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JULY 4, 1999: Meteors, Meteoroids, and Meteorites
- There is a type of celestial fireworks that has been witnessed by humans since the dawn of their existence. They are called meteors, or more commonly, shooting stars. Whenever you observe a shooting star piercing rapidly through the black night sky, you are most likely witnessing the final act in the existence of an extremely small of chunk of debris spewed from the nucleus of a comet. The flash of light is created by air molecules which are set aglow as the meteoroid slams into our protective atmosphere. Speeds range between 7 and 45 miles per second. If the air is unable to stop or consume the meteoroid completely, a piece of it will reach the Earth’s surface, now to be known as a meteorite. Meteor, meteoroid, and meteorite are three of the most butchered words in astronomy. Part of the problem stems from a lack of commitment in the professional community. Astronomers, most of whom are educators, seem to use the words interchangeably. Of course, if an astronomer (scientist) says it, then it must be true. Incorrectly use a few words for which most of us do not have precise definitions, and misconceptions rapidly change into gospel. The other problem with these terms, stems from Meteor Crater, a nearly one mile in diameter hole in the Earth just off I-40 west of Winslow, Arizona. It was formed by a 100 yard nickel-iron METEORITE which struck our planet about 49,000 years ago. Had this event occurred in modern times, it is believed that the "dead zone" for humans would have reached to a radius of 40 miles from the center of impact. Make no mistake; Meteor Crater is very spectacular, and well worth the visit, but it was made by a meteorite.
JULY 11, 1999: Venus' Motions
- Where has Venus gone? The evening star of the west, which was so high in the sky just over a month ago, has now become a horizon hugger after darkness. Venus emerged from the glare of the sun during mid-January and became more and more prominent during late winter and most of the spring. But then in June, it became very obvious that Venus was beginning to lose its grip at being champion of the early evening sky. Although it has brightened slightly, each night has brought it just a little closer to the western horizon. What has been happening? If we imagined looking down on Venus and the rest of our solar family from above the sun, we would see Venus orbiting in a counterclockwise direction. We’d also realize after a while that the solar system was pretty flat and that the planets revolved around the sun very close to the Earth’s orbital plane. Relocating ourselves in the plane of the solar system would put us back on the Earth. Since Mercury and Venus are sunward, they seem to pivot to the right and left of the sun as they orbit. When Venus appears to the left (east) of the sun, it is in our evening sky. Venus is moving from behind the sun towards us. Venus reached its greatest eastern elongation on June 11. Since then, Venus has continued to approach the Earth while moving towards inferior conjunction with the sun. Venus is between the Earth and the sun on Friday, August 20, then quickly assumes prominence in the morning sky. Venus’ change from the evening to the morning "star" occurs rapidly because the planet is close to Earth which gives it the illusion of moving faster. Venus can be found low in the west near the star Regulus this week. The moon will join the pair on Friday.
JULY 18, 1999: August 11 Partial Solar Eclipse--Part 1
- There are two exciting astronomical events which will be visible over Lehigh Valley skies in August: a partial solar eclipse and the annual Perseid meteor shower. Ironically, both occur within 24 hours of each other on the mornings of the 11 and 12 of August. To say the least, the solar eclipse of August 11 will be a strange one for us, not conducive to a good night’s rest. Globally, the moon will completely hide the sun just south of Nova Scotia, across the north Atlantic, SW England, northern France, Germany, Austria, Romania, the Black Sea, Iraq, Iran, Pakistan, and India. For observers in the mid-Atlantic states and New England, sunrise might appear just a little strange, especially if it’s hazy, for the sun will be partially eclipsed by the moon as it becomes visible above the horizon. For Allentown, the maximum eclipse magnitude will be 36 percent at sunrise, which occurs at 6:08 a.m. EDT. This means that 36 percent of the moon’s diameter will be overlapping the sun’s diameter when it rises. As the sun gains altitude, the moon will slip off its face, leaving the sun a scant 3 degrees above the horizon when it all ends at 6:27 a.m., EDT. The low solar altitude will make it paramount for observers to seek an unobstructed eastern horizon. If you’ll be anywhere northward of the Jersey shore and along the coast, you will experience much more. Coastal Maine catches a nearly total eclipse at sunrise with a magnitude of about 90 percent, while Halifax, Nova Scotia sees over 93 percent at 5:34 a.m., ADT. At Halifax, greatest obscuration occurs 23 minutes after sunrise. More next week, or read ahead at the
JULY 25, 1999: August 11 Partial Solar Eclipse--Part 2
The partial solar eclipse of August 11 (see last week’s StarWatch) is sure to pose some observational dilemmas. The sun will rise at 6:08 a.m. EDT with 36 percent of its diameter obscured by the moon. The brightness of the sun and other objects near the horizon are substantially reduced by the Earth’s atmosphere. The use of standard solar filters may attenuate too much light when the sun is on the horizon, leaving it invisible. Even so, I can only recommend these types of filtration systems as completely safe. You can purchase Eclipser aluminized Mylar sunshades, at $1.95/unit from Dan’s Camera City--610-434-2313. Ask for Tim or Richard. Also, a #14 shade welder’s glass is completely safe and can be obtained or ordered from any welding supply company. In addition, to the #14 shade, or Mylar filter, I would also recommend purchasing a #12 shade welder’s filter. Normally a #12 shade presents an image of the sun which is too bright for comfortable viewing. It does, however, reduce the sun’s ultraviolet and infrared radiation to safe levels. The #12 shade filter may afford the best compromise for maintaining maximum safety while allowing the reduced brightness of the rising sun to be more easily seen. Remember, NEVER, use sunglasses of any kind, colored cellophane, colored filters, neutral density filters (from photo stores), polarizing filters, color film negatives, chromogenic (silverless) b/w film negatives, or glass smoked by the soot from a candle flame. The web address below will provide full details regarding the observations of partial solar eclipses.