Thursday, August 28, 2008

Crowning Glory

Due east of Arcturus, the orange giant star we examined last week, is a pretty, horseshoe-like arrangement of stars. The Horseshoe is the central asterism, or star pattern, of the constellation Corona Borealis (bore-ee-AL-iss) the Northern Crown.

Sometimes called “Ariadne’s Crown”, its legend has been known since at least the 5th century BCE. Ariadne was the mythical princess of Crete, an island in the Mediterranean Sea near Greece. The crown was reportedly a gift from the wine god Dionysus, who loved her.

You may recall the ancient story of the Minotaur, the half-man, half-bull who lived at the center of a labyrinth or maze. This was Ariadne’s gruesome half-brother, to whom seven men and seven women had to be sacrificed each year. It was Ariadne’s magic ball of twine that enabled one of those men, the hero Theseus, to find his way both into and out of the labyrinth so he could slay the Minotaur.

Two star atlas depictions of Corona Borealis

The Grecian crown has been depicted as both a traditional, jeweled crown and a wreath of flowers, but other cultures saw the curved star pattern quite differently. The aborigines of Australia called it the “Boomerang,” and the early Arabs called it the “Beggar’s Bowl.”

Chart created with Your Sky

Under dark skies, away from city lights, you should see seven stars forming the curve of the Horseshoe. The brightest one has two names: Alphecca (ahl-FECK-uh) and Gemma (GHEMM-uh). Alphecca is Arabic for broken one, a reference to the semicircle of stars. Gemma, a star name adopted later, is Latin for jewel. This luminous white star is also known as the “Pearl of the Crown.”

The star to the right (northwest) of Alphecca is Nusakan (nuss-uh-KAHN), the second brightest star in Corona Borealis and a yellow-white dwarf star. Nusakan is from the Arabic for two lines of stars, which has nothing to do with its crown-jewel status but is instead a reference to an ancient Arabic constellation.

Stargazers in the southern latitudes of the country can challenge themselves by looking for the other celestial crown: the faint Southern Crown, Corona Australis (aw-STRAH-liss). You’ll find it hanging beneath Jupiter and the Teapot asterism of the constellation Sagittarius the Archer, low over the southern horizon. As shown below, this crown was sometimes depicted as a wreath of myrtle leaves, a plant closely associated with none other than Ariadne’s main squeeze, Dionysus.

Star atlas depiction of Corona Australis
Courtesy of
Linda Hall Library of Science, Engineering and Technology

Thursday, August 21, 2008

Arc to Arcturus

If you can locate the Big Dipper, you can easily locate the brightest star in our summer sky, Arcturus (ark-TOUR-uss). One of the first memory prompts that beginning stargazers learn is “arc to Arcturus.” Just extend the curve of the Big Dipper’s handle to the next star in that line that's brighter than the end star of the handle, and you’ll arc to Arcturus.

Chart created with Your Sky

Right now, Arcturus is also easy to spot if you simply face west one hour after sunset. Arcturus will be the brightest object in the western sky. At that time, planet Jupiter will be the only object in the sky that’s brighter; it’s the blazing star-like object in the southeast, over your left shoulder, so you shouldn’t confuse the two.

Arcturus is the fourth brightest star in the night sky, after Sirius (SEER-ee-uss), Canopus (kuh-NOPE-uss), and Alpha Centauri (senn-TARR-ee). Sirius is a winter star, and Canopus and Alpha Centauri are Southern Hemisphere stars. So, in the summer sky of the Northern Hemisphere, Arcturus rules.

Big and brilliant, Arcturus is 25 times the diameter of our Sun and 113 times as luminous. This orange giant star is the brightest luminary in the constellation of Bootes (Boh-OH-teez) the Herdsman. Arcturus is Greek for “guardian of the bear,” a reference to the star’s ancient association with its neighboring constellation Ursa Major (ER-suh). Ursa Major is the Great Bear, and the Big Dipper is the central star pattern or asterism of Ursa Major. Arcturus appears to trail the Great Bear, which moves counterclockwise around Polaris, the North Star. So you can see how fitting it is that we arc to Arcturus from the Big Dipper.

