Thursday, December 25, 2008

Ringing in the New

For a sky-watcher, ringing in the New Year can best be accomplished by gazing rapturously at the rings of Saturn. This year, however, as we say goodbye to 2008 and hello to 2009, we can gleefully gawk at the absence of rings.

Planet Saturn is tilted in relation to its orbital path around the Sun. As it chugs around the Sun— in an orbit that lasts 30 Earth years— sometimes its rings are tilted open from our vantage point, showing us either the “top” surface of the rings or the “bottom.” And twice during its orbit, that is, every 15 years, we experience a ring plane crossing, when our view of Saturn is side-on or edge-on, and the remarkably thin rings disappear from view.

The next ring plane crossing is coming up quickly and will occur in September of 2009. Because of this, the rings have been gradually closing from our perspective. By the end of this month, they’ll be less than one degree open. Imagine an angle measuring one degree: that’s really small! Since Saturn will be quite close to the Sun in September and therefore not well placed for us to view the vanishing of the rings, this is an excellent time to sneak a peek. After all, what’s one silly little degree among friends?

Grab your telescope, beg or borrow a telescope, or look for telescope observing opportunities through your local observatory, planetarium, science museum, or astronomy club. This is no time to be shy!

1) To spot Saturn, you’ll need to face east. If you don’t know the cardinal directions at your location and you don’t have a compass, make note of where the sun sets on the horizon. That spot is approximately west. Stand with your back to the west, and you’ll be facing approximately east.

Star map created with Your Sky

2) About an hour or so before midnight, Saturn will rise over the eastern horizon, behind Regulus, the bright star that marks the Lion’s Heart in the constellation Leo. You may also recognize Regulus as the star marking the bottom of the asterism that looks like a backwards question mark, the one called the Sickle. An asterism is a recognizable star pattern. Saturn will be brighter than Regulus, and it will have a golden color.

3) The later in the evening you can wait to observe Saturn, the better. The higher Saturn is in the sky, the less atmosphere you’ll be looking through. Generally speaking, this translates to a clearer, steadier image in your eyepiece.

4) Once you have the golden planet in view, you’ll notice the nearly edge-on rings. When I observed Saturn recently, this is what I saw:

It was quite startling to see no ring plane surface. Rather, there was the effect of a straight line, white on the ends outside the planet’s disc and black where it crossed the disc. The black line is the shadow of the rings cast onto the surface of the planet by sunlight.

5) What I also observed, which you can see quite readily, was Saturn’s slightly squashed shape. Because the planet is a rapidly spinning sphere of gasses, it has developed an equatorial bulge, that is, it bulges along its equator. Having just indulged in Christmas dinner, I can certainly relate.

With the incredibly bright rings out of the way and a sideways view, now we can enjoy what is often overlooked: the oval shape that resembles a sat-upon beach ball.

6) To finish up your communion with the ringed one, look for the usual sprinkling of moons just beyond the edges of the rings They’ll look like little stars, and it’s a fun challenge to see how many you can spy.

See you next year!

Credit: NASA/JPL

Thursday, December 18, 2008

A Lizard's Tale

The minor constellations are often overlooked because their stars tend to be dim and are best spotted in dark skies relatively free of light pollution. For a change of pace, it can be fun to stalk these secretive creatures when you’re away from city lights.

This is a good time of year to search the crevices of the sky for Lacerta the Lizard (luh-SIRR-tuh). Although at various times and places its unassuming star pattern was seen as a newt, a weasel, a winged serpent, and a scepter, the Lizard designation finally took hold.

The small, reptilian constellation was established in 1690 by Johannes Hevelius, a Polish astronomer and star atlas maker. It is, therefore, considered a modern constellation, rather than one of the classical constellations, which have roots in ancient cultures and are usually associated with myths and legends.

Lacerta in Bode’s 1801 star atlas
Courtesy of
Linda Hall Library of Science, Engineering and Technology

Lacerta is one of the ten smallest constellations of the Northern Hemisphere sky and fairly dim. Let’s dark adapt and see if we can tease our wriggly friend into view.

1) Face south. If you don’t know the cardinal directions at your location and you don’t have a compass, make note of where the sun sets on the horizon. That spot is approximately west. Stand with your right shoulder to the west, and you’ll be facing approximately south.

2) About an hour after sunset you should be able to spot the Great Square of Pegasus nearly overhead or, if you’re observing from a far north latitude, about a quarter of the way from the zenith (the spot directly overhead) down toward the southern horizon.

Star maps created with Your Sky

3) If you draw an imaginary line between the center of the Great Square and Deneb, the brightest star in Cygnus the Swan, you’ll cross the tip of the lizard’s tail. His body extends up towards the House of Cepheus the King.

4) Because of Lacerta’s modern origin, it has no stars with traditional names. The brightest star, which we call Alpha for its star catalog designation, is a white dwarf star.

How many of the lizard’s six zigzagging segments can you spot?

Thursday, December 11, 2008

Biggest Moon, Smallest See

This week, for your observing pleasure, I give you the biggest Moon to moon over and the smallest sea to see.

Just after sunset on Friday, December 12, look east to watch the Full Moon rising. This month, the Full Moon occurs only a few hours after it reaches perigee, which makes it the biggest Moon of the year. Perigee is the point in the Moon’s orbit where it’s closest to Earth. The Moon’s orbit is an oval-shaped ellipse, not a circle. At one narrow end of its elliptical orbit, the Moon is at perigee. At the other end, it’s at apogee, the point in its orbit where it’s farthest from Earth.

Image source: NASA

As with any object, the closer the Moon is to us, the larger it appears. In particular, Friday’s Full Moon will appear about 14% bigger and 30% brighter than it did when it was near apogee, back in June. Of course, you won’t have the apogee Moon hanging in the sky next to the perigee Moon to aid you in size comparison. You’ll just have to take my word for it and enjoy the show as the super-sized Moon climbs in the sky.

Appearance of Moon at perigee and apogee in 2007

Take advantage of the jumbo Moon to look for the smallest naked-eye lunar feature that most people can see: the Sea of Crises or Mare Crisium (MAH-ray CRISS-ee-yum). A mare (MAH-ray) is a crater that filled with lava that afterwards cooled and solidified into basalt. Although Mare Crisium is not the smallest sea on the Moon, it is a mere 260 miles in diameter. Spotting it is quite an accomplishment.

