Magnitude +3.2 star Eta (η) Geminorum is occulted (hidden) by the 18-day-old waning gibbous Moon on the evening of Friday, 15 November 2019 as seen from parts of the British Isles. This looping animation shows the event’s progress as seen from London and Liverpool, clearly demonstrating the effect of geographical latitude; observers in the capital will see it, whereas those in the north and west of the UK will not. Precise circumstances and timings are given in the article below. AN graphic by Ade Ashford.If you happen to live in the far south of Wales and a large swathe of southern and eastern England, clear skies around 10pm GMT on Friday, 15 November will permit you to view naked-eye star Eta (η) Geminorum, otherwise known as Propus (α = 06h14.9m δ = +22°30′ J2000), slip behind the northern polar regions of the rising 18-day-old waning gibbous Moon. The occultation will take place some 30 degrees above the eastern horizon.
Furthermore, those lucky observers who happen to live on a line drawn between Porthcawl of the Welsh coast through just south of Birmingham and on to the Lincolnshire Wolds, this is going to be a grazing lunar occultation. If one is situated exactly on the graze line (see the diagram below), the star will appear flicker in and out of sight as it is alternately hidden by mountains on the northern limb of the Moon then exposed again as it shines through a lunar valley, affording an awesome demonstration of the Moon’s orbital motion.The grazing lunar occultation line for the naked-eye star Eta (η) Geminorum on the evening of 15 November 2019. Anywhere south and east of the blue line will see the star hidden by the Moon, while those to the north and west will witness a near miss. Base map by Guide 9.1, AN graphic by Ade Ashford.Predictions of the disappearance and reappearance times for Eta (η) Geminorum, aka Propus, on 15 November 2019 as seen from selected UK locations. All times GMT/UT.German astronomer and geophysicist Julius Schmidt determined that Eta Geminorum was a variable star in 1865. Classed as a semiregular variable and an eclipsing variable between magnitude +3.15 and 3.9 with a period of about 231 days, Propus is also triple star.
The innermost pair of η Geminorum form a spectroscopic binary too close to be resolved visually, but the outermost companion is a magnitude +6 star just 1.6 arcseconds away at position angle 252°. If the seeing is good enough, can you resolve the pair in 10-cm (4-inch) aperture telescopes and larger at magnifications of around 200×? If so, the fainter companion star is occulted (and reappears) just prior to the brighter primary star.