High Moon for Eclipse Watchers
MANY professional astronomers await the launch of the Hubble Space Telescope. Others design instruments with the latest electronic wizardry. In these days of high-tech stargazing, it's good to know there's still low-tech work for amateurs. Tomorrow's eclipse of the moon offers such an opportunity. It will be widely visible - weather permitting - throughout most of the Americas as well as parts of Western Europe and Western Africa. And amateur observers throughout this vast area are ready to glean all the useful data they can.
They will estimate the brightness and color of the moon when it is in Earth's shadow. This ranges from a very dark, almost invisible moon, to a bright, coppery-red or orange disk. The atmosphere scatters and refracts light into Earth's shadow. The more dust - generally volcanic dust - in the stratosphere, the darker the eclipse. Noting that there has been no dust-ejecting volcanic eruption since 1985, the astronomy magazine Sky & Telescope says, ``the betting is that the [eclipsed] moon will be bright.''
Some observers will note the precise time Earth's shadow touches various lunar craters. This will enable analysts to calculate the size of that shadow.
Observers will also record the exact instant when the moon moves in front of various stars - the technical term is ``occults'' the stars - and the instant when the stars reappear. The International Occultation Timing Association is coordinating these observations. They will help analysts accurately delineate the moon's profile.
These observations continue a record of lunar eclipses that has been kept by one human culture or another for thousands of years. It is a record that yields useful scientific information today.
For example, records of solar eclipses help scientists estimate changes in Earth's rotation if they can accurately date those eclipses. Last June, Dr. Kevin D. Pang of the National Aeronautics and Space Administration's Jet Propulsion Laboratory reported that he and his associates had found a record of an ancient solar eclipse observed at Anyang, China. The record is engraved on an old tortoise shell with no exact date. It could refer either to an eclipse in 1302 BC or to one in 1250 BC. Contemporary lunar eclipse records showed that both the lunar and solar eclipse observations were made before 1250 BC. Pang and his co-workers estimate the day was 0.047 seconds shorter in 1302 BC than it is now for the solar eclipse to have been seen at Anyang at that time.
You don't have to be a serious observer to appreciate the Oct. 16-17 lunar eclipse. It will be easy to watch if the sky is clear. Over eastern North America, the moon will be up when the eclipse starts. Over western regions, it will rise partly obscured. The whole show will occur with the moon high in the sky over South America. Western Europe and Western Africa will only see part of the eclipse in the early morning.
This is a long-playing spectacle. Totality lasts an hour and 36 minutes. Enjoy!