Image from Wikipedia

Look for Mare Crisium soon after moonrise on the 12th, while the sky is still bright with twilight. I don’t have the sharpest eyesight, and I find it easiest to pick out that feature when the Full Moon is not yet blindingly bright, as it will certainly become after twilight fades and the sky darkens. Mare Crisium will be near the upper limb of the rising Moon; the limb is the outer edge of the Moon’s disc. Look for a small, dark dot just above the “ears” of the Rabbit in the Moon.

If you can’t look on Friday evening, watch for the moonrise on Saturday evening, about an hour after sunset, and try it then. After Saturday, you won’t be able to spot Mare Crisium, as that edge of the waning (shrinking) Moon will be in shadow. You’ll have to wait until a couple days after the next New Moon on December 27 to try to spot the little sea in the first illuminated slice of the waxing (growing) crescent Moon.

If you observe the biggest Moon and/or if you spot Mare Crisium, post a comment on this page and share your success!

Thursday, December 4, 2008

The Way

There are an estimated 100 billion galaxies in the universe, and we occupy just one of them, the Milky Way.

It was the great 20th century American astronomer Edwin Hubble who determined that many mysterious telescopic objects thought to be emerging solar systems were in fact galaxies— immense star systems lying beyond the Milky Way. The Milky Way was not, it seemed, the whole enchilada. This discovery expanded our cosmic horizons and gave us our first inkling of just how immense the universe was.

Since Hubble’s landmark discovery, we’ve learned quite a bit about our cosmic 'hood. We now know that the Milky Way is a barred spiral type of galaxy. A spiral galaxy is shaped somewhat like a pinwheel, with curved arms radiating out from a center that is densely packed with stars. In a barred spiral, the center has an elongated shape.

We also know that there’s a supermassive black hole lurking at our galaxy's center. A black hole is an object so dense that nothing— not even light— can escape from its gravitational field.

Courtesy NASA/JPL-Caltech

In addition, we’ve learned that the Milky Way contains around 400 billion stars. We know it’s around 200,000 light years in diameter; one light year is the distance light travels in one Earth year, nearly six trillion miles. Knowing these numbers doesn’t necessarily mean we mere mortals can fully grasp the size and distance involved. The implication for a short-lived species such as Homo sapiens is that space travel to other parts of our galaxy would require thousands of successive generations of people on each pioneering space ship.

However, like all the generations of our species that came before us, we can see the Milky Way on most any night. If we look skyward from a dark site away from urban light pollution, we can enjoy an edge-on view of the star-packed arms of our platter-shaped galaxy. Because the Milky Way is a horde of stars too numerous and faint to be resolved (separated into distinct points of light) with the naked eye, we see it as a hazy band of light arching across the sky. Some folks seeing the Milky Way for the first time mistake it for a long, lingering cloud.

The poetic name for our home galaxy comes to us from the Latin Via Lactea (Milky Way), which in turn derived from the Greek word for milk. A number of other cultures also saw the band of light as a stream of milk. But around the world, there have been numerous names given to this distinctive celestial object. Here are just a few:

- Silver River
- Winter Street
- Path of White Ashes
- Birds’ Way
- Straw Road
- Pilgrims’ Road
- Great Serpent
- River of Heaven
- Heavenly Girdle
- Road of Souls
and my personal favorite, from the Polynesians:
- Long Blue Cloud-Eating Shark

My pet name for the Milky Way is simply “the Way,” because it represents for me a way of being and a way of seeing. I learned an important lesson a number of years ago on a camping and observing trip in southern Arizona. I had spent the better part of a night glued to the eyepiece of my telescope, hunting various galaxies, globular clusters, and nebulas on an observing list and methodically ticking off those “faint fuzzies” as I found them. Straightening up from the eyepiece to stretch my back, I faced south and audibly gasped. The woods south of the clearing where I and my partner were observing were on fire!

After a few heart-pounding seconds, I noticed that the raging firestorm licking the sky above the trees was black-and-white. Black-and-white flames? Then it dawned on me that what I thought was a forest fire was the Summer Milky Way, which had risen in all its magnificence while I was attached like a barnacle to my telescope.

Because I am fortunate to live and observe in New Mexico, which has excellent observing conditions, I thought I had seen the Milky Way. But I had never seen it like I saw it that night. The combination of superb transparency (atmospheric clarity) and a deep, dark, black-as-the-ace-of-spades sky background made every tendril and wisp of the Way pop out in blazing, 3D relief.

I almost missed the finest view of the night, a deeply satisfying naked-eye spectacle that flickered across my retinas and seared itself into my memory. And here’s the strange lesson: sometimes even serious sky observers have to remember to just look up.

Thursday, November 27, 2008

Giving Thanks

These are a few of my favorite things.

Dance of the Planets
Watching the naked-eye planets (Mercury, Venus, Mars, Jupiter, Saturn) rhythmically huddle and disperse is like watching an intricate dance. These planetary alignments are the result of our earthbound view of the naked-eye planets moving in their respective orbits around the Sun. Some are traveling faster than Earth; some are traveling slower. The resulting variety of configurations gives us a sense of the “clockwork of the universe” and reminds us that everything is in motion.

Solar system diagram created with Solar System Live

Be sure to look southwest after sunset on Monday, December 1, when Venus, Jupiter, and the crescent Moon will bunch up in the twilit sky. Venus will be the brighter of the two star-like objects you see, and Jupiter the fainter. The waxing (growing) crescent Moon will be about 15 percent illuminated.

While you're enjoying the alignment, look for earthshine on the Moon. Earthshine is sunlight reflecting off the surface of the Earth and illuminating the dark part of the Moon. Even though the bright crescent is the only part of the Moon’s face being directly illuminated by the Sun, if you look carefully, you’ll see that the rest of the Moon’s face is glowing faintly with reflected glory: earthshine.

Shooting Stars
Wishing on a “falling star” is one of the guilty pleasures of the stargazer. Even after you know that falling stars, aka "shooting stars," are meteors, you can still appreciate this charming holdover from early folkloric traditions.

