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December Skies 2018

Chart of area around Triangulum.
Chart of the area surrounding the constellations Andromeda, Triangulum, and Aries, as seen from Denver in mid-December at 9:00 PM, viewing just south of the zenith (nearly “straight up”). Telrad circles are shown centered on 6 Trianguli (6 Tri), one of this month’s targets. As an aid to finding 6 Tri, note how the circles center on the imaginary line running from Almach to Beta Tri, and how the outermost circle touches another imaginary line running between Gamma and Alpha Tri. –Object positions, constellation and meridian lines charted in SkySafari, and then enhanced. (Tap on image above for larger version.)

The Solar System

Mercury ended November lost in the solar glare, but as it sweeps rapidly through its orbit, it will become increasingly visible as a pre-dawn target. After about the first week of December, the planet will sit almost 10° above the southeastern horizon at 6:30 AM, roughly 40 minutes before dawn. (By then, it will look like a fat crescent in telescopic views.) A week later, Mercury reaches its widest angle, as we see it, from the Sun (known as “greatest elongation”), and sits slightly higher at the same hour, brightening by about a half-magnitude as well. After that, the planet will appear closer to the Sun each day. Look for a close conjunction with Jupiter on the morning of the 21st, when the two planets will lie within a degree of each other.

Late-November views of Venus were spectacular, even with the naked eye—the planet’s sheer brilliance in a dark sky made a 5:30 AM rise worthwhile. (Venus was so bright, it made it hard to recognize a nearby, seemingly wan star for what it really was: 1st‑magnitude Spica.)

Happily, the views continue in December—though the planet’s brightness diminishes slightly and the disk appears a bit smaller, it still presents a terrific target, Continue reading “December Skies 2018”