Thursday, July 31, 2008

Something Old, Something New

This year, I began searching for something old and something new. No, I wasn’t outfitting myself for a traditional wedding. I was searching the sky for two celestial objects that fit squarely (or roundly, as the case may be) in the observing category I call “Things That Are Barely There.”

These two objects are really two manifestations of the same object: the Moon. New Moon is when the Moon’s too near the Sun in our sky to be visible. My quarry was an extremely young crescent Moon, less than twenty-four hours after New Moon, and an extremely old crescent Moon, less than twenty-four hours before New Moon. These are notoriously difficult to see. Imagine the thinnest slice of green cheese you can, and you’ve got the picture.

Something New

The very young waxing (growing) crescent Moon must be spied in the narrow window between sunset and moonset. On February 7, I realized I could snare a less-than-one-day-old Moon that evening. I made this determination by consulting the U.S. Naval Observatory’s Sun and Moon Data website. I find it to be an invaluable observing aid, and you’ll find a link to the site in most of my blog posts.

After entering my location and the date, I pulled up the relevant Sun/Moon data sheet. As you see in the image above, I had a 45-minute window between sunset and moonset. I knew that New Moon had just passed, and the data sheet confirmed it at 8:44 p.m. the previous evening. That meant at moonset (6:32 p.m.)--the last possible time to see the young crescent--it would be less than 22 hours old. It would also be a sliver. Note the data sheet says “waxing crescent with 0%…illuminated.” That meant the Moon’s face would be less than 1% illuminated and an elusive target.

Western horizon before sunset on 2-7-08
Chart created with
Your Sky

Armed with 10x50 binoculars and a more experienced observing partner, I drove to a location with a good view of the western sky. Because we knew the Moon follows approximately the same path across the sky as the Sun, we took note of the slanted path of the setting Sun (never look directly at the Sun!). We also noted precisely where the Sun set, relative to the land features. After the Sun was safely below the horizon, we began using the binoculars to scan for the meager Moon we knew was traveling in the Sun’s wake. We searched for 15 minutes, racing against the celestial clock, and then we spied it. It was breathtakingly slender, a curving piece of thread in a dusky sky. We tried, but weren’t able, to see it naked eye in the too-bright twilit sky. We took turns savoring it through the binoculars for the next 15 minutes. Then it disappeared behind the ridge to the west, sucked down like a strand of spaghetti.

Something Old

This morning, July 31, 2008, I attempted to complete my set. A very old waning (shrinking) crescent Moon must be spied in the narrow window between moonrise and sunrise. The USNO site gave me a one-hour window between the two. If still visible at sunrise (6:17 a.m.), the old crescent would be only 22 hours shy of New Moon.

Equipped this time with the same 10x50 binoculars and observing partner, plus an eight-inch reflector telescope, I drove to a spot with a good view of the eastern sky. I had with me a sky map showing where the Moon would rise relative to the eastern stars. Luckily, Castor and Pollux, the two brightest stars in Gemini, would make a line pointing to the twiggy Moon’s entrance.

Eastern horizon before sunrise on 7-31-08
Chart created with Your Sky

We waited for moonrise. A somber owl hooted again and again. A distant pack of coyotes yipped and barked. We enjoyed various galaxies and globular clusters in the telescope, as well as the naked-eye treat of zippy Delta Aquariid meteors emanating from the constellation Aquarius. If you can get to a dark-sky location, the “shooting stars” of this meteor shower will be active until August 19. They are short and swift, but I did see one that left a glowworm trail lasting for several seconds.

At the appointed minute of moonrise, we began searching--I with binoculars and my partner with telescope. It took several heart-pounding minutes for the crescent to clear the low mountain ridge to the east. Finally, I heard “Got it!” to my left. It was in the telescope. About 15 seconds later, I bagged it in the binos, just lifting off the ridge. Then we both spotted it naked eye, a mere wisp in the rapidly lightening sky.

Very Old Moon of 7-31-08

In the telescope, the lunar sliver was scintillating orange and green, much like a twinkling star scintillates in atmospheric murk near the horizon. As it rose, we began to see the faintest hint of craters in the sliver. I held my digital camera near the telescope’s eyepiece, carefully moving it around and snapping a photo each time the crescent floated into the viewfinder. A tripod would’ve been just the ticket; it was difficult to keep my hands steady. But I bagged my precious trophy, nonetheless.

At twenty-five minutes to sunrise, the naked-eye crescent was no longer visible in the pale blue sky. We continued to watch the Moon through the telescope. I wondered aloud if we would still see it at sunrise. The tessellated clouds overhead shifted from gray and white to rose and cream.