Arcturus lies 37 light years from Earth. A light year is the distance light travels in one Earth year, nearly six trillion miles. When you observe Arcturus, what hits your eyes is light that departed the star 37 years ago. You are receiving vintage starlight from 1971--starlight that began its journey the year that:

- China was admitted to the United Nations
- the voting age in the U.S. was lowered to 18
- Walt Disney World opened in Florida
- cigarette advertising ended on television
- Jim Morrison, lead singer of The Doors, was found dead in Paris
- Intel released the world’s first microprocessor
- Idi Amin took control of Uganda
- pocket calculators, floppy disks, and e-mail were invented
- the films Love Story and The French Connection were in the theaters
- Federal Express and Greenpeace were launched
- platform shoes and crushed velvet hot pants were all the rage

Stars are time capsules, and Arcturus is seriously retro.

Thursday, August 14, 2008

Moon Tunes

This week, I offer you seven days of song, in celebration of the Full Moon that falls on Saturday, August 16. Here’s a septet of my favorite tunes with “moon” in the title.

7) Moonshadow, performed and written by Cat Stevens

The artist formerly known as Cat Stevens wrote this pop hit--considered by many to be an anthem to optimism--while dancing alone in the moonlight on the Spanish seacoast. The song appeared on his 1971 album Teaser and the Firecat.

6) Fly Me to the Moon, performed by Frank Sinatra, written by Bart Howard

The boy from Hoboken practically invented cool, and he swings on this tune from his 1964 album It Might As Well Be Swing. Sinatra’s cover of the 1954 song, already recorded by Johnny Mathis and others, featured a Quincy Jones arrangement and accompaniment by Count Basie and his orchestra. When astronaut Eugene Cernan and a friend made a cassette recording of various popular tunes for Cernan to take into space on the Apollo X mission, they included Sinatra’s version.

5) Moonglow, performed by Benny Goodman, written by Hudson/Mills/DeLange

The only instrumental on my list is from the King of Swing, clarinet virtuoso Benny Goodman. An important figure in 20th century American music, he ushered in the era of swing in the 1930s and played the first jazz concert performed at Carnegie Hall. He was awarded a posthumous Grammy for “Moonglow” in 1998. Goodman’s clarinet will make you sway like a charmed snake, and Lionel Hampton’s killer vibraphone will make you hum like a tuning fork.

4) Blue Moon of Kentucky, performed by Patsy Cline, written by Bill Monroe

The immortal Patsy rollicks her way through this country music standard from bluegrass great Bill Monroe. Recorded in 1963, the year of her untimely death, it was released posthumously the following year on the album A Portrait of Patsy Cline.

3) Moondance, performed and written by Van Morrison

This warm, romantic fusion of rock and jazz is from the 1970 masterpiece album of the same name. With it, Irish bard and consummate musician Van Morrison secured his place in the pantheon of popular music.

2) Bad Moon Rising, performed by Creedence Clearwater Revival, written by John Fogerty

From the 1969 album Green River, this is simple, earthy, hard-driving swamp rock from a great American band. John Fogerty’s voice had me at hello.

1) Moon River, performed by Andy Williams, written by Henry Mancini/Johnny Mercer

Call me sentimental, but I can’t resist this sweet ballad and its evocation of my childhood. Famously sung by the reedy-voiced Audrey Hepburn in the classic film Breakfast at Tiffany’s, it won the Academy Award for Best Original Song of 1961. Andy Williams performed it at the Oscars ceremony and made the song his own. Although it’s been covered by countless artists, I remain partial to Williams’s honeyed baritone and flawless phrasing.

What’s your favorite moon-titled song? Add your comment below, and keep on shining.

