To give you an idea how far away the Moon is
In average — and in theory, we can fit 30 more than Earths between Earth and the Moon. When the Moon is closest to Earth however, we can only fit 28 to 29 Earths, when is furthest apart we can fit 32 about Earths. That is two Earth’s diameters difference in average and four diameters between the closest and the furthest. That’s a lot of real estate! ! The diameter of the Earth is 12,742 km if you are curious. And if you are still curious, Moon’s diameter is 3475 km.
More so, if we took all the planets in the Solar System (also in theory), and line them up, they would just fit between Earth and the Moon.
From Earth to the Moon is more or less the distance that light travels in one second. It’s actually an average of 1.2 seconds to the Moon if you are travelling at the speed of light.
A Supermoon is a Full Moon that is at perigee (closest to Earth)
Most models of the Moon orbiting the Earth depict its orbit as being circular but we know from Kepler’s Laws that celestial bodies orbit one another in an ellipse rather than a circle. What this means is that sometimes the Moon is closer to the Earth than at other times in its orbit. When this is combined with the Moon being a Full Moon and the media hype around the subject, the Moon becomes a Supermoon. The common astronomical definition is however perigee syzygy (of the Earth-Moon-Sun system) or Perigee Full Moon. The last of the perigee Full Moon for this year is today, the 8th of April 2020 but we really like to say syzygy so we will refer to it as the perigee syzygy Moon.
Astrologer (which is different from astronomer) Richard Nolle coined the term Supermoon in 1979 and media picked up on it, but you need to know that Supermoon is not an official astronomy term. Nolle defined the Supermoon as ‘a New or a Full Moon that occurs when the Moon is at or near (within 90% of) its closest approach to Earth in its orbit’. Nobody knows why he chose the 90% cut off in his definition.
When does it happen?
Most media articles circulating on the internet are written for the Northern Hemisphere, which means you might read that the Full Moon happened on Tuesday. In New Zealand, the Full Moon occurred today, Wednesday the 8th of April.
Though the Full Moon occurred today at 2:35pm — from Wellington, it does not matter because we would not have been able to see it as it was below the horizon. The actual time when the Moon is at its closest to Wellington is at 12:44am tomorrow morning at a distance of 352,346 km away. Full Moon occurred today at 2:35pm and the distance from Wellington, was about 360,945 km according to Sky Safari.
The actual time that the Moon is the closest to the Earth in it’s orbit, the place we call the perihelion on the elliptical orbit occurred at 6:05 this morning when the Moon was 356,906km away, that’s the distance from the centre of the Moon to the centre of the Earth.
Nevertheless, even though at 2:35pm NZST on the 8th of April 2020 the Moon was officially full and Full Moon is just a moment in time (when the Moon is fully illuminated by the Sun) in lay terms, we still consider the Moon tonight a Full Moon as it will be in the sky all night long. Full Moon always rises at sunset and sets at dawn.
Last year’s Supermoon in March was 360,242 km away, about the distance it takes light to travel in 1.2 seconds. Just like last year, this is the third Supermoon in a row.
Now an important thing to remember is that we did not actually see the full Moon at its closest approach because the two occurrences don’t actually line up that well. The Moon was closest to Earth after it set in Wellington this morning which happened at 6:05am, so technically we missed the perigee Moon. The Full Moon, happened at 2:35pm today so technically we missed the Full Moon as well.
But at 12:44am in the morning we will see the Moon at its closest approach where it will be 352,346 km (1.18 light seconds) and 33.9 arc minutes in apparent diameter. The Moon will be 99.5% illuminated so it will certainly appear to be full but in reality it’s just past being at maximum illumination. So there’s no need to be picky but technically it’s not a Supermoon, then again the term Supermoon has no real scientific basis anyway other than to describe the time when the Moon is full and close to perigee. Out of interest the technical name is perigee syzygy. The term syzygy refers to the straight line of three bodies, in this case the Moon, the Earth and the Sun all lined up.
Again, many media outlets recommend that the best time is to observe the Moon when is full, what they mean to say is that Full Moon is best observable at Moonrise and Moonset. When observing the Moon through a telescope the best time is when the Moon is NOT fully illuminated. This is because the Sun then casts shadows over the Moon’s craters and they stand out. In the picture above the Moon was about 90% illuminated and clearly shows some of the spectacular views you can get of the Moon near the terminator. The terminator is the name of the line that separates shadow from light on the face of the Moon.
On the horizon, as it rises, the Moon will probably look fabulous and extremely big. That’s actually an illusion and how far away the Moon is from us doesn’t really make any difference to the eye. You can take that Moon Spell away if you stretch your arm and cover the Moon with your pinky. The width of your pinky will be the same size as the Moon. A big Moon near the horizon is always an illusion, is a trick that our brain plays on us actually and if you click on the link, you will read what NASA has to say about it.
Happy Full Moon Night everyone!