A winter wonderland ... look up! Wishing you knew what star you wished upon? The cold, clear light of night is the time to find out

One of the great viewing opportunities this winter takes place next Friday and Saturday nights, when the Amherst Area Amateur Astronomers Association (“the 5As’’) holds a rare winter observing program at Wilder Observatory on the Amherst College campus. The occasion is the Mars opposition: when the sun and Mars are on exactly opposite sides of Earth, an event that happens roughly every 26 months. The planet will be visible from sunset to sunrise. It won’t be this bright again for a few years.

The Wilder telescope was fabricated in 1903 by legendary telescope makers Alvan Clark & Sons of Cambridge. Its 18-inch front lens makes it one of the more powerful refracting telescopes still in use, and in 1907 the massive instrument was shipped to the high desert in Chile to make some of the first detailed photographs of Mars during that opposition. (It was immediately returned to its McKim, Mead, and White observatory.) The formidable telescope still employs its original clockwork mechanism. Tom Whitney, president of the 5As, says the 18-inch Alvan Clark is the telescope equivalent of a Stradivarius violin. “Everyone wants to come to the recital played on a Stradivarius.’’

Other vintage Alvan Clark instruments are operating elsewhere in New England. A 7.5-inch Clark telescope was installed at the Maria Mitchell Association’s Loines Observatory on Nantucket in 1913. In winter, the observatory opens to the public on the Friday and Saturday nights closest to the first quarter moon. The timing presents strong sideways shadows on the moon, providing crisp images of lunar features, including the Mitchell crater named for the pioneering Nantucket astronomer (1818-89). The guide scope mounted on the side of the Clark instrument is fitted with the lens from Mitchell’s own 1859 Clark telescope.