| Date: Jul 12 2001 18:46:42 EDT Subject: Martian Chronicles, July 2001, Part 2 of 2 ================================================== MARTIAN CHRONICLES - PART 2 OF 2 Newsletter of the Museum Astronomical Resource Society Volume 17, Number 7 - July 2001 ================================================== CONTENTS ================================================== - Biography: Hipparchus - Constellation of the Month: Hercules - Celestial Almanac - Meteor Showers - This Month in History - Publication Information - Newsletter Edition Details - Club Information ================================================== BIOGRAPHY by James M. Thomas ================================================== Hipparchus Born about 190 BC in Nicaea, Bithynia, died after 127 BC, possibly in Rhodes. (Pronounced "hi - PAR - kus") Hipparchus was a Greek astronomer and mathematician who discovered the precession of the equinoxes, determined the lengths of the four seasons, calculated the length of the year to within 6.5 minutes, compiled the first known star catalog, and made an early formulation of trigonometry. He was probably the greatest observational astronomer of ancient times. Sometimes referenced as Hipparchus of Nicaea or Hipparchus of Rhodes, his name was also spelled Hipparchos. Little is known of Hipparchus's life and the only book of his to survive is a commentary he made on the work of Greek poet Aratus (about 310 BC - about 240 BC). Most contemporary knowledge of Hipparchus is contained in the writings of the Greek geographer and historian Strabo of Amaseia (64/63 BC - about AD 23) and in the great astronomical compendium 'Almagest' by Greek astronomer Ptolemy (about AD100 - about 170). Ptolemy often quotes Hipparchus, and it is obvious that he thought highly of him; in fact, because of the slow progress of early science, Ptolemy speaks of Hipparchus with the respect due a distinguished contemporary, although almost three centuries separated the the two. It is often difficult to know which of them is due proper credit for their bodies of work. Hipparchus made his observations from Bithynia, at Rhodes, where he spent much of his later life, and also, it seems, at Alexandria. The year 127 BC is usually cited as the last date known for his actual work. French astronomer Jean-Baptiste-Joseph Delembre (1749-1822) clearly demonstrated that some observations of Hipparchus on the star Eta Canis Majoris ("Aludra") could well have been carried out in that year. (He used the star, then at 90° of right ascension, for convenience in astronomical reckoning.) In all his work Hipparchus showed a clear mind and a dislike for unnecessarily complex hypotheses. He rejected not only all astrological teaching but also the heliocentric (Sun-centered) views of the universe that seem to have been proposed, according to Archimedes (about 287-212 BC), by Aristarchus of Samos (flourished about 270 BC) and that were revived by Seleucus the Babylonian, a contemporary of Hipparchus. With respect, it is important to note that strong arguments had been advanced against the idea that the Earth moved, and the general climate of opinion had never been favorable to persue the earlier theories of Aristarchus. Beyond that, much work had been done to explain most of the irregularities observed in the motions of the Sun, Moon and planets when considered within a geocentric (Earth-centered) universe. The work involved the use of a system of movable eccentrics and a system of epicycles and deferents. It was based on the erroneous belief that all celestial movement is regular and circular, or at least that it is best described in terms of a system of regular motion in circles. In the system of movable eccentrics, the centers of the supposed orbits of bodies around the Earth were themselves revolving around the Earth. In the other system, epicycles were small circles theoretically imposed on the great circular orbital paths, called deferents. The epicycle-deferent mechanism was used along with the movable eccentric mechanism in Ptolemy's late version of the geocentric system. It was this Ptolemaic geocentric system that was handed down to western European science, but it must be remembered that the views of Hipparchus had a profound influence on Ptolemy, as he himself acknowledged. It was not until the 15th century that regular observations over very long periods showed the geocentric hypothesis to be too complex to be acceptable and Copernicus proposed that the Sun is the center of the universe. We know few details about the instruments that Hipparchus used. It seems likely that he