A meteor is the streak of light we see in the sky when a bit of dust or space debris hits Earth’s atmosphere at high velocity. A meteor shower occurs when Earth encounters a stream of debris left behind by a comet’s close approach to the Sun. Sporadics are meteors not associated with a particular shower.

Meteor showers occur reliably around the same time every year, as Earth returns to the point in its orbit where the debris field lies. Whenever you like, you can find out what meteor showers are currently active by visiting this website and scrolling down to the Meteor Shower Calendar.

Meteor storm - 1889 engraving by Adolf Vollmy

If you’re lucky, you might someday see a meteor storm, a very intense meteor shower with a high frequency of meteors. One of my top ten stargazing experiences ever was viewing the 2001 Leonid meteor storm. The meteors came so fast and furious, it was a bit like watching a fireworks show. I was with a large group of fellow amateur astronomers at a dark-sky site, and the oohs and aahs from the crowd as particularly fine meteors blazed across the sky just added to the ambiance of the event. We all knew we were seeing something rather spectacular.

Cosmic Dust Bunnies
Interplanetary space is not empty. Our solar system contains a vast number of minute particles, some left over from the time of planet formation and some ejected from passing comets or asteroid collisions. Light from our Sun illuminates the myriad particles lying in the solar system plane, and sometimes we see the reflected sunlight as a luminous pillar of light called the zodiacal light.

The zodiacal light (zoh-DYE-uh-kull) is a large, roughly triangular or cone-shaped glow in the night sky, extending upwards from either the eastern or western horizon. The base of the triangle or cone— the widest part of the glow— is at the horizon. The zodiacal light is typically seen in the spring above the western horizon after sunset and in autumn above the eastern horizon before sunrise.

If you're fortunate enough to view the zodiacal light when transparency (atmospheric clarity) is good and the sky is inky black, you may notice the light pillar has a yellowish cast. Our Sun is, after all, a yellow star, so it shines with a golden light.

Cone-shaped glow of zodiacal light above sunset glow
Image source: ESO

The zodiacal light is subtle and can be quite challenging for the beginner to spot. A dark site away from urban and suburban night lighting is critical for success, as is avoidance of a moonlit night.

Believe me, this phenomena is worth a little extra effort. It’s quite a rush when you spot it, especially when you then start thinking about what you’re looking at— vintage dust from when the solar system formed. The goofy image that always pops into my head is the Sun as a clean freak with a big flashlight, showing us what lurks under the furniture.

The Way
My personal pet name for our home galaxy, the Milky Way, is simply “the Way,” because it represents for me a way of being and a way of seeing. I learned an important lesson a number of years ago on a camping and observing trip in southern Arizona. I had spent the better part of a night looking through the eyepiece of my telescope, hunting various galaxies, globular clusters, and nebulas on an observing list and methodically ticking off those “faint fuzzies” as I found them. Straightening up from the eyepiece to stretch my back, I faced south and audibly gasped. The woods south of the clearing where I and my partner were observing were on fire!

To be continued…

Thursday, November 20, 2008

The Reclusive Ram

Aries the Ram is a bit of a recluse, hiding in plain sight in the late autumn sky. Although not terribly impressive to behold, Aries is historically an important constellation. In the astrological zodiacs of numerous ancient civilizations, it was considered the first zodiacal constellation, or first sign. This designation may have been made when it was noted by the ancients that the Sun was positioned in Aries at the spring equinox.

The spring equinox is the moment when the center of the Sun is directly above the Earth’s equator. This occurs only twice a year; the other occurrence is known as the fall equinox. Another name sometimes given for the spring equinox is first point of Aries, which, of course, derives from old astrological traditions.

Aries in Bayer's 1603 star atlas
Courtesy of Linda Hall Library of Science, Engineering and Technology

The “first sign” tradition continues today; Aries is usually listed first in horoscope columns found in newspapers and magazines. You’ll also note that the conventional date range given by astrologers for people “born in the sign of Aries” begins on March 21; spring equinox typically occurs on or near March 20.

By the way, the Sun is no longer in Aries at the spring equinox. Due to precession— sometimes called precession of the equinoxes— which is the wobbling-top motion of Earth’s axis, the equinoxes occur a few minutes earlier each year. As a result, at each spring equinox, the Sun is not in the same position it was the previous year against the background stars, as seen from Earth. If we track the Sun’s position over the years at a fixed point in time (such as the spring equinox), from our perspective on Earth the Sun would appear to move through all 12 zodiacal constellations in reverse. As a result of precession, the Sun is now in Pisces, the twelfth zodiacal constellation, at the spring equinox.

Aries in Middleton's 1842 star atlas
Courtesy of
Linda Hall Library of Science, Engineering and Technology

In mythology, Aries represents the ram whose golden fleece was famously sought by Jason and the Argonauts. Let’s conduct our own search for the storied sheep.

1) Wait about two hours after sunset to begin observing, so that Aries is high enough in the sky.

2) Face east. If you don’t know the cardinal directions at your location and you don’t have a compass, make note of where the sun sets on the horizon. That spot is approximately west. Stand with your back to the west, and you’ll be facing approximately east.

Star maps created with Your Sky

3) Find the Great Square of Pegasus, which is nearly overhead, and the Pleiades star cluster, which is low in the east. These are both easy to spot using the star map above. Midway between them is Aries. Look for a small, curved line of three stars. This is the most notable asterism (recognizable star pattern) in Aries. It always remind me of a comma, so I call this asterism the Comma. Unfortunately, there’s nothing in the scattering of stars in Aries that particularly resembles a ram, unless you want to think of the Comma as a curving ram’s horn.

4) The brightest star in Aries is Hamal (hah-MAHL), which comes from the Arabic for lamb. Other ancient names for this star had meanings like ram’s eye, horn star, and leading one (the ram that led the celestial flock). Hamal is an orange giant star, 66 light years away. One light year is the distance light travels in one Earth year, nearly six trillion miles.

5) The second brightest star in Aries is Sheratan (SHER-uh-tunn), from the Arabic for the pair, a reference to Sheratan and the final star in the Comma, which we’ll look at next. Sheratan is a white star. When you compare it to Hamal, can you see that orange giant Hamal has a more golden hue?

