About 30 minutes after sunset on the evening of Saturday, July 18th, the Moon and radiant Venus will present a truly awesome sight in the western sky. The planet will appear to be touching the northern “horn” of the crescent Moon! This spectacle will rivet the attention of even the most casual of skywatchers looking upward. But there’s more to this celestial conjunction than just meets the eye.
The crescent Moon itself is always a lovely sight when gracing either the evening or morning twilight sky. But when it’s joined by one of the brighter planets, it’s a double treat — especially when that planet happens to also be in the crescent phase itself! And this can only occur with the inner planets Venus (and to a lesser extent) Mercury. It happens that Venus currently is at such a point in its orbit about the Sun. To see it as such you will need a small, low-power telescope. But here’s a surprise — the crescent Venus is also visible in binoculars! A magnification of 10-power or more is best. And the glasses also need to be held very steady, preferably being mounted on a tripod or other support of some kind. The ideal situation is for the fortunate possessor of image-stabilized binoculars, which have become not only more readily available today but also much more affordable than when they were first introduced to the market.
In addition to savoring the sight of these twin crescent worlds, apparently so close to each other in the sky (but actually quite far apart in space), there’s the thrill of watching them slowly move in relation to each other over a period of hours that evening until they finally set. This is the result of their respective orbital motions — mainly that of the Moon, which moves ever-eastward its own diameter every hour.
Readers may recall that Venus and the bright planet Jupiter had a spectacular “near miss” as described in last month’s installment of this column. While no longer so close as they were after dusk on June 30th (just a scant third of a degree apart), on the evening of the 4th of July look for them in the western sky about an hour after sunset at which time they will appear just 2 degrees apart. That’s close enough to easily fit into the field of view of any binocular — and also that of a low-power, wide-field telescope.
If you are one of those who believes that “nothing ever happens in the sky” — that everything is fixed in relation to each other and always looks the same — the events described above are guaranteed to change your mind!
— James Mullaney
Former assistant editor at Sky & Telescope magazine & author of nine books on stargazing. His latest, Celebrating the Universe!, is available from HayHouse.com.