Apr 2019

Moon passes through Beehive Cluster

Moon Occults Stars in Beehive Cluster May 10, 2019
by John Hlynialuk
On Friday night, May 10, from 10 pm local time or so until after midnight, several stars in the southern part of the Beehive Cluster will be occulted by the 6.3 day-old crescent Moon. Some of the stars are double, one is triple and one is quadruple, and though these will be difficult to observe in the vicinity of the bright Moon, they may be still “observable” -read on.


Stars of 6th and possibly 7th magnitude will be detectable, but don’t count on seeing 12th magnitude in the bright moonlight. In any case, there may be a possibility of “detecting” the doubles or multiples as step-wise changes in the light level. First one, then the other of the close pair is occulted by the optically very shape moon’s edge -a sequence that may take only a fraction of a second, but if you look for it, it may be detectable. Event no. 5 and 9 are good candidates for these. If you see a drop in the light from the star that looks like it faded first, then went out entirely, that may be each star blinking out in succession.

In general, occultations of stars by the Moon are neat to watch and occur fairly often. In 2019, the RASC Observer’s Handbook list 32 of these (for Toronto) and though there are no 1st magnitude stars involved, there is Tejat, μ-Geminorum, a 2.9 magnitude star occulted twice late in the year. Also, for this area will be a daytime occupation of Venus by the very thin crescent Moon only 4 degrees from the Sun on July 31.

Occultations of stars by the dark limb of the Moon are almost instantaneous and especially neat if there are several total occultations in series like we get May 10 or during totality of lunar eclipse. One gets a real sense of the Moon’s motion through the heavens from events like these.
Click on the diagram and/or table below to download a copy

M44 Moon pass May 10_edited-1

Diagram above from Sky Safari (with additional graphics added) illustrates the path of the 38% sunlit Moon passing through M44 from 10:10 pm EDT to just after midnight May 11. A pdf version of the star chart is available on the BAS website. Chart above does not show BS Cancri (BS Cnc) No.1 below, the first star to be occulted, and it will be faint, almost 9th magnitude.


Screen Shot 2019-04-13 at 6.51.02 PM

Table above gives times of events determined manually from Sky Safari 5 Pro for Owen Sound, ON. Times will not vary too much from these values if you are within 20 or 30 km of Owen Sound and are conservative (early) by about a minute. But if you are farther west times can be several, meaning many, minutes early and the opposite, later, to the east. Check your own software for your own geographic location. Differences of 15 minutes or more will occur across a province like Ontario.