2020 October 10

Stars 44 Oph and λ Sqr in early evening lunar occultations, Oct. 20-21

Ade Ashford

Magnitude +4.16 star 44 Ophiuchi, otherwise known as b Ophiuchi, lies 13 degrees east of Antares in Scorpius. The former is occulted at the dark limb of the 4½-day-old waxing crescent Moon between 18:06 and 18:18UT (7:06pm and 7:18pm BST) as seen from the British Isles on Tuesday, October 20. The occultation occurs when the Moon is about 6 degrees above the southwest horizon, so the reappearance of 44 Ophiuchi at the Moon’s bright limb is unobservable from the U.K.

Fast forward 24 hours and the by now 5½-day-old Moon lies very close to magnitude +2.82 star Lambda (λ) Sagittarii, otherwise known as Kaus Borealis, the tip of the ‘Teapot’ asterism’s ‘lid’ in Sagittarius. Depending on where you live in the British Isles, the star disappears at the dark lunar limb between 18:10 and 18:23UT (7:10pm and 7:23pm BST) on October 21.

Note that the Moon lies just 8 degrees high in the south-southwest at the disappearance of λ Sgr. If you have exceptionally clear skies, you might see the star’s reappearance at the bright limb approximately one hour later, but the setting Moon will be very low in the southwest.