observed with the devices common in his day, although Ptolemy credits him with the invention of an improved type of theodolite with which to measure angles. Hipparchus is best known for his discovery of the precessional movement of the equinoxes; i.e., the changing of the measured positions of the stars resulting from the movement of the points of intersection of the ecliptic (the plane of the Earth's orbit) and of the celestial equator (the great circle formed in the sky by the projection outward of the Earth's equator). It appears that Hipparchus wrote a work with the phrase "precession of the equinoxes" in the title. The term is still in current use, although the phenomenon is more usually referred to merely as "precession." This notable discovery was the result of painstaking observations worked upon by an acute mind. Hipparchus observed the positions of the stars and then compared his results with those of Timocharis of Alexandria about 150 years earlier and with even earlier observations made in Babylonia. He discovered that the celestial longitudes were different and that this difference was of a magnitude exceeding that attributable to errors of observation. He therefore proposed precession to account for the size of the difference and he gave a value of 45 or 46 seconds of arc for the annual changes. This is very close to the figure of 50.26 accepted today and is a value far superior to the 36 that Ptolemy obtained. The discovery of precession enabled Hipparchus to obtain more nearly correct values for the tropical year (the period of the Sun's apparent revolution from an equinox to the same equinox again), and also for the sidereal year (the period of the Sun's apparent revolution from a fixed star to the same fixed star). Again he was extremely accurate, so that his value for the tropical year was too large by only 6 1/2 minutes. Observations of star positions measured in terms of celestial latitude and longitude, as was customary in ancient times, were carried out by Hipparchus and entered in a catalogthe first star catalog ever to be completed. Hipparchus measured the stellar positions with greater accuracy than any observer before him, and his observations were of use to Ptolemy and even later to Edmond Halley. To catalog the stars was thought by some of Hipparchus' contemporaries to be an impiety, but he persevered. Hipparchus had been stimulated in 134 BC by observing a "new star." Concluding that such a phenomenon indicated a lack of permanency in the number of "fixed" stars, he determined to catalog them, and no criticism was able to deflect him from his original purpose. Hipparchus' catalog, completed in 129 BC, listed about 850 stars (not 1,080 as is often stated), the apparent brightnesses of the stars were specified by a system of six magnitudes similar to that used today. For its time, the catalog was a monumental achievement. Hipparchus also attacked the problem of the relative size of the Sun and Moon and their distance from the Earth. It had long been appreciated that the apparent diameter of each was the same, and various astronomers had attempted to measure the ratio of size and distance of the two bodies. Eudoxus obtained a value of 9:1, Phidias (father of Archimedes) 12:1, Archimedes himself 30:1; while Aristarchus believed 20:1 to be correct. The present-day value is, approximately, 393:1. Hipparchus followed the method used by Aristarchus, a procedure that depends upon measuring the breadth of the Earth's shadow at the distance of the Moon (the measurement being made by timing the transit of the shadow across the Moon's disk during a lunar eclipse). This method really gives the parallax (the apparent change in the position of a celestial body when observed from two different directions), and thus the distance, of the Moon, the parallax for the Sun being too small to give a significant result; moreover the accuracy obtainable for the distance even of the Moon is poor. Dissatisfied with his results, Hipparchus attempted to find the limits within which the solar parallax must lie for observations and calculations of a solar eclipse to agree; he hoped that differences between solar and lunar parallax might thus also be revealed. He obtained no satisfactory result from his efforts, however, and concluded that the solar parallax was probably negligible. At least he appreciated that the distance of the Sun was very great. ================================================== CONSTELLATION OF THE MONTH by Craig MacDougal ================================================== Hercules If the afternoon thunderstorms