6) Mesarthim (mess-ahr-TEEM) is from the Hebrew for servants. Mesarthim, a white star, may only be Aries’ fourth brightest but it’s known as the first star of Aries. This is because in antiquity, when the spring equinox was in Aries, Mesarthim was the closest Ram star to the equinox. Physically, the equinox can be described as the intersection of the Sun’s path with the celestial equator, the imaginary line that represents the Earth’s equator extended out into space.

7) Although the third brightest star in Aries has no traditional name and is instead saddled with the uninspired moniker Flamsteed 41, it does manage to be part of a funky little asterism. The blue-white dwarf star is the brightest member of a four-star asterism known as the Northern Fly, riding on the ram’s back. To find Flamsteed 41 and the Northern Fly, look northeast of Hamal and east of the constellation Triangulum.

In its glory days, this asterism was part of a now-defunct constellation by the same name, which was introduced in the 17th century. Now it’s merely a curiosity for naked-eye stargazers like us and, I imagine, a constant irritant for our celestial ram.

The Ram and the Fly in Bode's 1801 star atlas
Courtesy of
Linda Hall Library of Science, Engineering and Technology

Thursday, November 13, 2008

The Cockeyed Moon & the Listing Earth: Part I

Question posed by a reader: I’ve noticed that the Moon doesn’t always rise in the same spot on the horizon. Is there a pattern to this over the course of a month and over the course of a year?

Answer: Yes!

You could say that our Moon marches to the beat of a different drum. Any self-respecting natural satellite would orbit directly above its planet’s equator, ensuring no change from day to day in the position of the moonrise on the eastern horizon. Not so with our cockeyed Moon.

Instead, the Moon’s path as it orbits Earth is much more closely aligned with the ecliptic, the imaginary line that represents the path the Sun appears to take across the sky, as seen from Earth.

The Cockeyed Moon
Image source: NASA

Hopefully, you’ve noticed that the Sun rises at different spots on the eastern horizon over the course of a year. It rises incrementally farther to the north as we approach the summer solstice in June. Then it reverses course, rising incrementally farther to the south as we approach the winter solstice in December. This occurs because Earth lists a bit. That’s right, our home planet is permanently tilted with respect to its orbit around the Sun. In other words, the Sun is not above the Earth’s equator all the time. If it were, we would see no change in the position of each sunrise.

The Listing Earth
Image courtesy of Tau’olunga

Because it roughly follows the path of the ecliptic, the Moon has a rise cycle with a northern and a southern extreme, just like the Sun does. The Moon, however, goes through its cycle in one month, not one year. In any given lunar month, the moonrise travels back and forth between an extreme northeast position on the horizon and an extreme southeast position. This is observable. Check it out!

First, find a location with a clear view of the eastern horizon. You’ll need to use this same location on several dates over the course of one lunar month. A lunar month or lunar phase cycle is the time it takes the Moon to orbit the Earth and reach the phase it started from, as seen from Earth (for example, Full Moon to Full Moon or 8% waxing crescent to 8% waxing crescent). The average length of a lunar month is 29.5 days.

Second, decide how you will mark moonrise positions on the horizon. If you have a horizon with a lot of topographical and/or manmade landmarks, you could simply make notes describing where the Moon rose with reference to specific landmarks. You may want to sketch the horizon and its landmarks and mark the different moonrise positions and their dates on your sketch. You may even decide to capture the moonrises photographically. It’s up to you.

Third, use the named phases of the Moon (New Moon, First Quarter, Full Moon, Third Quarter) to streamline your data capture. The dates of these phases for any given month can be found on most calendars. If you simply record the moonrise position on the dates of five consecutive named moon phases, you’ll have what you need. A First Quarter Moon rises a couple hours before or after 12 noon, Full Moon rises around sunset, and a Third Quarter Moon rises around midnight or later. Check this website for moonrise times in your area.

Phases of the Moon
Image source: NASA StarChild

New Moon is a bit tricky. Because the Moon travels so close to the Sun in the daytime sky at New Moon, you won’t be able to observe the moonrise at New Moon. However, you can note the approximate location of sunrise on the eastern horizon at New Moon and use that for your moonrise position. It’ll be very close to the Moon’s actual position. (WARNING: Never look directly at the Sun, as this will permanently damage your eyes!)

When you complete this project, your five position markers will show you that the moonrise does indeed swing back and forth between a northeast and a southeast extreme (not necessarily in that order).

We’ll revisit this topic at a later date in Part Two, when we’ll take a look at moonrise positions and the pattern that emerges over the course of a year.

Thursday, October 30, 2008

Haunted Sky

It is with ghoulish pleasure that I present you with 13 spine-tingling Halloween treats— of a celestial nature. There’s something here for everyone: naked-eye stargazers, telescope observers, and armchair astronomers who just want their eyeballs exquisitely tortured with devilishly detailed astronomical imagery.

Keep reading, but only if you’re brave enough to whistle in a stellar graveyard.

1) The Coffin (naked eye)
Hanging just above the western horizon after sunset— and northwest of bright Jupiter— is the summer constellation Ophiuchus (oh-fee-YOU-kuss) the Serpent Handler. A number of the brightest stars in this constellation form the asterism (recognizable star pattern) called the Coffin, which looks like an old-fashioned casket with a pointed head.

Star maps created with Your Sky

2) Little Ghost Nebula NGC6369 (armchair)
This faint planetary nebula in Ophiuchus currently trails just behind Venus. A planetary nebula is a dying star, that is, it’s the stellar material (gas and dust) being puffed off during a moderate-sized star’s death throes.

Normally, a medium- to large-aperture (diameter) telescope is required to view the Little Ghost. However, it’s currently too low in the west after dark to get a good view. Find bright Venus in the western sky at sunset, and imagine the Little Ghost floating right behind her. Then just stare zombie-like at this beguiling image taken by the Hubble Space Telescope.

Little Ghost Nebula
Source: NASA and The Hubble Heritage Team (STScI/AURA)

3) Snake Nebula B72 (armchair)
This tortuous dark nebula in Ophiuchus is just west of the Little Ghost. A dark nebula is a dense interstellar cloud that obscures light from the stars behind it. To the observer, it looks deceivingly like a void in space. In this case, the Snake is obscuring the rich star fields of the Summer Milky Way.

Although the Snake Nebula can be viewed telescopically, it’s currently too low in the west after dark to be visible. Your consolation prize is this image that practically hisses.

