STARGAZING NOTES FOR MAY 1989 Gail S. Cleere 202/653-1541 The Planets MERCURY is visible low in the western sky at sunset early in the month. By May 23rd, however, this dried up prune of a planet reaches inferior conjunction (placing himself neatly between Earth and Sun) and cannot be seen. VENUS becomes visible at the end of the month, low in the western sky after sundown. The lovely lady is setting among the magnificent winter constellations. Look for her close by the great god Jupiter on May 22-23, at -3.9 magnitude (that's bright!) to Jupiter's -2.0. A pretty sight indeed on a warm spring evening. MARS is terrifically disappointed, having expected a visit from us this year. We have lost contact with both of the Soviet spacecraft that were due to land on Mars' 2 little moons. There seems to be no hope at this point that contact will be restored. Meanwhile, Mars consoles himself with a visit to the twins Castor and Pollux in the constellation Gemini. Look for the three of them well up in the western sky at sunset, setting together about 3 hours later. JUPITER continues to flirt with the stars of Taurus, passing 5 degrees above the red star Aldebaran (God's Eye, according to the Hebrews) on May 4th. Look for this low in the west just after sunset. Take one last look for the season at these fellows. By the end of the month, Jupiter and his pals are too close to the Sun to be seen, but by July will be back in morning skies. SATURN, URANUS and NEPTUNE manage to boot a couple of friends (Mars and Jupiter) off the western edge of the world at sundown, just as they get ready to rise themselves over the eastern edge of the horizon. Saturn remains among the stars of the teapot (Sagittarius), just where he's been for the last few years, and Uranus and Neptune trail right along with him. A waning gibbous Moon barges past the lot of them on the 23rd-24th. Neptune, meanwhile, gets ready for his close encounter from the Voyager 2 spacecraft, due to occur at 1 a.m. EDT on 25 August. Ten years ago, Voyager sailed past Jupiter. Eight years ago the spacecraft reached Saturn, and just three years ago visited Uranus. After the spacecraft's encounter with Neptune, Voyager 2 will join its twin Voyager 1 and float into the outer reaches of space. Last summer, Voyager's trajectory was corrected by NASA engineers, assisted by observational data supplied by the Naval Observatory. PLUTO does something of significance for a change, reaching opposition on May 4th. It means he'll rise in the east just as the Sun goes down, and remain in the nighttime sky until dawn. Haul out a decent sized telescope (and a decent sky chart) and see if you can spot him on his heavenly perch in Virgo. The Moon New Moon: 5 May Full Moon: 20 May First Quarter: 12 May Last Quarter: 28 May The month of May was once called Thrimilce by our pastoral Anglo-Saxon ancestors, as cows could be milked three times a day in May. The Full Moon of May is still called the Milk Moon because of this. The Indians of North America did not raise cows, however, and their names for this month's Full Moon were: Moon of the Shedding Ponies (Lakota Sioux), Corn Planting Moon (Algonquin), and Moon of the Time When the Horses Get Fat (Cheyenne). It's May! Mayday. The first of May is the great reckoning of the coming of Summer, and was once one of the most important of the year's festivals for our Anglo-Saxon ancestors. Today, the all-important flocks and herds were driven to their summer grazing pastures. Maypoles were erected. There was general carousing throughout the land. Perhaps the most vivid picture most of us have of what the day must have been like was shown in one memorable scene in the movie Camelot. Mayday was once a full-blown pagan festival called Beltane. For our ancestors, the customs and rituals on Mayday were plentifold. Young girls would rise early to wash away their freckles with Mayday's morning dew (thought to be especially powerful if gathered from ivy or from under an oak). The dew from new-made graves was gathered to cure gout, weak eyes and other ailments. Nine teams of nine married men (or 81 first-born sons) would go out to gather the wood from nine different trees and then light great bonfires from the hills around the township. The townfolk would then dance sunwise round the flames to invoke the gods of Summer to protect them and their flocks through Halloween, another cross-quarter day, falling six months hence. Throughout the countryside, however, the central custom was to spend much of the night out in the forests and fields to gather flowering branches and bring them home in triumph at sunrise. The pagan woodsprite, Robin