A supermoon occurs when a full moon coincides with the moon's closest approach to Earth in its orbit and it appears brighter and larger - here's everything you need to know about the rare phenomenon
Stargazers in the UK will tonight be treated to a dazzling blue supermoon in a rare event that's set to light up skies across the UK.
If you notice that the moon looks special, it's because you are witnessing a rare phenomenon in which the planet looks bigger and brighter than usual. Supermoons normally happen around three to four times a year and is the phenomenon which occurs when a full moon is at its closest point in orbit to Earth, therefore appearing even bigger in size. This is known as a perigee.
The phenomenon is also known as a Sturgeon Moon, named after sturgeon fish that are found in the Great Lakes of North America at this time of year. Despite the name, the Blue Moon isn't actually blue. You may have heard the term "once in a blue moon", which has come to mean a notably rare event.
What time will we be able to see the moon?
Tonight's full blue supermoon will become mostly visible at 7:25pm BST - but many us of may not actually be able to witness it. Moon rises at around 8:50pm BST in the roughly east sky and will then set on Tuesday morning at around 06:35 in the western sky. However the weather forecast is not looking all that favourable with cloud and patchy rain spreading across the UK. There will be some limited times where the skies should clear at different points throughout the night.
Where is best to see the blue supermoon?
The weather could of course be the biggest stumbling block in terms of seeing the blue supermoon. If there isn’t too much cloud cover, it’s best to get head out from cities and town centres to rural areas with less light pollution to get the best views of the moon.
You don’t need to do much other than look up and enjoy the scenery. But if you do own a telescope, or even a pair of binoculars, you’re likely to see even more detail on the lunar surface than usual. A weather map from the BBC, dividing the country into three sections, shows in the south and east of England there will be cloud breaks in the evening which will offer a less obscured view before it becomes more cloudy later in the evening. Meanwhile, the west, Wales, the Midlands and the north of England will start more cloudy but become clearer later in the evening. Those in Scotland and the Highlands will be blessed with clearer skies later on in the night.
What exactly is the Sturgeon Blue supermoon?
A supermoon occurs when a full moon coincides with the moon's closest approach to Earth in its orbit and it appears brighter and larger in the sky than a normal moon. The August full moon is known as the Sturgeon Moon. It gets its name because North American fishing tribes would see the appearance of lots of sturgeon fish around this time of year.
What is a Blue Moon?
There are actually two types of Blue Moon - seasonal and monthly - but both definitions have nothing to do with the moon's colour. A seasonal Blue Moon is the traditional definition of a Blue Moon and refers to the third full moon in a season that has four full moons according to NASA.
The second definition — which arose from a misunderstanding of the original — is the monthly Blue Moon, referring to the second full moon in a single calendar month. Today, this monthly Blue Moon is accepted as an alternative definition rather than a mistake, according to Time and Date.
A moon cycle phase typically lasts one month, and on earth we usually experience 12 full moons each year. The moon phases actually take 29.5 days to complete which means it takes just 354 days to complete 12 lunar cycles. So every 2.5 years or so a 13th extra full moon is observed within a calendar year. This 13th full moon doesn't conform to the normal naming scheme and is referred to as the Blue Moon.
What is a supermoon?
When the moon is at its closest point to Earth, it's known as the lunar perigee. This occurs at about 253,000 miles, or 405,500km from the planet. The reason this occurs is that the moon's orbit isn't a perfect circle, so it varies how close the orb is from Each.
NASA's Noah Petro, deputy scientist of the Lunar Reconnaissance Orbiter mission, told Space.com: "The main reason why the orbit of the moon is not a perfect circle is that there are a lot of tidal, or gravitational, forces that are pulling on the moon." He added: "You have all of these different gravitational forces pulling and pushing on the moon, which gives us opportunities to have these close passes."
What is a super Blue Moon?
The August 19 super Blue Moon is particular special as it's a combination of a full moon, a supermoon and a Blue Moon all occurring at the same time. According to NASA, this combination only occurs once every 10 years on average. However it can even be as long as 20 years between super Blue Moons.
When is the next super Blue Moon?
Tonight's blue moon is a rather rare event. But if you miss it, fear not - another supermoon is on the horizon next month on Wednesday, September 18. And there will be another on October 17. During this late supermoon event, the moon will be near its closest approach to the Earth and may look slightly larger and brighter than usual.