At the minute of sunrise, the Moon looked like a cat’s whisker in a bowl of milk, but we could still see it. The Sun was still blocked behind the eastern mountain ridge. We had the whisker for five minutes past sunrise, then it vaporized.

But the show wasn’t over! We suddenly noticed a bright object over the eastern ridge. At first we thought it was Venus, until we slapped our punch-drunk selves awake, remembering that Venus was currently too close to the Sun to be visible. Aha, could it be? Sure enough, a look through the telescope confirmed the bright, bulbous shape of a weather balloon. Something serendipitous.

Thursday, July 24, 2008

Fishing for Scorpion

Scorpius the Scorpion is one of those rare constellations whose prominent star pattern actually resembles the figure it represents. The ancient Greeks, Arabs, Persians, and Turks all saw a starry scorpion in the pattern. It’s easy to see why. The long, lazy curl of stars that punctuates the constellation at its southern end looks like a scorpion’s toxic tail. Although this dramatic feature is easy to spot, it may not be wholly visible to skywatchers in the far northern latitudes, because Scorpius sits low in the south.

Image by Jim Kalisch

In Greek mythology, the scorpion was the infamous creature that stung Orion the Hunter to death. The prodigious huntsman had boasted that he could and would kill every wild animal in existence. This angered the gods, who dispatched the stealthy scorpion to do their dirty work. Afterwards, king of the gods Zeus placed both Orion and Scorpius in the sky, ensuring that the Hunter (winter constellation) was never in the sky at the same time as the Scorpion (summer constellation). They chase each other around the celestial sphere for eternity.

Scorpius in 19th century star atlas

Let’s see if we can spy the scorpion, while avoiding the business end of that sinister tail.

1) You’ll need to 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) Wait at least one hour after sunset to begin observing, so that twilight’s over and your sky’s good and dark. On Thursday the 24th, you’ll have a couple dark hours to stargaze before the gibbous Moon rises. The Moon is considered gibbous whenever its face is more than half illuminated but not fully illuminated. On Friday the 25th, the Moon’s phase will be Last Quarter (commonly called a “half moon”), and it’ll rise around midnight. Each night for the rest of our observing week, the Moon will rise a bit later with its illuminated part continuing to shrink or wane.

3) Looking due south, you should see a tall curve of stars that hooks over to the left (east) after it skims the horizon. This is the asterism (recognizable star pattern) known as the Fishhook. It’s also the torso and tail of the mythological scorpion.

4) Let’s begin our survey of the Fishhook at the top, with the stunning red supergiant star Antares (pronounced ahn-TAHR-eez), brightest star in Scorpius. Due to its deep red color and its position in the imaginary scorpion’s body, Antares is commonly called the Scorpion’s Heart.

The name Antares is from the Greek for like Mars. Planet Mars periodically enters Scorpius and passes near Antares. The red planet and the red star can easily be mistaken for one another.

Luminous Antares is 10,000 times brighter than our Sun and much larger. If Antares were dropped into our solar system in place of the Sun, it would extend beyond the orbit of Mars, engulfing that planet along with Mercury, Venus, and Earth. Immense Antares is a candidate for death by supernova, a cataclysmic explosion that occurs when a massive star reaches the end of its life cycle.

5) Below Antares, nine bright stars wind around to form the Fishhook before it terminates in a glowing barb composed of a close-set pair of stars. This terminal pair is an asterism called the Cat’s Eyes. It’s also the stinger of the legendary scorpion. The eastern star in the pair is the second brightest star in Scorpius, Shaula (pronounced SHOWL-uh). Shaula is Arabic for stinger. The fainter western star is Lesath (pronounced LESS-utt), Arabic for sting. Although Shaula and Lesath appear cozy from our two-dimensional viewpoint, they’re more than 150 light years apart and don’t interact. We often forget to apply the third dimension of depth when we see visually pleasing star patterns.

6) The third brightest star in Scorpius is Girtab, riding low on the Fishhook where it turns up toward the Cat‘s Eyes. Girtab (pronounced GRRR-tahb) is from the Sumerian for scorpion. This yellow-white giant star can’t be seen from above 50 degrees north latitude, so folks in Spokane, Washington and Utica, New York will see an interrupted Fishhook dip below the horizon.

7) If you’re observing from a dark-sky location, try this naked-eye challenge. Can you spot the two star clusters just northeast of the Cat’s Eyes? They should look like fuzzy patches of light. They’re both open clusters. An open cluster is a family group of sorts, a loose collection of stars that formed around the same time in the same nebula, or cloud of gas and dust.