Goodfellow, alias Puck, was believed to be about. It was what else went on in the forest that became a problem. The Puritans put an end to much of all of this by the mid-17th century. What's this got to do with astronomy? Precisely this: Mayday is a cross-quarter day -- falling midway between the solstices and equinoxes, the great hinges upon which the calendar year revolves. All of these dates, but especially the cross-quarter dates, were important to the early Celts and Anglo-Saxons. Today, the date and time of the equinoxes and solstices are mathematically determined by the U.S. Naval Observatory and England's Royal Greenwich Observatory. The Vernal Equinox is the fundamental reckoning point for all objects in the heavens. The cross-quarter days are not marked much today, and most have been entirely forgotten. Today, most of the men I know couldn't identify nine trees, let alone cut them down. But Mayday is still celebrated throughout Europe and in many towns in this country, although many of the more unusual ancient customs have been lost. Sailing Through a Comet's Path: Twice a year the Earth passes through the path of Halley's Comet. On the night of May 3-4, we will encounter small frozen particles spewn off the nucleus of this great Comet, which we call the Eta Aquarids Meteors. They will appear as shooting stars, emanating from Aquarius, a constellation which rises after midnight this time of year. In the hours just after midnight, when your location on the planet is at the leading edge of the Earth as it turns on its axis into the comet's path, watch the celestial diamonds left behind for us by Comet Halley. You may see about 20 per hour, maybe less, but possibly more, since the comet is still in the general vicinity. The ancient cosmic iceberg just crossed the orbital path of Saturn, outbound, last fall. Experience Astronomy... May 13th is Astronomy Day, celebrated nationwide at most observatories (check local papers). Here at the U.S. Naval Observatory, we plan to have you get acquainted with some greats from history who will get you acquainted with their favorite subject. The USNO will open from 10 am - 4 pm, all our telescopes will be open to the public, and joining the festivities will be Galileo, Newton, Einstein, Halley and Ptolemy, among others, who will explain what the Observatory does today. Bring your questions, the kids, and a picnic lunch (or get something from our cafeteria). Call for our press release and notice: 202/653-1541 (leave your name and address, or your FAX number). U.S. Naval Observatory to Build New High-PrecisionTelescope During the period 1989-1992, the Naval Observatory will design and build a unique high-precision telescope called an astrometric optical interferometer. This project is among the largest and most complex ever undertaken in the Naval Observatory's 160-year history. Routine astronomical observations should begin by 1993. An interferometer, simply stated, is several telescopes operated as one. In the case of the optical interferometer, the four light-gathering mirrors will be located at separate locations, but will act together as a unified system. The four mirrors will each be about 1.2 meters in diameter, and be located up to 40 meters apart. They will direct the light from the stars through evacuated underground pipes, into a large underground optics building which will house the most sensitive components of the interferometer: the delay lines, beam combiners, and electronic detection systems. Since its establishment in 1830, the Naval Observatory has continually conducted observation programs to determine the precise positions and motions of the Sun, Moon, planets, and stars. Historically this has been done (and continues to be done today) with transit circle telescopes -- single-lens instruments making a single observation at a time. The new telescope arrangement will make it possible to determine the exact positions of stars to an accuracy 10 times better than what we can determine today. The instrument can also provide new information on the diameters of stars and the configuration of close double-star systems. Once in operation, observations made with the new optical interferometer will provide a high-accuracy stellar reference frame for 21st century applications. The U.S.Naval Observatory is the authority in the United States for astronomical data required for timing, navigation, civil affairs, and legal purposes. Master Clock Time: (202) 653-1800 or 900-410-TIME ($0.50 - 1 minute) Earth & Sky Report on (202) 357-2000 This news release may be reproduced, with credit please, to the U.S. Naval Observatory. NAVOBSY WASH