Snake Nebula
Source: Tom McQuillan/Adam Block/NOAO/AURA/NSF

4) Ghost of a Cheerio M57 (telescope)
This alternate name for the Ring Nebula perfectly describes the planetary nebula’s spectral, smoke ring appearance. It can be viewed satisfactorily in even a small telescope. However, you’ll need substantial aperture, a dark sky, and a good eye to spot the faint central star that’s dying and throwing off all the ghostly material.

Look for M57 in Lyra the Harp, south of the Summer Triangle star Vega.

5) Job’s Coffin (naked eye)
High overhead in the little constellation Delphinus (dell-FINE-uss) the Dolphin is the asterism known as Job’s Coffin, a quadrilateral of four stars. Look for the Dolphin sandwiched between two geometrical shapes: east of the Summer Triangle and west of the Great Square of Pegasus.

6) Cocoon Nebula IC5146 (armchair)
North of the Dolphin in the constellation Cygnus the Swan, near the bright Summer Triangle star Deneb, is the mysterious Cocoon Nebula. This large diffuse nebula is a stellar nursery, a cloud of gas and dust where new stars are forming. Because of its low surface brightness, it’s a very challenging object to observe and is perhaps best left to the seasoned observers with large-aperture telescopes. As for the rest of us, let’s ponder what else might be hatching in that cocoon while we examine this image taken at Kitt Peak Observatory.

Cocoon Nebula
Source: Julie and Jessica Garcia/Adam Block/NOAO/AURA/NSF

7) Demon Star (naked eye)
Face north. Rising in the northeast is the constellation Perseus the Hero, which contains the notorious variable star Algol, aka the Demon Star or the Ghoul Star. Algol is a double star, and its orbiting companion star eclipses it like clockwork every 2.8 days. This makes Algol’s brightness dip suddenly and dramatically. Perhaps this eerie effect is what led the ancient Greeks to consider Algol the decapitated head of Medusa, being brandished by her slayer, Perseus. Medusa was the snake-haired creature whose frightful appearance turned anyone who looked upon her to stone. Look for Perseus just northeast of the Lazy W asterism of Cassiopeia.

8) Cat’s Eye Nebula NGC6543 (telescope)
Still facing north, you’ll find the Cat’s Eye, another planetary nebula, just northeast of the Lozenge, the asterism that marks the head of the constellation Draco the Dragon. The Cat’s Eye is a telescopic heart-thumper due to its spellbinding aqua color. Once you find the “eye,” imagine the cosmic black cat it might belong to.

9) Skull Nebula NGC246 (telescope)
Just north of Diphda (DIFF-duh), the brightest star in the constellation Cetus the Whale, is the planetary nebula known as the Skull. Here’s a Halloween trick: if your scope doesn’t pull in enough of the nebulosity to give you the skull effect, focus on the triangle of three bright stars that could be two glowing eyes and a nose. With the surrounding wisps of nebulosity giving shape to a head, the object becomes the face of a wolf. Or perhaps a werewolf?

Nebula as skull

Nebula as wolf

10) Witch Head Nebula IC 2118 (armchair)
The Witch Head is technically in the constellation Eridanus the River, however, it’s easier to think of it located just to the right of Rigel, the brightest star in the constellation Orion and the one that marks the Hunter’s left foot. In fact, light from supergiant Rigel is what’s illuminating the nebula’s dust particles and making them glow. You’ll find Orion the Hunter well up over the eastern horizon before midnight.

This diffuse nebula is immense and faint. Like the Cocoon Nebula (#6), this one’s not for the faint of heart or the small of aperture. Best we keep our distance from the gnarly-faced witch and simply gaze at her profile in this image by astrophotographer John Sefick.

Witch Head Nebula

11) The Sickle (naked eye)
A couple hours after midnight, this stand-out asterism in the constellation Leo the Lion will have risen above the eastern horizon. The Sickle looks like both a backwards question mark and the farming implement traditionally brandished by the Grim Reaper.

12) Ghost of Jupiter NGC3242 (telescope)
The bottom of the Sickle points toward this planetary nebula in the constellation Hydra the Water Snake. It should be viewable in most telescopes and will appear as a dim bluish orb. It was nicknamed the Ghost of Jupiter because, in a telescope, it has about the same apparent size as the planet. Apparent size is the amount of sky an object covers from our perspective on Earth.

Ghost of Jupiter

13) Tarantula Nebula 30 Doradus (armchair)
This Southern Hemisphere object isn’t visible to us Northerners, and it’s not even in the Milky Way, but it’s simply too creepy not to include. It’s actually a gargantuan star-forming nebula in the Large Magellanic Cloud, a small satellite galaxy of the Milky Way. However, its fuzzy “spider legs” of gas and dust make it the perfect Number 13 for this list.

Have a boo-dacious Halloween.

Tarantula Nebula

Thursday, October 23, 2008

Lady in Chains

The constellation of Andromeda the Chained Woman is one of the premiere sights of the autumn sky. In Greek mythology, Andromeda (ann-DROMM-eh-duh) was the daughter of King Cepheus (SEE-fee-yuss) and Queen Cassiopeia (kass-ee-oh-PEE-yuh). Because the insufferably vain Cassiopeia offended the gods, Andromeda was chained to a rock by the sea as an offering to the sea monster Cetus (SEE-tuss).

The Royal Family: Cepheus, Cassiopeia, Andromeda & Perseus
Star maps created with
Your Sky

Cassiopeia the Queen, Cepheus the King, Andromeda, and Andromeda’s rescuer and subsequent husband, Perseus the Hero, are all immortalized in the night sky as constellations. The four star groups are known collectively as the Royal Family. They can be observed together in the night sky after sunset, in fall and winter. Also lurking nearby, through early winter, is the constellation Cetus the Sea Monster, aka Cetus the Whale.

Let’s take a closer look at the stars of our damsel in distress.

1) Wait at least one hour after sunset to begin observing, so that twilight’s faded and your sky’s good and dark.

2) Since we’re approaching New Moon on October 28th, you’ll have plenty of dark hours to observe before the Moon rises.

3) Face east. If you don’t know the cardinal directions at your location and you don’t have a compass, make note of where the sun sets on the horizon. That spot is approximately west. Stand with your back to the west, and you’ll be facing approximately east.