have cleared out by 9:30 at night, then go out to get a look at our constellation for July. Face toward the east, and look most of the way up to zenith. There you will find a square made up of 2nd and 3rd magnitude stars. This square covers an area of the sky a bit smaller than your fist at arms length, and it's noticeably "squashed" on the right end. This "squashed square" (also known as the "keystone") is the key part of that legendary strong man of old: HERCULES (HER-q-lees). The keystone is generally considered to be his torso, or thereabouts. His head is generally considered to be off to the right of the keystone, and he's usually shown facing east. So you can imagine our strong man running full tilt back toward the horizon with the pelt of Leo on his back. (Remember Leo?) The story of Hercules is a long one that has been told in a variety of forms for thousands of years. His mother was Alcmene, the most beautiful and wise of the mortal women. His father was Zeus. (It's beginning to seem like half of the characters portrayed in the sky were fathered by Zeus.) Zeus visited Alcmene disguised as her husband. (Visiting beautiful women while in disguise was apparently a hobby of Zeus.) Anyway, Zeus also arranged for the infant to drink some of his wife's (Hera) milk. Having drunk the milk of a goddess, Hercules was now immortal. Hera was quite annoyed over the entire situation. She could not kill Hercules, but she vowed to make his life very miserable. Hera made Hercules temporarily insane at one point, and this caused him to kill his family. When he came to himself, he was of course remorseful and asked the Oracle at Delphi how he might atone for this. The Oracle's instructions were to serve the king of Mycenae for twelve years. The king gave him a set of tasks that are known as the Labors of Heracles. (Heracles is the original form of the name. The version we know is Greek.) The first task was to kill a certain invincible lion. (Sound familiar yet?) He also killed a multi-headed monster, which became the constellation Hydra. While he was battling Hydra, a crab came out of the rocks and started going after Hercules' ankles. This didn't last long, since Hercules simply stepped on it between swings of his sword. For this short scene, the crab gets billing in the sky as the constellation Cancer. (I guess he had connections with Zeus, or something.) Anyway, Hercules completes the original ten Labors. The king however, points out that Hercules had help on one of them, and got greedy on another. So he gives him two more, expecting to do him in for sure this time. Hercules cheerfully dispatches a dragon (Draco), and rather than kill the three-headed watchdog of the underworld, dragged him back to the king. The king was surprised to see Hercules, and more surprised to be staring at this none-too-happy watchdog that Hercules had (for now) a firm grip on. The king wisely proclaimed that Hercules was a free man, and graciously suggested that he take his "puppy" outside before he let go of it. (Whew!) Let's turn back to the keystone, for about a third of the way from the upper left corner, to the upper right corner, is one of the glories of the heavens. Check this spot with binoculars, and you will find a fuzzy spot. This is M13, the great Hercules globular cluster. Now you have seen with your own eyeballs this grand collection of many thousands of stars that adorns the pages of every book on astronomy that I know. ================================================== CELESTIAL ALMANAC by James M. Thomas ================================================== MOON PHASES: Full Moon - July 5, 11:04AM EDT Last Qtr. - July 13, 2:45PM EDT New Moon - July 20, 3:44PM EDT First Qtr. - July 27, 6:08AM EDT MOON APOGEE AND PERIGEE: Apogee - July 9, 7:23AM EDT, 252,007 mi (405,566 km) from Earth Perigee - July 21, 4:46PM EDT, 223,089 mi (359,027 km) from Earth PLANETS: MERCURY - (mag. 1.7 to -0.2), dist. 63.4 - 90.0 mill. mi (120.0 - 14.5 mill. km); bright in the morning sky; moving through constellations Orion and Gemini toward Cancer VENUS - (mag. -4.1), dist. 92.1 mill. mi (148.2 mill. km); rising just before dawn; in constellation Taurus MARS - (mag. -2.2 to -1.5), dist. 42.4 - 50.7 mill. mi (68.2 - 81.6 mill. km); in constellation Scorpius near the star Antares JUPITER - (mag. -1.9), dist. 560.8 mill. mi (902.5 mill. km); in constellation Orion SATURN - (mag. +0.2), dist. 911.5 mill. mi (1,466.9 mill. km); in constellation Taurus URANUS - (mag. +5.7), dist. 1,774.4 mill. mi (2,855.6 mill. km); in constellation Capricornus NEPTUNE - (mag. +7.8), dist. 