Thursday, August 7, 2008

The Pursuit of Perseids

The Perseids (pronounced PURR-see-yidds) are a major, reliable meteor shower and one of my personal favorites. It simply wouldn’t be August if I didn’t try to spot some of those long, yellow-tailed beauties streaking across the sky.

Sometimes a big Moon will thwart or at least hamper my attempt. That’s the case this year. The peak of the meteor shower--when the number of meteors per hour is greatest--is predicted to occur in the early morning hours of Tuesday, August 12. As this is less than one week before Full Moon, the waxing (growing) Moon will be in a gibbous phase. Gibbous means the Moon is greater than 50% illuminated without being fully illuminated. In other words, a big Moon.

A big Moon tends to wash out the sky, reducing the contrast needed to see faint streaks of light. No Moon is optimum. Since the Moon doesn’t set until two to three hours after midnight (depending on location) on the morning of the 12th, you’ll have a narrow window of opportunity to spot peaking Perseids before morning twilight lightens the sky. But the reward will be great: the predicted peak rate is 100 meteors per hour!

By all means, don’t get too hung up on peak predictions. I’ve seen some awesome meteor shower displays on nights prior to and after the so-called peak. In some cases, I was pleasantly surprised to discover they bested the peak display. The Perseids are active this year through August 24. Pick any night from now until then, go out after midnight when the Moon’s not around, and you’re bound to see some dreamy Perseids.

There’s a reason why I specified “go out after midnight” above. Perseids emanate from, and are named for, the constellation Perseus (pronounced PURR-see-yuss). The show can’t begin until the radiant in Perseus rises above the northern horizon. The radiant is the point in the constellation where the Perseids appear to originate. The higher the radiant rises in the sky, the more likely you'll see meteors. The radiant is well above the horizon--and rising--from midnight through dawn.

The radiant is marked on the map below. Despite their origination point, you can see Perseids in any part of the sky, in any direction you happen to be looking. However, knowing the radiant will help you identify which “shooting stars” are Perseids and which are sporadics, meteors not associated with a particular meteor shower. If you can trace a meteor’s trajectory back to Perseus, it’s most likely a Perseid.

Chart created with Your Sky

1) Go to as dark of a site as you can, with no line-of-sight outdoor lights. Take extra layers of clothing or blankets with you. Even though it’s summer, you won’t be moving around much and could get chilled.

2) Take a lounge chair or a blanket for the ground. Reclining is really the best way to watch a meteor shower, because it allows you to see the most sky at one time. Although the meteors originate from the radiant, you can see them fizzling anywhere in the sky. I normally lie with the top of my head pointed toward the rising radiant (which will be in the northeast) so that I can be scanning the rest of the sky.

3) A meteor is the streak of light caused when a bit of interplanetary dust, comet debris, or manmade space junk slams into Earth’s atmosphere at high velocity. Typically, the meteoroid--the bit of debris--vaporizes upon impact with the atmosphere. But occasionally, a large chunk may survive its screaming 100,000-plus mph entry and hit the ground, at which point we refer to it as a meteorite.

As you watch the fireworks, keep in mind that meteors are typically no bigger than a grain of sand. The really bright ones that go off like Roman candles may be no bigger than a grain of rice. It is their high entry velocity that causes the wonderful light show.

4) A meteor shower occurs when Earth encounters a stream of debris left behind by a comet’s close approach to the Sun. Comet Swift-Tuttle takes 135 years to complete its orbit of the Sun. Each time it approaches, the Sun's heat releases dust trapped in the comet's icy nucleus or frozen center. This periodic renewal of the discarded dust stream ensures us cosmic fireworks every August when we move through it.

Meteor showers are one of the supreme naked-eye treats for lounge-chair astronomers everywhere, beginners to veterans. Do make the pursuit of Perseids part of your summer recreation. Do make a memorable evening with a friend or family member. Don’t forget to make a wish.