Satgen365 Comets and Meteors by GM4IHJ 23rd March 96 For the past 10 days and nights, the skies over Scotland have had the consistency and colour of cold congealed mushroom soup. By the time this bulletin is posted on Friday 22nd, Comet Hyakutake C/1996 B2 may be a naked eye object in the eastern night sky as it passes 8 degrees away from the bright star Arcturus. During April it will fade by a magnitude or so, before being lost as it passes perihelion closest approach to the Sun. Thereafter emerging as a Southern Hemisphere object in May. Hopefully we will get one clear night , to see it at this very close encounter only 1 million miles from earth. Then Hyakutake will not be back again for 10000 years. Which makes it unlikely that it will give us that other gift of the comets - the trail of microscopic dust which provides us with our annual or twice annual meteor showers as the earths orbit takes it across the dusty path of the long gone comet. Regular visitor comet Halley is one such provider of a double meteor shower. We call the one in October , peaking on the 20th, the Orionids, because the incadescent trails of the meteors as they hit the atmosphere appear to come from the stellar constellation of Orion. The other shower from Halley which we call the Aquarids reaches its peak on 4th May every year. Returning as it does every 76 years, Halley has built up an almost regular and complete band of dusty debris all around its orbit track . But Halley was caught long ago in the gravity field of one of the big gas giant planets which has trapped it in this short period orbit. By contrast Hyakutake has not yet been caught so its orbital visits to the inner solar system have been too rare to build up a dust trail good enough to give us an annual meteor shower. Most Astromers ignore or are unaware of the wealth of detail that radio observation of meteor showers can provide. But radio/radar operation has its pitfalls. Indeed a recent letter to Sky and Telescope astronomy magazine gave a good account of this when it contrasted a radar report from a professional observer against a visual report from another observer seeing the same super shower provided by the November Leonids in 1996 ( next due 1998 or 1999). The observer saw nearly 500,000 meteor/hr but the radar peaked at only 15000/hr. This result may not come as a surprise to regular radio meteor scatter users. It is frequently the case in major showers that radio echoes overlap so completely that counting is impossible. There is a way of avoiding this problem however, by using two radio systems of different sensitivity. The classic example of this is using a strong European TV signal on say 48.421 Mhz and receiving it on both a narrow band audio operated counter whilst simultaneously looking at the signal echoes on television , counting pictures seen on this much wider bandwidth less sensitive system . In showers like the Leonids or the January Quadrantids, this TV picture count method is often the only way to judge where and when the shower peak occured. During Quadrantids in the 1980s audio echoes were continuous for 40 minutes or more rendering counting impossible but TV counts gave a clear picture of the timing of shower peak and allowed a useful estimate of zenith hour rate.