StarWatch: Moravian College Astronomy

JUNE 2004

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Changing Venus: Venus first became prominent as it emerged from the back of the sun in early December 2003 as seen in this Dec. 7 photo, (upper left). By late March, Venus had moved to its greatest elongation west of the sun as seen in the March 27 image (upper right). The bottom picture, taken on May 28, shows Venus as it heads back to pass in front of the sun on June 8. Photography by Gary A. Becker…

And finally, the transit... Mark Balanda of Palmyra, PA took these photographs of Venus transiting the sun from Cabela's near Hamburg on June 8. The photo to right shows the famous black drop effect which made accurate transit timings so very difficult to make. More pictures and the full story will be found below.

406a JUNE 6-8, 2004: Venus Positioned for Transit: The Allentown School District’s StarWatch team, in coordination with Hawk Mountain and Cabela’s at Rt. 61, just north of Interstate 78, Exit 29, invites you to witness the planet Venus as she crosses the face of the sun for the first time in 121 years. The East Coast will be witness to the last two hours of the transit on Tuesday morning, June 8 from sunrise (5:30 a.m.) to 7:15 a.m. Our telescopes, equipped with solar filters or projection units, will be at Cabela’s in the back section of the RV parking area by 5:00 a.m. to catch the 5:30 rising sun. Cabela’s offers a nearly flawless eastern horizon and an abundance of parking. Yes, 5:30 a.m. is an ungodly hour to be conscious, but when Venus last transited the sun, we were illuminating our homes with kerosene and gas lamps and riding in steam-driven trains. Einstein, who would become the most influential human of the twentieth century according to Time magazine, was just learning to speak. The Venus transits of 1874 and 1882 allowed astronomers to calculate the Earth-sun distance known as the astronomical unit. I’ll address this topic in Tuesday’s StarWatch. If you cannot get to Cabela’s, you can view the Venus transit at your own favorite location with a good eastern horizon by purchasing commemorative Venus transit glasses at Dan’s Camera City, 1439 W. Fairmont St., Allentown—610-434-2313—for $2.50 per pair. All proceeds will benefit the ASD Planetarium. You can also use any of the solar eclipse glasses that you might have purchased years ago. A preliminary go/no go message will be posted at www.astronomy.org on Monday at 6 p.m., then updated at midnight, or call the ASD Planetarium at 484-765-5557 for the 6 p.m. message. Clear skies!

406b JUNE 9, 2004: The Black Dot on the Red Sun: Maybe it was just nervous knots in my stomach in anticipation of an event that I had known about for 30 years or perhaps it was just being up all night listening to my students who were just too pumped up to sleep, but when our caravan of StarWatch observers drove south, down the windy roads from Hawk Mountain to Cabela’s in Tilden Township, north of Hamburg for Tuesday’s Venus transit, I had a definite sinking feeling—dense fog. It surrounded us all the way along Route 61 even to the hilltop at Cabela’s. Everyone knew the routine. Car and van doors opened, and a silent brigade of people spilled onto the green, wet field carrying tripods and long tubes, moving about like a team of busy ants, assembling telescopes and aligning mounts. Within minutes our equipment became wet. We kept everything capped to keep the moisture out. The sky brightened with blue overhead, and suddenly there were people, dozens, then scores, and finally hundreds, looking in the same direction, watching the brightening sky against a wet, hazy horizon. I kept saying, “What a wonderful birthday gift this would be. How about it?” Suddenly an exuberant voice shouted, “I see the sun.” I looked through my scope. There was the black dot of Venus against the face of a deep, crimson sun. Old Sol grew a little brighter through the foggy sky, but still safe to view with the unfiltered eye, and suddenly we were all seeing the small dot of Venus over the sun, plain as the brightening day. Pessimism exploded into euphoria and smiles. When it was over and we were all packed and ready to leave, Mark Balanda of Palmyra, PA presented me with a box. Inside was a birthday cake in the shape of a red sun with a black dot. “Happy Birthday, Gary,” it said.

406c JUNE 10-12, 2004:   The Astronomical Unit and Venus
Tuesday’s transit of Venus highlighted one of astronomy’s rarest celestial events. Although this event was more for show, the two previous transits in 1882 and 1874 helped to establish a fundamental yardstick for solar system measurements called the astronomical unit (AU), the Earth-sun distance. The observations that helped to nail down this value needed precise timings of the moment when Venus was tangent internally to the solar disk, as well as accurate observer locations. The solution to knowing the AU’s value used geometry and the concept of ratios. We knew the relative proportions of the Earth-Venus distance and the Venus-sun distance. By watching Venus transit the sun from two known locations that were widely separated, it was possible to obtain the true distance in miles between the two different paths that Venus traversed across the solar disk. The angular separation between the Venus paths was a proportion of the total angular diameter of the sun. This allowed astronomers to calculate the true diameter of the sun in miles. Once astronomers had an accurate value for the sun’s diameter, they could ask, “How far away would we have to move the sun to see it as big as it appears to us in the sky?” That answer gave us the Earth-sun distance or the astronomical unit in miles. Knowing the AU gave scientists the ability to attach actual distances to the other members of our solar family, which before had only been known in relative units based on the AU. The observations and timings turned out to be excruciatingly difficult to make, but when the dust cleared 12 years after the 1882 transit, the AU was established at 92,797,000 miles, still smaller by 150,000 miles than the current value of 92,946,800 miles.

