When is the next supermoon? What does perigee mean? What is a moonquake? All you wanted to know about supermoons.
What is a supermoon?
The distance between the Moon and the Earth varies because the Earth is not right at the centre of the Moon’s orbit, and the Moon’s orbit is not a circle, it’s an ellipse. So there will be a lunar perigee when the Moon is closest to the Earth, and a lunar apogee when it’s thousands of miles farther away.
If the lunar perigee occurs very close to a full moon, then we see a supermoon. If a lunar apogee occurs very close to a full moon then we see a micromoon.
The term supermoon originates from a concept in astrology, but has been adapted and given a strict definition within astronomy. If the Moon is within 10% of its closest distance at the moment of full moon, it is considered to be a supermoon.
During a supermoon, the Moon appears up to 14% bigger and 30% brighter than the furthest a full moon can be.
When is the next supermoon?
The next supermoon is on Sunday, 3 December 2017
2017: 3 December
2018: 2 January
2019: 21 January, 19 February
How can I see the supermoon?
So long as there’s not too much cloud, the full Moon will be an unmistakable white orb in the sky. Seeing moonrise just after sunset or moonset just before sunrise will be an impressive sight as it will appear enormous compared to the surrounding landscape, due to an illusion.
During moonrise, the Moon looks bigger than it is because our brain doesn’t understand that the sky is a dome. It falsely projects things near the horizon to appear larger than they actually are.
What is a supermoon lunar eclipse?
An eclipse of the Moon occurs when the Earth lies directly between the Sun and the Moon and the Moon lies in the shadow of the Earth. During a total eclipse, the Moon does not disappear entirely but turns a deep, dark red. The Moon is illuminated by light that has passed through the Earth's atmosphere and has been bent back towards the Moon by refraction.
The last time a total lunar eclipse coincided with a supermoon was in 27 and 28 September, 2015.
When was the last supermoon?
Giorgia Hofer explains her photo ‘Super Moon’, taken on 14 November 2016, which was shortlisted in the Our Moon category in the Insight Astronomy Photographer of the Year competition 2017.
On the night of 14 November 2016, the Moon was at perigee at 356,511 km away from the centre of Earth, the closest occurrence since 1948. It will not be closer again until 2034. The Moon on this night was 30% brighter and 14% bigger than other full moons. In this shot, the Moon is setting behind the Marmarole, a mountain group that is in Cadore, in the heart of the Dolomites in Italy.
How do supermoons affect tides?
The tides are caused by the gravitational forces of the Sun and the Moon on the Earth’s oceans. When the Moon is closer to the Earth during a supermoon, the gravitational pull is slightly stronger, and so the tides are bigger. However this effect is almost negligible, with only a couple of inches difference between a normal full moon and supermoon tide.
However, full moon and new moon tides can be much bigger than tides at other times in the lunar month, as the Sun adds its own gravitational pull into the mix, producing the so-called spring tides.
Interesting facts about the Moon
Shortlisted entrants from the Insight Astronomy Photographer of the Year Award share their top facts about the Moon.
- The Moon is Earth's only permanent natural satellite. It is the fifth-largest natural satellite in the Solar System, and the largest among planetary satellites relative to the size of the planet that it orbits.
- Following Jupiter's satellite Io, the Moon is second-densest satellite among those whose densities are known.
- The Moon is in synchronous rotation with Earth, always showing the same face, with its near side marked by large dark plains (volcanic ‘maria’) that fill the spaces between the bright ancient crustal highlands and the prominent impact craters. As seen from the Earth, it is the second-brightest regularly visible celestial object in Earth's sky, after the Sun.
- The Moon’s surface is actually dark, although compared to the night sky it appears very bright, with a reflectance just slightly higher than that of worn asphalt. Its gravitational influence produces the ocean tides, body tides, and the slight lengthening of the day.
- From Earth, both the Sun and the Moon look about same size, this is because, the Moon is 400 times smaller than the Sun, but also 400 times closer to Earth.
- The Moon is drifting away from the Earth. The Moon is moving approximately 3.8 cm away from our planet every year.
- The most widely-accepted explanation is that the Moon was created when a rock the size of Mars slammed into Earth, shortly after the solar system began forming about 4.5 billion years ago.
- Everyone knows that the Moon is partly responsible for causing the tides of our oceans and seas on Earth, with the Sun also having an effect. However, as the Moon orbits the Earth it also causes a tide of rock to rise and fall in the same way as it does with the water. The effect is not as dramatic as with the oceans but nevertheless, it is a measurable effect, with the solid surface of the Earth moving by several centimetres with each tide.
- The Moon has quakes, called not earthquakes but moonquakes. They are caused by the gravitational influence of the Earth. Unlike quakes on Earth that last only a few minutes at most, moonquakes can last up to half an hour. They are much weaker than earthquakes though.
- There is water on the Moon! This is in the form of ice trapped within dust and minerals on and under the surface. It has been detected on areas of the lunar surface that are in permanent shadow and are therefore very cold, enabling the ice to survive. The water on the Moon was likely delivered to the surface by comets.