Two crescents — the Moon and Venus — meet in the sky in the wee hours of June 19th.
Should weather conditions be favorable, be sure to set your alarm clock for around 4 a.m. local time on Friday, June 19th, then proceed to a location where you have a clear and unobstructed view of the east-northeast horizon. A beautiful celestial tableau will be your reward, as an exceedingly thin crescent Moon rises in close proximity to the brightest planet in our sky.
Early risers who are up at this hour, and who are unaware or have no advance notice, will certainly wonder as they cast a casual glance toward the skinny Moon that morning: What is that “large silvery star”? Sometimes, such an occasion causes a sudden spike of phone calls to local planetariums, radio and TV stations and even police precincts. Not a few of these calls excitedly inquire about “the UFO” that is hovering in close vicinity of our natural satellite.
The object keeping close company with the Moon on this particular June morning will be dazzling Venus (magnitude -4.5), the unrivaled morning star whose dawn appearance will soar to magnificent prominence during the summer months.
Most observers in the U.S. will see Venus and the Moon pair up: As seen from the western U.S., Venus and the Moon will appear only roughly 2° apart; from the central U.S. they’ll appear even closer together, only about 1° apart. And along the East Coast the gap between them will amount to less than a degree.
THE MOON HIDES VENUS
But those living in northern and eastern New York, New England, and the Canadian Maritimes, await an even more spectacular sight. As the Moon comes up above the horizon, it will be hiding Venus behind it. Some minutes later, Venus will emerge dramatically from behind the Moon’s dark limb – the end of its occultation.
Readers can readily see this event without optical aid. However, binoculars or a telescope will give a much better view, as both objects will be thin crescents, the Moon being 4% sunlit and Venus 8%, adding to the beauty of the event. The emergence for most will take place near a position angle of 40° as measured clockwise from the top of the lunar disk, or just past 1 o’clock.
Unlike a star — a point source of light, which appears to suddenly “pop-on” when it reappears from occultation — Venus’ disk measures 51 arcseconds across and will take about 90 seconds to completely emerge into view. The actual observed duration will be considerably less, though — more like 10 seconds, because only part of the planet is sunlit.
WHAT LOCATIONS WILL SEE THE OCCULTATION?
On the accompanying map, places to the right of a line running from Watertown to Riverhead, New York, will be able to see Venus emerge from behind the Moon; to the left of that line Venus emerges before moonrise. Local emergence times, altitude and azimuth information is provided for 11 U.S. and Canadian cities. For other cities such data can be determined using interpolation.
Local circumstances for the reappearance of Venus on June 19, 2020
|Providence, RI||3:58 a.m.||4:06.5 a.m.||1°||65°||5:11 a.m.|
|Boston, MA||3:55 a.m.||4:06.9 a.m.||1°||66°||5:07 a.m.|
|Concord, NH||3:55 a.m.||4:08.0 a.m.||1°||66°||5:06 a.m.|
|August, ME||3:44 a.m.||4:08.7 a.m.||3°||67°||4:55 a.m.|
|Montpelier, VT||3:56 a.m.||4:09.5 a.m.||1°||65°||5:06 a.m.|
|Montreal, PQ||3:56 a.m.||4:11.1 a.m.||2°||65°||5:05 a.m.|
|Halifax, NS||4:18 a.m.||5:07.7 a.m.||7°||71°||5:29 a.m.|
|Fredericton, NB||4:26 a.m.||5:09.8 a.m.||3°||67°||5:36 a.m.|
Local circumstances for the entire occultation (disappearance and reappearance) of Venus
|Sydney, NS||3:59 a.m.||4:20.1 a.m.||2°||65°||5:09.1 a.m.||10°||74°||5:09 a.m.|
|Charlottetown, PE||4:11 a.m.||4:21.8 a.m.||1°||63°||5:09.1 a.m.||8°||72°||5:20 a.m.|
|St. John’s, NF||4:07 a.m.||4:49.1 a.m.||7°||70°||5:40.9 a.m.||16°||80°||5:03 a.m.|
The farther north and east one goes, the higher the Moon will be, but also the brighter the twilight sky will get. The best view will be just to the right of the “Disappearance of Venus at Moonrise” line in Prince Edward Island and eastern Nova Scotia, where the entire occultation will be visible before sunrise. “Nocturnal” (pre-sunrise or post-sunset) occultations of Venus are quite rare.
In the February 2011 Journal of the British Astronomical Association, Jean Meeus and I determined how often this happens for a specific location. Every 31 years, on average, we may witness Venus both disappear and reappear, while every 21 years, on average, we may witness either one or the other. The next such opportunity for New England and the Maritimes comes earlier than that, though, on September 13, 2031.