The Fundamentals of Stargazing Sky Tours North

01 – The March Sky

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

Head outdoors around 7 p.m. or 8 p.m. on an evening in late February or early March, and turn towards the south. If you can’t find south, 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 southward before you can proceed. You will also need a good view of the sky in the south, so you may need to get away from structures and trees and so on.

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

Now that you’re facing south with a good view of a clear sky, look for bright stars. There are quite a few in this part of the sky. You are looking, in particular, for the tell-tale shape of the constellation Orion, which you can see in the map below. Orion depicts a hunter standing upright, as seen from the northern hemisphere, adorned with a belt and sword, and holding a westward facing shield in his left hand and an upraised club in his right.

Note: The maps in this tour are accurate for 45 degrees north latitude. If you live north of this latitude, Orion will appear slightly closer to the horizon. If you live south of this latitude, the stars appear further above the horizon.

Most observers recognize Orion by the three bright stars of his belt. These stars line up on a slight diagonal as seen from most parts of the northern hemisphere, and span about the same width as your three largest fingers held together at arm’s length. Well above the belt lie two brighter stars. The brighter left star is clearly orange-red. This is the star Betelgeuse (“BAY- tell-jewz”). It marks one of the shoulders of Orion. The right star is whitish-blue and goes by the name of Bellatrix.

Below the belt lie two more bright stars marking Orion’s feet. The brilliant blue left (or westward) star 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.

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

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 Orion’s feet, 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 left to right) 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 above) the shoulders of Orion, look for the small patch of fainter stars that mark the hunter’s relatively faint 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 hang off the belt. 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 Nebula where a cluster of brand-new stars are in

Fundamentals of Stargazing -5- 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.

The Constellation Taurus Using Orion as a base of operations, you can now navigate to other prominent constellations. Extend a line from Orion’s Belt toward the northwest (the upper right as seen from the northern hemisphere in the early evening hours in late winter). You will arrive at a bright orange star. 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 one of the loveliest constellations of the northern winter sky. 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 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

Fundamentals of Stargazing -6- eye. Extend each arm of the “V” of Taurus to find the tips of the horns marked by the stars zeta Tauri and beta Tauri, sometimes called Elnath or Alnath.

Orion’s Belt points the way to the constellation Taurus

The Pleiades 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.

You will examine the Hyades and Pleiades star clusters in more detail shortly this month. But first, let’s follow the horns of the celestial bull to Auriga, another prominent constellation.

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The constellation Taurus and the Pleiades

The Constellation Auriga Now to the constellation Auriga (“or-EYE-gah”). This large hexagonal constellation lies directly north of Orion and is marked by its brightest star, the yellow-white Capella which lies high overhead on an early evening in February and March about two full hand lengths above Rigel.

The Greeks had a number of legends associated with this ancient constellation, but they all involve some form of charioteer, likely because the peaked shape of the constellation resembles the rider’s helmet. The conventional legend has Auriga representing Erichthonius, a king of Athens who was raised by Athena and invented the quadriga, a four-horse chariot.

The Babylonians also related this star group to a chariot. So did the Chinese, who saw the stars Capella (alpha), beta, theta, and iota Aurigae along with Alnath, also called β (beta) Tauri,

Fundamentals of Stargazing -8- representing the chariots of five celestial emperors. The stars epsilon (ε), zeta (ζ), and eta (η) Aurigae are tethering poles for the horses.

Auriga looks like a large hexagon spread over some 15º of sky. The brightest star, Capella, is a dazzling yellow-white giant star and one of the three brightest in the northern hemisphere. Capella contrasts nicely with the blue-white Menkalinan (“men-KAH-li-nan”). The stars theta, iota, and zeta complete the hexagon, along with Alnath, which actually belongs to the constellation Taurus. Alnath (blue) and ι (iota) Aur (orange) also contrast nicely.

The constellation Auriga

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Capella, which is an intriguing quadruple star system, takes its name from the Latin for “little she-goat” carried by the charioteer on his shoulder, presumably. The triangular grouping of stars epsilon (ε), zeta (ζ), and eta (η) Aurigae are often called “The Kids”. The Kids and Capella fit into the same field of view in most binoculars, and they are a lovely sight. Though you can’t tell simply by looking, you are seeing stars here of very different distances. Capella is just 40 light years away, eta is 220 light years, zeta is 850 light years, and epsilon is some 2,000 light years away. Epsilon is an extremely bright star (intrinsically), and it has a strange companion star shrouded in dark dust that eclipses the main star every 27 years. The last eclipse occurred in 2011.

If you have binoculars, look at the region between iota Aurigae and Alnath. It is particularly fine, with a spray of hundreds of faint stars visible in dark sky.

Note: If you’re getting a little confused about all these Greek letters for star names, fear not. I will explain how they work as the course goes by. For now, just remember what you can about the names and shapes of these strange letters and find a few of them on the star maps as you learn your way around the sky.

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, 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.

Because it lies low in the sky as seen from the northern hemisphere, Sirius often twinkles aggressively. This is an effect caused by the thick atmosphere near the horizon, which momentarily bends the star’s light causing an apparent movement and color change. As you look at Sirius over a number of evenings, watch this normally blue star appear to flash white, yellow, green, and even red.

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Orion’s Belt points the way to Canis Major and the bright star Sirius

Although many think of Sirius as a winter star, the ancient Romans and Greeks associated Sirius with the heat of summer because it rises just before dawn near the summer solstice. 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. Ancient Greek poet Aratus, the forgotten poet of stargazers, wrote of Canis Major as Orion’s guard dog. Canis Major was also

Fundamentals of Stargazing -11- one of Ptolemy’s original 48 constellations from the 1st and 2nd century A.D., though it was named much earlier.

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 the 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, which is the second-brightest star of Canis Major is 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 constellation Monoceros (North is up, west is to the right)

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The Constellations Monoceros and Lepus Directly east (or left) 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. 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.

The Constellation Eridanus Near Rigel at Orion’s left foot begins the long constellation Eridanus (“air-RID-in-us”), the River, which winds from the foot of Orion into the deep southern sky below the horizon. 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.

Eridanus begins near the star Cursa, just west of Rigel, in Orion, and moves straight west, cuts back east, then drops directly south. Only stargazers in the southern hemisphere can see all of it, including the bright star Achernar at the end of this celestial river. The constellation lies nearly overhead for observers in the southern hemisphere.

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.

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Spock. There is not yet any sign of any life in this star system, however, although astronomers have looked!

The constellations Lepus, the Hare, and Eridanus, the River to the south and west of Orion

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 seen, his list included the brightest and most prominent constellations like Orion, Taurus, and Auriga. Other constellations were added much later, in the 16th-18th centuries A.D., to fill patches of sky left blank by Ptolemy.

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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 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