Daytime occultation of REGULUS
WHEN: 5 January from 07:30 UT
An interesting event occurs on the morning of 5 January, providing you a fantastic opportunity to see a night-time star during the day. At 07:30 UT, locate the 85%-lit waning gibbous Moon. Mag. +1.4 Regulus (Alpha (_) Leonis) will be 0.5º to the east of the Moon’s eastern limb. With sunrise less than an hour away, the sky will be getting bright at this time. Keep watch using binoculars or a telescope at low magnification, as the Moon creeps ever closer toward the star.
Regulus is occulted by the Moon’s bright limb just after 08:20 UT for observers in the centre of the UK. This time varies slightly with location, so we recommend that you start watching from around 08:10 UT. Reappearance is just before 09:16 UT in broad daylight. Despite this, the intense pin-point brilliance of Regulus should shine though if the sky is transparent. Start watching for the reappearance from 09:05 UT to ensure you don’t miss it.
The full Moon on 2 January is the perigee full Moon of 2018. Perigee is the point in an elliptical orbit around the Earth when the distance between a body and our planet is at a minimum. The nature of the lunar orbit and phase cycle means that throughout the year, successive full Moons occur at positions that slowly move around the orbit. One of these will occur closer to the perigee point than the others. In 2018 this is the full Moon of 2 January. Being closer than the others, this full Moon will also appear slightly brighter and larger. Another consequence of lunar perigee is that the Moon’s apparent speed across the sky is up to 6% faster than when it’s at its farthest position from Earth, lunar apogee. The full Moons either side of the perigee full Moon are only marginally smaller and dimmer. On 2 January, the Moon is full at 02:25 UT, and well positioned for optimum brightness and apparent size for the UK. The term ‘perigee full Moon’ is often described in popular culture by the term ‘supermoon’. This originally astrological term describes any full or new Moon which occurs within 90% of the perigee or apogee position. A second full Moon occurs on 31 January, and technically it’s another supermoon. The second full Moon in a month has become known as a ‘Blue Moon’, though originally this term referred to the third full Moon in an astronomical season with four of them. March offers a repeat performance with a full Moon on the 2nd and another on the 31st.