2,705.2 mill. mi (4,353.6 mill. km); in constellation Capricornus PLUTO - (mag. +13.8), dist. 2,752.2 mill. mi (4,429.2 mill. km); in constellation Ophiuchus EVENTS: July 1 - Comet P/Kowal-Mrkos (2000 ET90) Perihelion (2.454 AU) July 3 - Moon is 6° north of Mars, 6AM EDT July 4 - Earth is at aphelion (94.5 million miles from the Sun), 10AM EDT; Comet P/1999 DN3 (Korlevic-Juric) closest approach to Earth (3.788 AU) July 5 - Partial lunar eclipse July 6 - Comet Schwassmann-Wachmann 1 closest approach to Earth (4.919 AU) July 7 - Moon is 3° south of Neptune, 10AM EDT; Minor planet (asteroid) Ceres at opposition (mag. 7.3 in constellation Sagittarius), 3PM EDT July 8 - Moon is 3° south of Uranus, 6PM EDT July 9 - Mercury at greatest western elongation (21°), 1PM EDT July 12 - Mercury is 1.9° south of Jupiter (conjunction), 6PM EDT July 13 - Saturn is 4° north of the star Aldebaran, 4AM EDT July 14 - Venus is 3° north of the star Aldebaran, 9PM EDT July 15 - Venus is 0.7° south of Saturn (conjunction), 1AM EDT July 16 - Asteroid 2000 ET70 Near-Earth Flyby (0.330 AU) July 17 - Moon is 0.6° south of Saturn, 9AM EDT; Moon is 0.3° north of Venus, 2PM EDT July 18 - Moon is 0.2° south of Jupiter, 8PM EDT July 19 - Moon is 1.0° north of Mercury, 9AM EDT; Mars is stationary, 7PM EDT; Comet Tuttle-Giacobini-Kresak closest approach to Earth (1.520 AU); Comet Brooks 2 perihelion (1.835 AU) July 20 - Asteroid 2000 WN63 Near-Earth Flyby (0.324 AU) July 22 - Asteroid 17511 (1992 QN) Near-Earth Flyby (0.296 AU) July 23 - Asteroid 1995 OO Near-Earth Flyby (0.339 AU) July 26 - Asteroid 2000 PH5 Near-Earth Flyby (0.012 AU) July 27 - Mercury is 6° south of the star Pollux, 11AM EDT July 28 - Peak of Southern Delta Aquarid meteor shower July 29 - Comet C/2000 CT54 (LINEAR) closest approach to Earth (2.606 AU); Asteroid 1997 AQ18 Near-Earth Flyby (0.381 AU) July 30 - Neptune is at opposition, 8AM EDT; Moon is 6° north of Mars, 10AM EDT; July 30 - Asteroid 1999 YA Near-Mars Flyby (0.067 AU) ================================================== METEOR SHOWERS by James M. Thomas ================================================== Delta Aquarid Meteor Shower This minor shower peaks on July 27/28 and has a maximum of 30-40 meteors per hour. The orbit of the meteor material is small, highly eccentric, with its perihelion very close to the Sun. The radiant of the shower is near the star delta Aquarii (Scheat) in the constellation Aquarius. There are also two showers that peak in August with activity beginning in late July: Alpha-Capricornid Meteor Shower This shower is caused by Periodic Comet Honda-Mrkos-Pajdusakova. Meteors from this shower may be visible from July 15 through Aug. 25 with the peak on Aug. 2/3. The meteor hourly rate may be about 8. The meteors will appear to originate from a point in the constellation of Capricornus (RA 20 hrs 36 min, Dec -10°). Perseid Meteor Shower This shower is caused by Periodic Comet Swift-Tuttle, discovered on July 16, 1862 by Lewis Swift and then independently discovered three days later by Horace Tuttle. Meteors from this shower may be visible from July 25 through Aug. 21 with the peak on Aug.11/12. The meteor hourly rate may be about 75. The meteors will appear to originate from a point in the constellation of Perseus (RA 03 hrs 04 min, Dec +58°). Observing Meteors Meteors are best viewed from a dark-sky location. Observers in for the duration of the evening, or at least for several hours, should bring along a few things: a sleeping bag or blankets for warmth, a recliner or lawn chair, a hot beverage to help cut the chill, and binoculars to view the smoke trails of just-past meteors. ================================================== THIS MONTH IN HISTORY by James M. Thomas ================================================== July 24, 1950 - A U.S. Army team from the Ordnance Proving Grounds at White Sands, New Mexico, conducted the first rocket launch from Cape Canaveral, Florida. The rocket was called Bumper 8, a modified German V-2 missile with a WAC (Without Any Control) Corporal missile for a second stage. It achieved an altitude of 16 kilometers (10 miles). For the launch, Army technicians employed a painter's scaffold as a gantry to service the rocket before launch, and the control center was a converted tarpaper bathhouse surrounded by sandbags. July 21, 1961 - A Redstone rocket launched U.S. astronaut Virgil I. "Guss" Grissom in the Mercury 4 spacecraft, Libert Bell 7. This was the second U.S. sub-orbital space flight, and very similar to the flight of Alan B. Shepard Jr. a month earlier. It lasted 15 minutes, with