407    JUNE 13, 2004:   Summer Beckons
It has been a wonderful spring filled with interesting sky events and opportunities to observe the precision of the clockwork universe. We watched the planets gather in the evening sky during early spring and witnessed the final pageantry of Venus transiting across the face of the sun. Then there was Comet NEAT and the magic of its glowing gas tail sculpted by the sun’s magnetic field. So what happens now? Maybe it’s time to kick just back a little and catch our breath, to revel in the warmer spring nights, the lightning bugs adding their own spontaneous rhythm above the moist grass of our lawns and the beckoning summer stars. My favorite asterism of the season is the Great Summer Triangle low in the east at 10 p.m. Asterisms are not official constellations. In fact, the GST represents the brightest stars of three patterns: Vega of Lyra the Harp (brightest), Altair of Aquila the Eagle, and Deneb of Cygnus the Swan (faintest). As the clearer cooler nights of spring give way to the muggier evenings of summer, often these three luminaries will be the only ones that are visible, especially from more light-polluted locales. Observe from the pristine Rockies or Southwestern deserts, and your view will be radically different. Spanning the Great Summer Triangle and arching across the entire sky as the night deepens will be a hazy band of light, our Milky Way Galaxy. When I was in college, I remember one exceptionally transparent summer evening when I mistook the Milky Way for a cloudbank rolling in above some nearby trees. I actually contemplated putting away my gear until I examined the haze with binoculars and happily saw star clouds instead. Find an online map of the Great Summer Triangle at the URL below.

The Great Summer Triangle is a surefire indication that summer is upon us. Catch it low in the east at 10 p.m. If you are viewing from a rural location, expect to see the hazy star clouds of our Milky Way Galaxy also visible.

408    JUNE 20, 2004:   Rock Star
I remember orbiting the sun when I was very young and being pulled by this irresistible tug and coming down hard. There were rocks like me, all around and more rocks that fell on top of me. It was like being in a pressure cooker. I played a tiny part in the moon’s tumultuous birth, but the worst was yet to come. Heat and more heat—it felt like the sun. I melted and so did my friends. We mixed, partied, and froze again, slightly different than before. There was still the pressure. I knew I wasn’t alone. There were tons of other rocks squeezing me in, and I could still feel the heat. One day it happened, a rumble shaking the moon right down to its core. The rumor was that something big had struck—gouged a super huge basin. We all cracked up—yeah right! But the pressure did decrease, but not the heat. This time it came from radioactive decay. Gradually I melted and was on the move again, working up through those cracks, out onto the surface to cool and harden. I think I must have daydreamed for an eternity. The tedium seemed endless until one day I saw through my olivine eyes something coming—in bulky white—kneeling next to me, picking me up. Was I dying? I was put into a sack, taken to Earth where again people still mostly in white surrounded me. I finally was getting the attention I deserved. WACK! I was chipped, then smothered in acrylic. Suddenly, there were lights, cameras, and even beautiful women staring at ME! Overnight I had become a rock star! Still some thought me a lunatic, but most really liked me for myself. You can see my less fortunate friends still hanging tightly later this week in the west. My first home, the moon, will be full by July 2. I come from dark Serenitatis, a sea where there is no water.

409    JUNE 27, 2004:   Phoenix Reborn
Saturn, so prominent in our sky this past spring, has finally succumbed to the western glare of the setting sun. But like the Egyptian phoenix that was consumed by fire at death, only to rise in splendor from its ashes, Saturn’s demise is merely the prelude to more glorious days ahead. The robotic eyes of the Cassini-Huygens spacecraft are Saturn’s equivalent of the phoenix’s rebirth. A joint venture of the National Aeronautics and Space Administration (Cassini) and the European Space Agency (Huygens), the Cassini-Huygens mission has been underway since October 15, 1997 when it was launched from Florida’s Kennedy Space Center. Using a total of four gravity-assisted maneuvers from both Venus and the Earth, Cassini was literally slingshot from the inner solar system into Saturn’s realm. On July 1 it will begin orbiting the Ringed World on a four-year mission of discovery to understand better Saturn’s composition, weather patterns, icy ring structure, magnetic field, and 31 natural satellites. But there’s more. A 703-pound probe named Huygens will be released from Cassini on Christmas Day. Three weeks later on Jan. 14, 2005, Huygens will begin its two and one half hour parachute descent through the nitrogen rich atmosphere of Saturn’s largest moon, Titan. En route, the spacecraft will glean proprietary information about Titan’s atmospheric chemistry, density, pressure, and temperature. With a little luck, transmissions will continue for a few minutes after landing, giving scientists vital data about Titan’s surface conditions near the equator. Other Cassini highlights include close encounters with Saturn's moons, Rhea, Enceladus, Titan, Hyperion, Dione, and Iapetus. Already Cassini has imaged the renegade moon, Phoebe.