The cluster closest to Shaula, known as Messier 7 (pronounced MESS-ee-yay) or Ptolemy’s Cluster, is also the brighter of the two. It contains approximately 80 stars and was named for the ancient Greek astronomer Ptolemy (pronounced TAHL-uh-mee), who wrote about it in the year 130.

The naked-eye cluster slightly north and west of Messier 7 is called Messier 6 or the Butterfly Cluster. This whimsical cluster also contains around 80 stars whose arrangement, when viewed through binoculars, suggests a butterfly. The fainter Butterfly Cluster glimmers from nearly twice the distance of Ptolemy’s Cluster.

Ptolemy’s Cluster (lower left) and Butterfly Cluster (upper right)
Copyright T. Credner,

8) Our expedition wouldn’t be complete without a dip in the Summer Milky Way. Can you see the misty stream that rises from the southern horizon, winds behind the Fishhook and the two clusters, and then stretches northward across the sky? What we call the “Summer Milky Way” is only one arm of the pinwheel-like galaxy we inhabit. The hazy, mottled arm is a horde of stars too numerous and faint to be resolved into pinpoints with the naked eye. Because the southern part of that arm--the Sagittarius Arm--lies in the direction of the dense galactic core, Scorpius occupies an area of the sky teeming with deep-sky delicacies ready to be hooked with telescope and binoculars.

Gone fishing.

Thursday, July 17, 2008

Moon in the Balance

I am torn.

As an amateur astronomer, I must arrange my observing life around avoidance of the Moon; wait impatiently for it to set; nervously watch the eastern horizon for its arrival; hide from it behind trees, rock outcroppings, vehicles, and outhouses; wail and curse it when it appears. Let’s face it, that old incandescent Moon is the bane of every hunter of "faint fuzzies": deep-sky objects pursued with telescopes, binoculars, and much lurching about in pitch-dark places.

Faint Fuzzies: Hickson 44 galaxy group

As a human being, though, I must marvel at the Moon and think how lucky we are. We have a natural satellite that shows us, through its phases, that it revolves around us. When it covers the Sun during a solar eclipse or moves into the Earth’s shadow during a lunar eclipse, we have a glimpse into the clockwork of the universe. We have a naked-eye view of the surface of another solar system body. We even have a cosmic timepiece that ticks along reliably enough to give us the basis for our system of calendar months. (Did you know the word month is derived from the Old English word for moon, mona?)

The approach of Full Moon on Friday the 18th has me pondering what I’d do if given the power to choose between keeping the Moon or banishing it forever. A giddy free-for-all of deep-sky diving, unfettered by the lunar cycle, versus a glowing orb that has inspired humans throughout history to pen poems, create art, write songs, do science, and pitch woo. The everlasting happiness and gratitude of my stargazing brethren versus the artistic, scientific, and romantic outpourings of the human race. It would be a tough call.

There are some practical reasons to keep the Moon. In a previous post, I discussed precession, the slight wobble of Earth’s axis. This wobble is caused by gravitational tugging by both the Sun and the Moon. If the Moon were removed from the picture, Earth’s wobble would destabilize, becoming more erratic and pronounced. This would most likely result in dramatic climate changes.

Image courtesy of

Another reason to hang on to our satellite has to do with tides. The combined gravitational pull of Sun and Moon causes the cyclical rise and fall of Earth’s oceans, the tides. Although the removal of just the Moon would not eliminate the tides, it would certainly disrupt them. The feeding and breeding activities of various marine and shore creatures could be severely impacted.

Even if we subtract these practical considerations from the equation, ultimately I think I’d miss the Moon if it were gone. I’d miss how the waxing crescent looks like a big, happy tangerine slice before it sets, and a crescent in the clouds like a shark fin slicing through seafoam. I’d miss that loopy Moon illusion that makes the rising Full Moon look unnaturally big. I’d recall the lunar eclipses I’ve watched and how the Moon in Earth’s shadow always turned red--sometimes russet, sometimes scarlet. I’d miss the gasps and whoops that a telescopic view of the Moon’s crater-pocked surface elicits at public astronomy events. I’d miss my own telescopic tramps across the Moon and moments of discovery. Strangely, I think I’d even miss the collective groan that rumbles across a star party’s observing field when the Moon bobs up in the east.

Observing field at a star party

So, at the end of the day, with all that fateful power at my fingertips, I’d have to give La Luna the thumbs-up. Of course, I’d also have to change my name, move out of state, and never show my face at another star party. Anywhere. Perhaps we should keep this just between us.

