In the pre-dawn sky on Sept. 18, 2017, the old crescent moon joined a chain of naked-eye objects low in the eastern sky. The moon will block all four of these objects — Venus, the star Regulus, Mars and Mercury — over the course of the day, in occultations that won’t be seen by many skywatchers.
Credit: SkySafari App
The moon is throwing a historic block party today (Sept. 18).
Earth’s nearest neighbor occulted, or covered up, Venus and the bright star Regulus in the sky this morning, and will swallow up Mars and Mercury this evening.
The moon hadn’t occulted three planets in a single 24-hour span since March 2008, and it won’t do so again until July 2036, according to EarthSky.org.
But don’t get too excited, skywatchers.
“Overall, this string of planetary occultations may be more of an academic than observational interest, because much of the world is not particularly well-situated for watching even one of these four occultations,” EarthSky.org wrote yesterday (Sept. 17).
Indeed, all four events pretty much pass by North America and Europe, generally favoring the Southeast Asia and Pacific regions.
“Even at that, the occultations of Regulus, Mars and Mercury will be extremely hard to observe because they occur in a daytime sky,” McClure wrote. “Undoubtedly, you’ll need a telescope to see any one of these lunar occultations — that is, if any one of them even takes place in your sky.”
The moon will block Mars at about 4 p.m. EDT (2000 GMT) today in an occultation visible from parts of South America, Central America, Mexico and the Pacific Ocean. The Mercury occultation takes place at around 7 p.m. EDT (2300 GMT); it will be visible from the mid-Pacific into Southeast Asia and parts of China.
You can see visibility maps for each of these events here: http://earthsky.org/tonight/occultations-galore-on-september-18
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