What's Up this Week: December 11 - December 17, 2006
Written by Fraser Cain
Greetings, fellow SkyWatchers! We'll start off the week in living color and end it fishing for galaxies in Pices. Along the way, we'll have a look at the dark side as we study obscuration nebula… and you won't have to say "Betelguese" three times to study this bright star! If you were disappointed in missing this year's Leonid meteors, then you better watch out and you better not pout… Because the Geminids are coming to town! I'll race you to dark skies, because…
Here's what's up!
Monday, December 11 - On this date in 1863, Annie Jump Cannon was born. Her work led to the modern system of classifying stars by spectra. Tonight let's celebrate her achievement by viewing some stars that have unusual visual spectral qualities. Use a star chart and locate Mu Cephei. Nicknamed the "Garnet Star," it is perhaps one of the reddest stars visible to the unaided eye. At 1200 light-years away, this spectral type M2 star shows a delightful blue-purple "flash." If you still don't perceive color, try comparing Mu to bright neighbor Alpha, a spectral type A7, or "white" star. If you'd like something a bit more unusual, then head for S Cephei about halfway between Kappa and Gamma toward Polaris. Its intense red makes this 10th magnitude star an incredibly worthwhile hunt.
To see an example of a B spectrum star, look no further than the Pleiades…all the components are blue/white. To try orange, look to Aldebaran, or Alpha Tauri, and say hello to a K spectrum star. Now that your curiosity is aroused, would you like to see what our own Sun would look like? Then look no further than Alpha Aurigae, better known as Capella, and discover a spectral class G star - 160 times brighter than Sol. If you're enjoying the game, then have a look at one of the most unusual spectral stars of all - Theta Aurigae. Theta is a B class, or a blue-white, but instead not because of having the usual strong lines of helium. Its abnormal concentration of silicon makes this incredibly unusual double star seem to glitter like a "black diamond."
Still no luck with "stars of color?" Don't worry, it takes practice. The cones in our eyes are color receptors. When we are in the dark, the color-blind rods take over. By intensifying the starlight through a telescope or binoculars, we can usually excite the cones in dark-adapted eyes to perceive color.
Tonight is also the peak of the Sigma Hydrid meteor stream. Its radiant is near the head of the Serpent and the fall rate is 12 per hour - but these are fast and faint. Practice looking for color in them, too!
Tuesday, December 12 - Let's return to Pegasus tonight and continue our galactic hunt.
We will be studying NGC 7741 about three degrees due south of 78 Pegasi. This extraordinary 11.4 magnitude spiral is 30 million light-years away and reveals one of the most unusual bar and spiral structures imaginable. Photographs shows what looks like an old vinyl record with a bright scratch from one side to the other and broad, luminous, near concentric outer grooves. Most mid-sized telescopes will sense the edge of unusual, rectangular spiral extensions. Large scopes will reveal hints of its true nature as an oddly shaped hub and wheel of luminosity in space. Use low and medium powers to view this oddity!
Wednesday, December 13 - Today in 1920, the diameter of a star was first measured by Francis Pease using an interferometer at Mt. Wilson. His target was Betelgeuse. Tonight let's have a look at the giant star in the northeastern corner of Orion. Rising just after skydark, Betelgeuse is winter's brighter and larger version of Antares. Like many red giants, it is inherently unstable - varying irregularly by as much 1.3 magnitudes in cycles up to six years in length. At its brightest, Betelgeuse can appear more luminous than Rigel and its diameter could encompass all the inner planets and much of the asteroid belt. Due to low density, observers would have a hard time determining where space ended and the star began! Allowing for all ranges of radiation, Betelgeuse is more than 50,000 times brighter than our own Sun. Like Antares, it is a "star within a star" - its dense core region radiating with such ferocity that internal pressure drives matter away. Betelgeuse's core has probably fused all its hydrogen and is now releasing energy through helium fusion - resulting in atoms essential to organic life (carbon and oxygen). Even though it hasn't gone supernova yet, when it does it will outshine the Moon!
Thursday, December 14 - Today is a very busy day in astronomical history. Tycho Brahe was born in 1546. Brahe was a pre-telescopic astronomer who established the first modern observatory in 1582 and gave Kepler his first job in the field. In 1962, Mariner 2 made a flyby of Venus and became the first successful interplanetary probe. And, in 1972, the last humans returned to Earth from the lunar surface. Eugene Cernan left the final boot print at Taurus-Littrow and said it was "the end of the beginning."
Tonight will be one of the most hauntingly beautiful and most mysterious displays of celestial fireworks all year - the Geminid meteor shower. First noted in 1862 by Robert Marsh and Prof. Alex Twining during independent studies, the Geminid stream was initially weak - producing no more than a few per hour. Over the last 150 years, it has grown in intensity. By 1877 astronomers realized a new annual shower was occurring with an hourly rate of about 14. At the turn of the century, the Geminids increased to an average of over 20, and by the 1930s, 40 to 70 per hour could be counted. Only eight years ago, observers recorded an outstanding 110 meteors per hour on a moonless night…and it is moonless again!