a trajectory that took Grissom over the Atlantic Ocean where the spacecraft parachuted into the water. Grissom was recovered by helicopter from the ocean after leaving the spacecraft. Unfortunately, his spacecraft, Liberty Bell 7, sank and was lost until its recovery by a Discovery Channel-sponsored expedition early in 1999. (40th Anniversary) July 28, 1964 - The U.S. spacecraft Ranger 7 was launched. Ranger 7 became the first U.S. spacecraft to impact on the Moon. It returned a series of photos and other data. July 14, 1965 - The U.S. spacecraft Mariner 4 (launched November 28, 1964) reached the planet Mars and flew by on the far side of the planet. Mariner 4 transmitted back 22 televsion pictures of the cratered Martian surface from distance as close as 9,846 kilometers (6,118 miles). July 18, 1966 - John Young and Michael Collins were launched into Earth orbit aboard Gemini 10. They performed the first U.S. docking maneuver, using an Agena target vehicle. They returned safely to Earth on July 21. (35th Anniversary) July 16, 1969 - Neil Armstrong, Edwin "Buzz" Aldrin and Michael Collins were launched in Apollo 11. Armstrong and Aldrin, aboard the Lunar Module Eagle, landed on the lunar surface on July 20. Armstrong, and then Aldrin, became the first men to walk on the moon. They spent a total of 21 hours, 36 minutes and 21 seconds on the lunar surface, and collected 48.5 pounds of soil and rock samples. They returned to the lunar orbit, docked with Collins in the Command-Service module, and returned safely to Earth on July 24. July 15, 1975 - Aleksei A. Leonov and Valery N. Kubasov were launched in Soyuz 19. That same day Vance Brand, Thomas P. Stafford and Donald K. "Deke" Slayton were launched in an Apollo spacecraft . Both launches were part of a U.S.-U.S.S.R. joint flight. The spacecraft docked on July 17. The crews conducted experiments, shared meals, and held a joint news conference. Soyuz 19 returned to Earth on July 21 and the Apollo crew returned on July 24. July 20, 1976 - The Viking 1 spacecraft landed on Mars. Originally scheduled for a July 4th landing, in time for the U.S. bicentennial, the craft performed scientific experiments and transmitted images back to Earth for 6-1/2 years. (25th Anniversary) July 4, 1996 - The Mars Pathfinder spacecraft, launched Dec. 4, 1996, landed on the Martian surface at 1:08pm EST. The following day the Lander was renamed Carl Sagan Memorial Station. On July 6th the Sojourner rover was released to begin its exploration of the Martian surface. The mission performed measurements of the Martian climate, soil composition, and send back thousands of surface images. ================================================== PUBLICATION INFORMATION ================================================== Martian Chronicles is published monthly by the Museum Astronomical Resource Society (also known as the MARS Astronomy Club) to provide club news and other items of interest to its members. MARS is sponsored by the Museum of Science and Industry (MOSI), Tampa, Florida. Annual club membership dues are $12.00, which may be paid to any officer at club-sponsored events or mailed to the "Membership Renewal Address" listed below. Make checks payable to Frances Ferguson, our club treasurer. Newsletters are available to nonmembers by requesting a complimentary trial issue. Please send all inquiries, comments and newsletter contributions to the address below. The deadline for submitted contributions is the 15th of the month prior to the next issue. Contributions may be delayed in publication due to available space. NEWSLETTER EDITION DETAILS Martian Chronicles, July 2001, Vol. 17, No. 7 Editor: Jimmy Thomas Contributors: Craig MacDougal Circulation for this issue: Total: 98+ Membership - mail: 39, on-line: 8 Courtesy - 10, on-line: E-mail: 63 Membership Renewal Address: M.A.R.S. c/o Frances Ferguson 1522 W. River Lane Tampa, FL 33603 ================================================== CLUB INFORMATION ================================================== MUSEUM ASTRONOMICAL RESOURCE SOCIETY President - Jimmy Thomas, 813-888-7187, MARSAstro@aol.com Treasurer - Frances Ferguson, 813-238-8299, faf2@juno.com Secretary - Mark Dillenbeck, 813-685-3458, MDStarman@aol.com MOSI Contact - Craig MacDougal, 813-933-9617, MACDOUC@prodigy.net Current Membership: 52 Mailing address: 8712 Cobbler Place, Tampa, FL 33615 Web site: http://members.aol.com/MARSAstro E-mail: MARSAstro@aol.com ================================================== END MARTIAN CHRONICLES, PART 2 OF 2 ================================================== | |
|
