Moon Covers Venus on September 14, Visible From Europe

Tomorrow morning, Monday, September 14, the Moon will block Venus, the second planet from the Sun, for a little over an hour. The event happens in the middle of the day, against a blue sky, and is visible from parts of Europe, Africa, western Asia and western Russia, while it cannot be seen at all from North or South America. According to NASA, this is the second of three Venus occultations by the Moon this year, following the one on June 17, which photographer Joel Kowsky captured from Washington.

On the evening before the occultation, September 13, a thin crescent Moon, about ten percent illuminated, already sits close to Venus, low in the western sky. Portal 021.rs recommends watching the pair shortly after sunset, from a spot clear of tall buildings and trees. According to Astronomy.com, Venus is then only eight degrees above the horizon twenty minutes after sunset, with the star Spica, 250 light years away, visible above and to the right of the Moon. Mercury sits nearby too, just two degrees off, but it sets within about ten minutes and is hard to catch by eye.

When exactly does the Moon cover Venus?

Unlike the evening pairing, the occultation itself on September 14 happens in the middle of the day, and the exact timing depends on where you are watching from. Across the whole zone of visibility the event runs, according to Telescope Advisor, from 09:26 to 13:42 UTC, or 11:26 to 15:42 Central European Summer Time. That is not the time for one point on Earth but a range covering every location together, since parallax means the Moon covers Venus at a slightly different moment depending on where an observer stands.

More specific figures exist for a handful of central European cities. Sterngucker reports that Venus disappears in Vienna at 11:34 and reemerges at 12:42, 68 minutes later; in Munich at 11:31 and 12:39; and in Berlin at 11:37 and 12:40. The Ukrainian outlet Universe Magazine gives the timing for Kyiv: the dark, unlit edge of the Moon touches Venus at 12:53:05 Kyiv time, or 11:53:05 Central European Summer Time, and the planet reemerges through the illuminated crescent at 13:47:08 Kyiv time, or 12:47:08 Central European Summer Time. None of the sources reviewed gives a time specific to Belgrade.

Venus disappears behind the Moon’s dark edge during the occultation and reemerges from behind the illuminated crescent, and that second moment, according to Universe Today, is the more striking of the two: the planet appears to suddenly pop out of an empty patch of sky. The Moon, per the same source, takes just over a minute to cross the entire illuminated portion of Venus’s disk.

Why the event is hard to see with the naked eye

At the moment of the occultation the Moon is a thin waxing crescent, twelve percent illuminated according to Sterngucker and Universe Today, or fourteen percent according to Telescope Advisor. Venus shines at a magnitude between -4.5 and -4.8, depending on the source, and through a telescope appears as a crescent 36 to 37 arcseconds across, 29 to 30 percent illuminated. That is, Telescope Advisor notes, roughly twice the apparent diameter of Saturn’s disk.

During the event the Sun sits 36 to 42 degrees high across central Europe, while the Moon and Venus stand about 42 degrees away from it, far enough for safe viewing as long as observers carefully avoid looking toward the Sun itself. The Moon is low when Venus disappears, just 8.5 degrees above the horizon in Vienna and only 1.6 degrees in Cologne, climbing to nine to sixteen degrees by the time Venus reemerges. That is why the pair has to be sought low in the southeast, and the advice from several sources is the same: binoculars or a telescope are close to essential, since the bare planet is hard to spot in the daytime blue sky without aid. Anyone attempting a photograph, Sterngucker advises, should use a telephoto lens of at least 300 millimeters, a 1/500 second exposure, ISO 100 and an aperture of f/8.

The occultation series continues after September 14

Serbian newspapers wrote about a related event a week earlier: on September 8 the Moon covered Jupiter in broad daylight, visible from the Americas. The Venus occultation on September 14 is the next in a series NASA counts as the second of three this year, while the final Venus occultation of the year falls on November 7 and is visible only from southern South America.

A week later Venus also reaches its greatest brightness of this year’s cycle, though sources disagree on both the date and the figure. EarthSky states the planet will be brightest on September 18 at 23:00 UTC, which means early morning on September 19 Central European Summer Time, at magnitude -4.8. Universe Magazine, on the other hand, puts the peak on September 22, at magnitude -4.6, and adds that Venus could theoretically be visible in daylight that day too, between 15:00 and 17:00 Kyiv time.

Where the sources disagree

The data on this event is not fully consistent in any single detail, apart from the basic fact that the occultation will happen. The Moon’s illumination ranges across the sources from twelve to fourteen percent, Venus’s brightness from magnitude -4.5 to -4.8, and the total duration of the occultation, from disappearance to reemergence, from forty to sixty eight minutes, depending on the observing location and the source cited. None of the sources reviewed gives an exact time for Belgrade, so local observers will have to rely on tables for central European cities or their own calculation in a planetarium app. The sources do not even agree on the date of Venus’s peak brightness a week later, and the gap between September 18 and September 22 remains unexplained in the material reviewed. What every source agrees on is that this is a rare event: the occultation of a bright planet by the Moon, seen from a single point on Earth, happens only once every few years, and this time it happens in broad daylight.