Why are the Geminids such a mystery? Most meteor showers are historically documented for hundreds of years, and are known to be the product of comets. When astronomers first began looking for the Geminids' parent comet, they found none. It wasn't until October 11, 1983 that Simon Green and John K. Davies, using data from NASA's Infrared Astronomical Satellite, detected an object that was confirmed the next night by Charles Kowal to match the Geminid meteoroid stream. But this was no comet - it was an asteroid…
Originally designated 1983TB, and later renamed 3200 Phaethon, this rocky solar system member has a highly elliptical orbit placing it within 0.15 AU of the Sun every year and half. But asteroids don't fragment like comets - or do they? Original thinking noted that Phaethon's orbit passes through the asteroid belt, and it may have collided with other asteroids causing rocky debris. This sounded accurate, but further study revealed the meteoroid "path" was associated with Phaethon nearing the Sun. The asteroid now behaves like a comet…
What exactly is this "thing?" We do know that 3200 Phaethon orbits like a comet, yet has the spectral signature of an asteroid. By studying photographs of meteor showers, scientists determined these meteors are denser than cometary debris - but not as dense as asteroid fragments. This leads science to believe Phaethon might be an extinct comet that gathered a thick layer of interplanetary dust during its travels, yet retains an icy nucleus. Until scientists are able to take physical samples of this "mystery," we may never fully understand what Phaethon is, but we can fully appreciate the annual display it produces!
Thanks to the wide path of the stream, observers around the world have an opportunity to enjoy the show. The traditional peak occurs tonight as Gemini appears around mid-evening and lasts through tomorrow morning. The radiant for the shower is near bright star Castor, but meteors can originate from many points in the sky. From 2:00 a.m. until dawn (when our local sky window is aimed directly into the stream) it may be possible to see one "shooting star" every 30 seconds.
Friday, December 15 - Today in 1970, Venera 7 made a soft landing on Venus - making it the first probe to successfully touch down on another planet.
Just after sunset, look to the southeast and land your eyes on Venus! The planet now shows a nearly full disk and is located some 110 million kilometers from Earth. The planet's bright globe will be difficult to resolve telescopically due to very low sky position. Try stacking colored filters to reduce the glare and reveal its gibbous shape.
Saturday, December 16 - Today we celebrate the birthday of Edward Emerson Barnard. Born in 1857 and raised by his mother during the American Civil War, E. E. Barnard began his career as an observational astronomer whose skill at the eyepiece led to the discovery of three comets by the age of 25. After a successful amateur career, Barnard studied mathematics at Vanderbilt University where he continued scanning the sky using the University's 6" refractor to discover eight more comets - and a galaxy. After graduation, he took professional employment at Lick observatory and again proved his talent for observation by discovering Jupiter's 5th moon Amalthea - something missed by numerous other very competent observers. Barnard later became one of the early pioneers of astrophotography which carried his powers of discovery well beyond the solar system!
To honor this celebrated name in astronomy, let's try some studies pioneered by Barnard - dark or obscuration nebulae. You might think them impossible to see, but that doesn't mean they can't be detected. Even casual observers of the Milky Way notice large dark rifts where the faint sheen of innumerable unresolved stars is lost to view. There's the key…obscuration nebulae are seen against the faint glow of more distant stars (or brighter nebulae) because they absorb visible light. Care to try for an obscuration nebula? Then let's do Barnard 150 in Cepheus. Look for a curved filament about a finger-width south of Eta Cephei. Or Barnard 163 - less than a degree south-southeast of the center of expansive open cluster IC 1396 south of Mu Cephei. You can always look for Barnard 169 - a set of thin curved lanes just northwest of magnitude 5.6 LZ Cephei.
Sunday, December 17 - Tonight we are going to challenge our observing eyes on a "stepping stone" series of 11th magnitude galaxies. Start at 3.7 magnitude Gamma Piscium, then shift a degree and a half northwest to locate 11.7 magnitude NGC 7541. Detectable in modest scopes, this highly tilted spiral will appear cigar shaped in larger instruments. From NGC 7541, head a little more than 2 degrees north-northwest to slightly brighter elliptical galaxy NGC 7562. This one will show a condensed core fading rapidly into space. Less than 2 degrees north-northwest of NGC 7562 lies a pair of close, magnitude 11.1 elliptical galaxies - NGC 7619 and NGC 7626. They are within 7 arc-minutes of each other and are virtual twins - slightly brighter versions of NGC 7562. Continuing north-northwest is the big scope challenge IC 1486, a small, 13th magnitude, football-shaped elliptical requiring high magnification to distinguish itself from a fuzzy star.
And if anyone asks you what you did tonight? Tell 'em you "went fishing!"
May all your journeys be at light speed… ~Tammy Plotner.
Filed under: What's Up
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