4) First find the Great Square of Pegasus, about halfway between the zenith (the point in the sky directly above your head) and the eastern horizon. The Great Square is an asterism, a recognizable star pattern, within the constellation Pegasus. It's defined by four bright stars, one at each corner. Each side of the Square is about one and a half to two fists wide, if you hold your fist at arm’s length against the sky and measure across the widest part.

5) From the corner star that is farthest north, look for two chains of stars curving north. Not counting the corner star, there are three bright stars in each chain.

6) The corner star, although part of the Great Square asterism, is technically in Andromeda. Its name, Alpheratz (AL-fuh-rats) sounds like a lab experiment gone terribly wrong, but it’s Arabic for horse’s shoulder, a reference to Pegasus.

Along the lower chain— the one closest to the eastern horizon— the star to the left of Alpheratz has no traditional name, so we call it Delta, its star catalog designation. Next in line is Mirach (MIRR-ahk), Arabic for girdle. Mirach and Alpheratz are tied for the title of brightest star in Andromeda. Mirach is a red giant; compare it visually to blue Alpheratz. Can you see the difference in hue?

Last in line on the lower chain is Almach (ALL-mahk). Almach is from the Arabic for caracal, a nocturnal cat found in Africa and Asia.

7) Let’s jump to the upper chain, again starting at Alpheratz and moving left. All three stars of the upper chain have no traditional names, so we use their star catalog designations and call them Pi, Mu, and the exceptionally picturesque 51 Andromeda. Honestly, was there no one in the whole of antiquity who could come up with an appropriate name for the star marking the maiden’s royal right foot?

The Chained Woman, from Johann Bode's 1801 star atlas

I imagine the celestial princess finds it undignified enough that her left foot is permanently associated with a reclusive predator with rodent breath. Maybe it’s been eating those alpha rats.

Thursday, October 16, 2008

The Little Dolphin

Just east of Altair, the southernmost star in the Summer Triangle, is Delphinus the Dolphin. Although a rather small, unassuming constellation, its distinctive central asterism (recognizable star pattern) actually resembles a leaping dolphin, so it’s fairly easy to spot once you’ve learned it.

Image from Flamsteed’s 18th century star atlas
Courtesy of
Linda Hall Library of Science, Engineering and Technology

Delphinus the Dolphin (dell-FINE-uss) is an ancient constellation. In Greek myth, Delphinus was a messenger of the sea god Poseidon. When Poseidon pressed one of the sea nymphs at his court to marry him, the reluctant goddess fled. The persistent Poseidon sent a number of messengers to persuade her to return and become his wife, but only the beguiling dolphin succeeded. A grateful Poseidon elevated Delphinus to immortality in the night sky.

Star maps created with Your Sky

When I see the jeweled spray of stars that forms the Dolphin asterism high overhead in the early evening, I know that autumn has arrived. Let’s take a closer look at those five stars.

1) If you don’t know how to locate the Summer Triangle, read my earlier post. Look for the sprightly Dolphin a little east of Altair, the brightest star in Aquila the Eagle.

Dolphin asterism in the constellation Delphinus

2) Yellow-white Rotanev (ROH-tuh-nev) is the brightest star in Delphinus. Although slightly dimmer than Rotanev, blue-white Sualocin (SWAH-loh-sinn) is nevertheless the hotter of the two.

When these star names first appeared in an Italian star catalog in 1814, astronomers were puzzled as to their origin. Clever sleuthing by the English astronomer Thomas Webb revealed them to be the reverse spelling of Nicolaus Venator, the Latinized version of the name Niccolo Cacciatore. Cacciatore was the assistant to (and successor to) Giuseppe Piazzi, the famed director of the Palermo Observatory in Italy. It is unclear whether Cacciatore or Piazzi was responsible for the stellar wordplay.

Giuseppe Piazzi is best known as the discoverer of the largest asteroid found in our solar system to date: Ceres (SEER-eez).

3) The other two stars that, along with Rotanev and Sualocin, complete the “head” of the Dolphin asterism have no traditional names, so we call them Gamma and Delta, their star catalog designations. Gamma is a yellow-orange star, and Delta is a white giant.

4) The blue-white giant star that marks the dolphin’s tail is Deneb al Dulfim (DENN-ebb), from the Arabic for, blimey, dolphin’s tail! Now can you see the dolphin frolicking in the foam of the Summer Milky Way?

5) Delphinus contains an asterism within an asterism. The head of the Dolphin asterism— the quadrilateral formed by Rotanev, Sualocin, Gamma, and Delta— is an asterism known as Job’s Coffin. The origin of this odd name is unknown. It’s just another mystery lost to history. Perhaps someone should have put Thomas Webb on the case.

Thursday, October 9, 2008

It's a Bird!

The days of the month surrounding Full Moon can sometimes feel like an astronomical “dead zone.” The floodlight effect of our lunar neighbor on the night sky makes everything from tracing out naked-eye star patterns to telescopic viewing of deep-sky objects difficult to impossible.

Certainly you can enjoy looking at the Moon itself. There are interesting craters to behold with your binoculars or telescope. Naked-eye moongazers with an extra dollop of imagination can look for pareidolia among the Moon’s dark maria or “seas.”

But here’s another diversion for those suffering from Full Moon fever: satellite watching. Many satellites are naked-eye targets, they’re generally bright enough to be seen on moonlit nights, and they travel in predictable orbits. What could be easier?

Image source: NASA

Satellites, colloquially known as “birds,” are man-made objects in orbit around Earth. Typically, they are unmanned communications, navigation, and observation stations. One notable unmanned craft is the Hubble Space Telescope, which regularly returns remarkable, detailed images of celestial objects, for scientific study and public enjoyment.

Some satellites are simply large pieces of space junk. These may include stations that are no longer operational but which continue to circle the planet until their orbits deteriorate, they enter Earth’s atmosphere, and they vaporize before impact (hopefully). Space junk may also include objects that have been jettisoned from manned craft.

Which brings us to the manned station circling the planet: the International Space Station (ISS). The ISS is a 16-country international collaboration: proof positive that human beings can work together for the advancement of the entire human race. This engineering marvel, with a resident multi-national crew on board, completes an Earth orbit every 90 minutes.