Thursday, July 10, 2008

Mister Big

Planet Jupiter is, after the Moon, the brightest object in the evening sky right now. The king of the planets is the blazing "star" rising in the southeastern sky. One hour after sunset, Jupiter’s altitude, or distance above the horizon, is about the height of your fist held at arm’s length and oriented with your thumb on top. Over the course of a night, it will appear to move across the sky from east to west, climbing to two or three fist-heights, depending on your latitude. For skywatchers in Fargo, North Dakota, for example, it will climb to about two fist-heights. Folks cruising Old Route 66 through Albuquerque, New Mexico will see it climb three fists high as it arcs across the southern sky.

Credit: NASA, Reta Beebe, and Amy Simon (New Mexico State University)

This is a great time to observe Jupiter. It reached opposition on July 9, so it’s particularly bright right now. Any planet with an orbit farther from the Sun than Earth’s is said to be “at opposition” when the planet, Earth, and the Sun are lined up so that Earth is in the middle. In other words, the planet is directly opposite the Sun, from our viewpoint. The effect for us is that Jupiter’s face is fully illuminated by the Sun.

In addition, a planet at or near opposition is at its closest to Earth. This closeness gives Jupiter a slightly larger apparent size, the amount of sky it covers from our perspective on Earth. The larger the apparent size, the more illuminated surface to shine light in our direction.

Like all the planets, Jupiter doesn’t have its own light source. It is merely reflecting light from the Sun, and therein lies a little irony. You see, Jupiter is a stellar wannabe. It’s hot and it’s massive, but when the solar system was forming, it wasn’t quite massive enough for nuclear fusion to ignite in its core. Nuclear fusion is the engine that makes a star--like our Sun--go. And Jupiter, although impressive, didn’t have star power.

What Jupiter does have is take-no-prisoners gravity. Its colossal size (1,300 Earths would fit inside) and significant mass (greater than the other seven planets combined) make it the shield of the inner solar system, which includes our little blue planet. If it weren’t for Jupiter, Earth might not have survived the chaos of the early solar system. Countless asteroids and other rogue bodies that might have pulverized Earth were sucked in by Jupiter’s strong gravitational pull and neutralized. The mighty planet protects us still. In the early 1990s, it ripped a comet into 21 fragments and then swallowed them all.

Naked eye, Jupiter looks like a brilliant star. But a sky tourist with a telescope--even a modest one--can see the “star” magnified into a planetary disk and can have fun hunting some of the planet’s features. Dense, colored cloud bands on Jupiter’s surface are exciting to spot in a telescope. Ammonia, methane, and other chemical compounds in its upper atmosphere create the striped look.

Great Red Spot (on right) and Red Spot Junior (on left)
Credit: NASA, ESA, I. de Pater and M. Wong (University of California, Berkeley)

Another famous surface feature is the Great Red Spot, a hurricane-like storm that’s been observed swirling high in Jupiter’s atmosphere for at least 300 years. Red Spot Junior, a smaller storm, appeared nearby in 2006. Because Jupiter spins, the Red Spots are not always in view. To calculate when they’ll be visible, visit this web page.

Jupiter and Ganymede
Credit: NASA/JPL/University of Arizona

Like any good kingpin, Jupiter has a large number of lackeys--in this case, more than 60 moons in tow. In a telescope or binoculars, you can easily spot the four largest, the Galilean moons. These are the moons discovered when the 17th century Italian astronomer Galileo first turned a telescope toward the night sky. They’re named Ganymede (GANN-uh-meed), Io (EYE-oh), Callisto (cah-LISS-toe), and Europa (your-ROPE-uh), after characters in Greek mythology. They look like tiny pinpoint stars near the planet. Occasionally, one or more will be hidden behind the planet as they orbit around. To calculate and view their positions at any given time, visit this web page.

Aurora at Jupiter's north pole
Credit: NASA/ESA, John Clarke (University of Michigan)

In the distant future, when interplanetary tourists can book a solar system cruise, Jupiter will be one of the more exotic ports of call. Imagine cruising over the unlit night side of the planet to watch ultra-powerful lightning storms animate the cloud tops. Imagine flyovers of the north and south poles to view immense auroras: pulsating sheets of neon-colored light. Imagine diving through the barely detectable band of microscopic dust that encircles Jupiter, a vast ring system ethereal as smoke. Everything about Jupiter is king-sized.

