If your eastern sky is clear at dusk on 19 February be sure to take a good look at the full Moon rising in the constellation of Leo. If it seems a bit bigger than usual then it’s due to more than just the lunar illusion, for this full Moon is the largest that you’ll see all year.
The Moon’s orbit is far from circular and its distance from Earth at closest approach, termed perigee, varies each lunar month. Tuesday, 19 February at 9:09 UT (9:09am GMT) sees the closest perigee of 2019 when the distance between centres of Earth and Moon is 356,763 kilometres. And the Moon won’t get any nearer Earth until 21 January 2023. Yet even this record will be surpassed by the 356,447-kilometre perigee of 6 December 2052 – the closest of the century.
The circumstances of 2019’s closest Moon get a little more interesting a few hours later on 19 February since full Moon occurs at 15:54 UT (3:54pm GMT). The proximity of perigee and a full Moon – giving rise to a lunar orb almost 8 percent larger than average on this occasion – is commonly called a supermoon, which is far more succinct than the term ‘perigee-syzygy of the Earth–Moon–Sun system’ preferred by astronomers.
Watch the supermoon live courtesy of the Virtual Telescope Project
Not only is next Tuesday’s full Moon the largest of 2019, but it’s also the third-largest full Moon of the next 10 years. In fact, you’ll have to wait until Christmas Eve 2026 to see a larger full Moon (calculated for the geocentre).