International Space Station
Image source: NASA

By the way, the word “satellite” is also used in astronomy as a synonym for “moon,” as in, “Saturn has 34 satellites.” The Moon is sometimes referred to as a natural satellite of Earth.

Image source: NASA

There are two terrific websites that can help you get started with man-made satellite watching. The first one I’ll mention, because it’s the easiest for beginners to use, is Satellite Tracker by Simply enter your zip code on the home page, click the “Go” button, and you’ll get a list of the best-and-brightest satellite flybys in your area over the next ten days. For each flyby, the rise time (when the satellite first appears over the horizon) and the transit time (when the satellite is at its highest in the sky) are both given in your local time. Nope, you won’t have to do any pesky conversions.

You’ll also be given the compass direction in which to look, as well as the predicted magnitude (brightness) of the satellite. You may recall from my previous discussion of the star Vega that objects with negative-number magnitudes are brighter than objects with positive-number magnitudes. However, you don’t need to remember that to use this website; the magnitude is also characterized for you as “very bright,” “visible,” or “dim.” Start with the satellites labeled “very bright,” as you’ll have the best chance of success with these. Once you have a few bright flybys under your belt, work your way up to the “visible” and “dim” objects.

Keep in mind that you’ll only see low-flying satellites such as the ISS (~250 miles above Earth) and the Hubble Space Telescope (~350 miles above Earth) shortly after sunset or shortly before sunrise. Satellites are visible to us only when they’re reflecting sunlight. A low-orbit satellite passing overhead in the dead of night would be in Earth’s shadow, with the Sun on the other side of the planet and no way to receive light from it.

Hubble Space Telescope
Image source: NASA

How can we tell a satellite from a plane? A satellite moves in a straight line and is usually visible for only a few minutes before winking out. A plane will typically be visible for longer, and you may see directional change. Also, a plane will usually have flashing lights and/or colored lights. If it’s close enough and the observing environment quiet enough, you’ll hear the plane’s engine(s). Satellites are silent. Several lights moving in formation are often military craft performing maneuvers.

The second website I’d like to recommend, for intermediate and advanced observers, is Heavens Above. On the home page, select your current observing site “from database” by selecting your country and typing in your town name. When it appears on the search results, click your town name to select it as your location. Then in the “Satellites” section, request your desired satellite predictions. This site also gives you pass results in local time, but it’s expressed in military time. I don’t know about you, but I don’t think in military time. Points taken off for making me do a pesky conversion!

Heavens Above gives prediction data for many more satellites than the Satellite Tracker site, and you can also request data for a specific satellite from their large database. Plus, the website offers much more than just satellite data. The “Astronomy” section has current data about visible comets and asteroids, and lots more.

On the evening of October 8, I took a last gulp of ice tea and hurried out of my local diner with four minutes to spare before a scheduled ISS pass. Soon, my partner, two other customers, a waitress, and a cook joined me in the parking lot to scan the northwestern horizon for the first appearance of the Space Station. Satellite spotting is a great activity to share with adults and kids, friends and perfect strangers.

We had a few false alarms as planes appeared over the horizon, heading for the international airport nearby. One of the customers was the first to whoop, “There it is!” Then we all spotted it, a steadily moving light already well above the horizon. The cook scurried back inside to flip some burgers and answer the phone, while the rest of us watched it climb and waved to the unseen crew inside.

Shortly after it reached the highest point of the pass, the reflected sunlight from the satellite became ruddy-colored. It was sunset on the ISS. From the astronauts’ vantage point as they rounded Earth, the Sun was sinking below Earth’s horizon. Then the satellite was swallowed by Earth’s shadow, and the light winked out.

Just think: if you were a sleepless astronaut on the ISS, over the course of 24 hours you could watch the Sun rise and set many times. Busy old fool, the poet called him.

…since thy duties be
To warm the world, that’s done in warming us.
Shine here to us, and thou art everywhere;
This bed thy center is, these walls thy sphere.
from The Sun Rising, by John Donne

Thursday, October 2, 2008


Although autumn is beginning to nip the air and sweaters are starting to replace tank tops, you can still hold on to that endless-summer feeling a little longer. If you look up after sunset, you’ll find the star pattern known as the Summer Triangle overhead. Like the Winter Hexagon, the Summer Triangle is a seasonal asterism (recognizable star pattern) that spans more than one constellation.

Even in somewhat light-polluted areas, you should be able to spot the three bright stars that define the Triangle, but this asterism is worth a trip to the outskirts of town to view it under dark skies. The Triangle has naked-eye and binocular treasures to plunder, if you’re willing to go the extra mile.

Once you master the Summer Triangle, you will know:
- five constellations
- the brightest stars in three of those constellations
- which star is used as the standard for star brightness
- the direction in which our solar system is traveling
- another prominent asterism
- a notable double star
- a naked-eye star cluster
- a binocular star cluster

This is a great deal. In fact, just think of this as a celestial end-of-summer closeout sale. Hurry hurry hurry!

1) Wait at least one hour after sunset to begin observing, so that twilight’s finished and your sky’s good and dark.

2) Check the time of moonset before you observe. The waxing (growing) Moon will be in the western sky at sunset and will set a bit later than the night before, each night this week. The Moon will also be a bit brighter each night, as the illuminated part of its face increases. Your optimum observing window— for least Moon interference and best placement of the Triangle in the sky after moonset— ends on Sunday night, October 5.

3) Face south. If you don’t know the cardinal directions at your location and you don’t have a compass, make note of where the sun sets on the horizon. That spot is approximately west. Stand with your right shoulder to the west, and you’ll be facing approximately south.

Star maps created with Your Sky

4) Tilt your head all the way back until you're looking at the zenith, the point in the sky that’s directly overhead. Now look for a large triangle formed by three bright stars. It will straddle the zenith or be slightly south of it, depending on your latitude. The sides of the triangle will be two to three fist-widths long. A fist-width is defined here as your fist held at arm’s length against the sky and measured across the knuckles.

5) The stars that mark the points of the triangle are Vega (VAY-guh) in the constellation Lyra the Harp (LYE-ruh), Altair (AHL-tair) in the constellation Aquila the Eagle (uh-QUILL-uh), and Deneb (DENN-ebb) in the constellation Cygnus the Swan (SIGG-nuss).

