, bringing “drought and diseases on sickly mortals”. And it’s the same with the host constellation. In ancient times, the Greeks noted that Canis Major rose before sunrise during the hot, late days of northern summer, during which they noted only a dog would venture into the heat. These “dog days” lent their name first to Sirius, which is sometimes called the Dog Star, and eventually to the entire constellation.

The celestial Big Dog, along with the much smaller constellation Canis Minor, the Little Dog, are often depicted accompanying the great hunter Orion. Canis Minor is marked by the bright star Procyon (“PRO-see-on”) just to the east of Betelgeuse. The ancient Greek poet Aratus, the forgotten poet of stargazers, wrote of Canis Major as Orion’s guard dog. Canis Major was also one of Ptolemy’s original 48 constellations from the 1st and 2nd century A.D., though it was named much earlier.

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Canis Major is populated with mostly young blue stars and star clusters of the Orion Arm of our galaxy. The constellation contains several first and second-magnitude stars which stand out well in this rich section of Milky Way.

As you inspect the constellation, look also for the star Mirzam. Its name means “The Herald”, presumably because it precedes brilliant Sirius as it rises. Although it’s cataloged as β (beta) Canis Majoris, which as you will learn means it should be the 2nd brightest star in the constellation, it is actually the 4th brightest. The star Adhara, or ε (epsilon) Canis Majoris, is the second brightest. It’s also worthy of note. Five million years ago, this star was much closer to the Sun and was, for a time, the brightest star in the sky.

The brightest stars of the constellation Canis Major; the constellations Monoceros to the east of Orion and Lepus and Columba to the south (south is up, east is to the right)

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The Constellations Monoceros, Lepus, and Columba Directly east (or right) of Orion lies the dim constellation Monoceros, which represents a celestial unicorn. It holds no bright stars and is often overlooked for brighter Orion and Taurus and Canis Major. Seeing the outline of a unicorn in this dim patch of stars is nearly as challenging as seeing a real unicorn. If you’re in the city, you’ll find it hard to spot any stars at all.

You might think a constellation that sits near to Orion and takes its name from a unicorn has a long and rich history dating to classical times. But this is not so. Monoceros is a fairly new constellation, and the Greeks had no legends of unicorns. The constellation was first included on a star chart by Petrus Plancius in the early 1600’s, and formalized by Jakob Bartsch in his star charts later in the 17th century.

Look also for the tiny constellation Lepus (“LEE-puss”) just south of the great hunter Orion (above Orion as seen from the southern hemisphere). There are many legends of how Lepus came to be among the stars. The Roman writer Hyginus wrote of a man who brought hares to the island of Leros to raise them for food. A few escaped, and before long the island was overrun with voracious rabbits who consumed crops and caused a famine among the human population. The hares were eventually driven out, but the inhabitants placed Lepus among the stars as a reminder of their experience. The poor celestial hare forever runs from the Big Dog, Canis Major. Perhaps that’s why he’s cowering in the hopes of a little protection at the feet of the great hunter.

Find Lepus by following a line from Sirius through Mirzam (see map above). The small constellation is comprised of an irregular four-sided region of stars with two small stars (legs of the rabbit) off to the left. The two brightest stars, which lie in the four-sided region, are Arneb and Nihal.

South (above) Lepus, look for another small constellation Columba, the Dove, another creation of Petrus Plancius in the early 1600’s. The modestly-bright blue white star Phact is the brightest star in Columba. Contrast it to the slightly fainter orange star Wazn just to the east of Phact.

The Constellation Puppis Further south and east of Sirius and Canis Major lies a rich region of stars high overhead in mid March in the southern hemisphere. Here you see another star, a brilliant yellow-white star called Canopus. After Sirius, Canopus is the second brightest star in the night sky. It is also the brightest star in the constellation Carina. Canopus is cataloged as α (alpha) Carinae.

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Carina was once part of a much larger constellation in this part of the sky called Argo Navis. Most of the stars of Argo Navis were known to ancient Greek astronomers. The constellation was included in the original list of 48 constellations developed by Ptolemy in his Almagest astronomy treatise in the 1st and 2nd century A.D. The constellation represents the massive oar- driven galley in which the legendary Jason and his Argonauts sailed to the Black Sea to find the Golden Fleece. The galley was constructed of sturdy oak beams from trees on Mount Pelion, and the prow of the ship was fitted with a beam from the Oracle of Zeus at Dodona in northern Greece. Argo Navis carried many heroes of Greek legend, including Castor, Polydeuces, and Heracles (or Hercules). After a harrowing passage through the Bosporus Strait which was guarded by the Clashing Rocks that ground other ships to bits, Jason recovered the Golden Fleece from King Aeetes. The expedition ended, and the Argo Navis was beached at Corinth and dedicated to the sea god Poseidon.