Hidden under the swirling gasses of Jupiter’s atmosphere is a voluminous sea, but no one will ever build a resort or bathhouse there. The air pressure and temperature are so extreme there that Jupiter’s abundant hydrogen--normally a gas--has become liquid. Beneath the sea of liquid hydrogen is liquid metallic hydrogen, a bizarre substance unknown on Earth. The crushing pressure at that layer is three million times that of Earth’s surface.

Credit: NASA/JPL/Space Science Institute

Jupiter is the first object I ever observed through a telescope. The impact of seeing with my own eyes the surface of another planet--hundreds of millions of miles away, with colored bands and moons to boot--is hard to describe. I can tell you this: the image in my head will stay with me forever. By the way, this was years before I owned my own telescope. Begged and borrowed views are often the best.

Thursday, July 3, 2008

I Love A Parade

One of the best parades you can see this Independence Day Weekend won’t involve marching bands and won’t require street closures. This parade will take place in the night sky.

Moving in tight formation throughout our observing week will be the waxing (growing) crescent Moon, planet Mars, planet Saturn, and the Lion’s Heart, the brightest star in the constellation Leo the Lion.

Celestial alignments like this one give us a glimpse into the clockwork of the universe. The changing phases of the Moon remind us we’re part of a three-body orbital system: Earth, Moon, and Sun. If we don’t remember to look up occasionally, it’s easy to forget that everything in the universe is in motion, all the time.

To see the alignment, you’ll need to face west, the direction where the Sun sets. Start observing right after sunset. The first object you’ll spot is the crescent Moon. Your ability to spot stars in evening twilight will determine how long it takes you to spot the other three objects. The planets will look like bright stars. Because of their order of brightness, you’re likely to spot Saturn next, then the Lion’s Heart, and finally Mars when the sky darkens enough.

1) On Friday the 4th, the Moon will set about an hour and a half after sunset, so you’ll need to snag it quickly. Its distance above the horizon at sunset will be about the height of your fist. Make a fist and hold it at arm’s length in front of you, with your thumb at the top. Place the bottom of your fist at the horizon or about where you think the horizon is, if it’s obscured by land forms, vegetation, or buildings. Look for the thin crescent Moon at or slightly above the top of your fist.

When you spot it, be sure to look for earthshine. 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.

Western sky at sunset on July 4
All sky charts created with
Your Sky

About a fist and a half above and to the left of the Moon will be the star Regulus, the Lion’s Heart. Regulus (pronounced REGG-yoo-luss) is Latin for little king. This regal star marks the position of the celestial king-of-the-jungle’s heart. Mighty Regulus is 140 times brighter than our Sun.

Continuing on that same diagonal line, just beyond Regulus will be reddish Mars, and just beyond Mars will be golden-colored Saturn.

2) Saturday the 5th will boast the best alignment of the week. This is the one to observe, if your weather permits. The Moon will scoot up to close the gap with Regulus, and you’ll now find the crescent about two fists above the horizon. It’ll be quite a spectacle to see the Moon, Regulus, Mars, and Saturn in a neat diagonal line, close to one another. This isn’t an everyday occurrence!

Western sky at sunset on July 5

Keep in mind that this apparent closeness is an optical illusion. Although we can’t see it, the night sky is three-dimensional. The Moon is only a quarter of a million miles from Earth, Mars is now 200 million miles away, Saturn is now 750 million miles away, and Regulus--the only alignment object not in our solar system--is 77 light years away. One light year is the distance light travels in one Earth year, nearly six trillion miles. Multiply that times 77, and you get a number that makes your head hurt.

Western sky at sunset on July 6

3) On Sunday the 6th, the Moon will break formation and will pull up next to Saturn and Mars. Remember, the Moon is always revolving around Earth from west to east, completing one orbit in about a month (29.5 days). So each night at the same time, the Moon will have moved a bit to the east.

Western sky at sunset on July 7

4) On Monday the 7th, the Moon--now 26% illuminated--will continue on its journey east, pulling past the huddle of Regulus, Mars, and Saturn. You may also notice the gap between Mars and Saturn beginning to close.

Western sky at sunset on July 8

5) On Tuesday the 8th, the Moon will be even higher in the sky at sunset. Mars continues to close in on Saturn.

Western sky at sunset on July 9

6) On Wednesday the 9th, the Moon will reach First Quarter phase (sometimes called “Half Moon”), when it's 50% illuminated. It will be nearly midway in its eastward trip across the sky. Mars and Saturn will look as close as two cosmic peas in a pod. But they’ll appear their closest on Thursday the 10th, as Mars--which has a smaller, faster orbit than Saturn--speeds past the ringed planet.