Vega is Arabic for swooping vulture, Altair is Arabic for flying eagle, and Deneb is Arabic for hen’s tail. Let’s see, Aquila is an eagle, and Cygnus is a swan. Yes, there’s an ornithological motif here, with its roots entwined in the ancient star lore of several cultures.

6) Be careful to identify the correct triangle. It’s possible to be distracted by Rasalhague (RAH-sahl-hayg), the brightest star in neighboring Ophiuchus (oh-fee-YOU-kuss) the Serpent Handler, and to combine it with Vega and Altair. However, Rasalhague is farther west than the three Triangle stars, and it’s not as bright as Deneb.

Another way to ensure you have the correct triangle, with Deneb, is to look for the asterism called the Northern Cross. Deneb is at the top of the cross, and the bottom of the cross terminates inside the Triangle, nearly equidistant from Vega and Altair.

7) Now that you’re sure you’ve found the Triangle, let’s take a closer look at the point stars.

Vega, a white dwarf, is the brightest star in Lyra the Harp and the fifth brightest star in the night sky. Apparent magnitude, how bright a star appears to us from Earth, is one of the ways in which stars are measured, categorized, and compared. Vega is a zero magnitude star, and it’s the standard of brightness to which all other stars are compared. Dimmer stars have a magnitude expressed with a positive number, while stars brighter than Vega have a magnitude expressed with a negative number. It’s just the opposite of how you’d think it would be.

A light year is the distance light travels in one Earth year, nearly six trillion miles. Vega lies 25 light years from Earth, and it just happens to lie close to the solar apex. The solar apex is the point in the night sky toward which our solar system appears to be heading, as it travels around the center of the Milky Way galaxy in a 225-million-year-long orbit.

Altair, also a white dwarf, is the brightest star in Aquila the Eagle. Altair is flanked evenly by two dimmer stars, Alshain (all-SHANE) and Tarazed (TAH-ruh-zedd). The names of both stars are from a Persian phrase meaning scale beam, that is, the balance bar from which a set of scales hangs. This straight line of three stars is easy to pick out in the night sky. In old star atlases, Altair marked the heart of the Eagle. Altair is about 16 light years from Earth, the closest of the three Triangle stars.

Deneb, a white supergiant 200 times the size of our Sun, is the brightest star in Cygnus the Swan. Deneb marks the tail of the Swan, and as we learned earlier, the top of the Northern Cross.

In reality, spectacular Deneb is considerably brighter than either Vega or Altair. It appears to us the dimmest of the three because of its great distance. It’s 2600 light years away— that’s 2600 times six trillion miles. It may be forgiven if its light is a bit weak after that long journey to our eyes.

8) In addition to Lyra, Aquila, and Cygnus, the Triangle also encompasses parts of two minor constellations: Vulpecula the Fox (vull-PECK-you-luh) and Sagitta the Arrow (suh-JEE-tuh). The map above shows the modern boundaries of these obscure old constellations. Don’t worry about identifying the specific stars of these constellations inside the Triangle; it’s enough to know that they’re there.

When the Fox was introduced to star atlases in the 17th century, he was depicted carrying in his jaws a goose. Yet another species for our celestial birdwatching list!

9) Earlier we identified the Northern Cross asterism. The star at the bottom of the Cross, inside the Triangle, is the showy double star Albireo (al-BEER-ee-yoh). Albireo marks the beak of the Swan. Now that you know the location of the beak and tail of the Swan, you can extend the crosspiece of the Northern Cross on either side to visualize the Swan’s outstretched wings.

Albireo is commonly known as the Cub Scout Star. To discover why, you’ll need to examine it through binoculars, 10x50s or larger. Use your binoculars on a tripod if you have one. If not, steady your arms by propping them on a fencepost or other stable object. With sharp focus, you should see a bright gold star with a dimmer blue star nearly touching it. Blue and gold: the Cub Scout colors.

Albireo is a visual double, that is, two stars that appear to be close together but in fact aren’t in proximity and aren’t interacting. Space is three dimensional, and that depth creates many pleasing— albeit deceptive— star pairings, as seen from our earthly vantage point.

10) Now draw an imaginary line between Altair in Aquila and Vega in Lyra. About a third of the way from Altair to Vega is a naked-eye object called Brocchi’s Cluster. Can you see the sparkly patch of light? The object is named for the amateur astronomer who mapped it in the 1920s, although it’s been known since antiquity. Despite its name, it probably isn’t a true star cluster, since its stars don't seem to be related. Rather it’s an asterism, a chance arrangement of stars forming a recognizable pattern.

That pattern is revealed when you view the object through binoculars, as is its other name: the Coathanger. Magnified, the patch is transformed into a whimsical star grouping that resembles a coat hanger. A foxy trick, perhaps, but then the Coathanger does lie in the constellation of Vulpecula the Fox.

The Coathanger
© T. Credner & S. Kohle,

11) Speaking of foxes, let’s find our final target, one of my favorite star clusters: the charming Foxhead Cluster in Cygnus. You’ll need good-sized binoculars for this one; I’d recommend 10x50s or larger. Draw an imaginary line from Vega in Lyra to Sadr in Cygnus. Sadr (SAH-durr) is the star at the center of the Northern Cross. Train your binoculars on a spot that’s a little more than halfway from Vega to Sadr. Look for a triangle-shaped clutch of stars with two bright stars flanking it. The triangular cluster is the Foxhead, and the longer you look at it, the more it begins to resemble the pointed snout and ears of a fox. An overactive imagination can be a great advantage in this endeavor.

The Foxhead Cluster
Image from Sloan Digital Sky Survey

With all those birds flitting around the Triangle, I imagine this wily fox is just biding his time.

12) You hopefully have noticed the long, bright “cloud” of the Summer Milky Way running through the Triangle. The glowing band is a sort of celestial runway for Cygnus the Swan, who appears to be preparing to fly south for the winter.

The Summer Milky Way is our edge-on view of the star-packed arms of our platter-shaped galaxy. In the summer, due to Earth’s location in its orbit around the Sun, we are looking inward, towards the galactic core.

How exciting that we can see, with our naked eyes, some of the structure of that vast star system to which our lucky old Sun— and we— belong.