The constellation Puppis, south and east of Canis Major

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The constellation Argo Navis was dismantled into the smaller constellations Carina (the “Keel”), Puppis (the “Poop Deck”), Vela (the “Sail”) and tiny Pyxis (the “Compass”) by the French astronomer Nicholas Lacaille in his southern star catalogue of 1762. This part of the sky is rich with bright stars and deep-sky sights for observers south of the equator.

We will examine the constellations Carina and Vela next month. But first to the constellation Puppis (“PUP-iss”). This faint group of stars lies to the southeast of Canis Major, just above the southern horizon as seen from the northern hemisphere. As a constellation, it’s not much to look at, but it does hold a number of fine star clusters worthy of inspection in binoculars or a small telescope.

You have already learned to find Canis Major and Sirius by extending a line from Orion’s Belt upward and rightward to the southeast. You find the faint stars of Puppis by extending this line through Sirius about another 15o. Attempt to trace out the irregular elliptical shape of the constellation. The stars ζ (zeta) and π (pi) are in the middle of the constellation. Also note the position of the stars the rho (ρ) Pup and xi (ξ) Pup located a fist-width east of the star Wezen in Canis Major. This region, and much of the constellation, is a delightful region to slowly sweep across with binoculars because of the rich fields of stars and numerous star clusters located here. You will learn to find a few of the brighter star clusters later this month.

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The path of the constellation Eridanus (note the relatively small size of Orion to the lower right

The Constellation Eridanus Near Rigel, the brighter of Orion’s two feet, begins the long constellation Eridanus (“air-RID-in- us”), the River, which winds from the foot of Orion across a long path of the overhead sky. The constellation has a rich history, and takes its name from the ancient Greek name for the Po River in northern Italy. Eridanus dates back to the 1st and 2nd century A.D., when the astronomer Ptolemy included it in his original list of 48 constellations.

The imaginary river starts near the brilliant star Rigel in Orion and flows away toward the west; then it turns in a southerly direction until it reaches the bright star Gamma (γ), where it bends sharply to the east, and then quickly sweeps off to the south once more and reaches nearly overhead at this time of year as seen from the southern hemisphere. Throughout the whole distance of more than 100 degrees, the course of the stream is marked by rows of stars, and can be recognized without difficulty by the casual observer. Eridanus ends near the bright star called Achernar near the constellation Phoenix. Astronomers have determined that Achernar spins so

Fundamentals of Stargazing -16- rapidly, it is distorted into a somewhat flattened spheroid, with its equatorial diameter more than 50% greater than its polar diameter. It is one of the least spherical stars yet measured.

Have a look at the close pairing of stars just south and west of Rigel. Astronomers cataloged these two stars as ο1 (omicron 1) and ο2 (omicron 2). Omicron-1 is called Beid (“BYED”). Omicron 2, which is the fainter of the two, is also called 40 Eridani or Keid (“KYED”) It’s a binary star, a two-star system, just 16 light years away from Earth. The main component, called 40 Eridani A, is a red dwarf star, just slightly smaller than our Sun. If you’re a big Star Trek fan… you may know that 40 Eridani A is the fictional home star of the planet Vulcan and Mr. Spock. There is not yet any sign of any life in this star system, however, although astronomers have looked!

The portion of Eridanus near the foot of Orion showing the stars Beid and Keid (40 Eridani)

Constellations vs. Asterisms Constellations, of course, are groups of stars organized into patterns that are meant to resemble mythological figures or other types of objects. The stars within each constellation are usually not physically related, and they don’t even lie at the same distance. But they are helpful constructions to help astronomers organize the sky.

Many constellations were invented in ancient times, especially by the ancient Greeks. An early list of 48 constellations was developed by the astronomer Ptolemy in the 1st and 2nd-centuries A.D. as we’ve mentioned. As we’ve seen, his list included the brightest and most prominent constellations like Orion, Taurus, and Canis Major. Other constellations were added much later, in the 16th-18th centuries A.D., to fill patches of sky left blank by Ptolemy.

In 1930, the International Astronomical Union (IAU) formalized a list of 88 constellations that cover the entire sky, including the sky seen from the southern hemisphere. No changes have

Fundamentals of Stargazing -17- been made to this list since it was first developed. All objects on the celestial sphere lie within one of these 88 constellations.

Few amateur astronomers (or even professionals, for that matter) can name all 88 constellations. As a newcomer, you will do well to learn 20-25 of the largest and brightest constellations. In time, you will acquaint yourself with the tiny, dim, and barren constellations that essentially just fill in the gaps of the sky.

Some groups of stars form easily identifiable shapes but are not constellations. The Big Dipper is an example. So is the Little Dipper, and the Summer Triangle, and Orion’s Belt. These groups, which are formed from stars within a single constellation or from several constellations, are called asterisms. You will meet many asterisms as you tour the sky throughout this program...

Fundamentals of Stargazing