A rare blue moon is set to pass overhead — and be visible tonight to most people in the UK and elsewhere.
The moon will be most visible towards the south of the UK, which is forecast to have clear skies. There will be less cloud cover towards the early evening.
Since the satellite itself doesn't actually change, the blue moon will be visible from anywhere that could normally see the non-blue one.
(The International Space Station should also be visible a few times through the night, if you want to kill two sights with one look.)
There won’t be much to see beyond the normal moon — it’s very unlikely that it’ll actually be blue, and that’s not where it gets its name from. The event is actually a quirk of the calendar that happens just over every two and a half years — the moon runs on a 29.5 day cycle, and therefore every so often there’s an extra day — so the moon itself doesn’t change or look any different from Earth.
But it will be extra big and bright, since it’s also approaching very close to the Earth. That will be what accounts for any more spectacular look this evening, rather than it being anything to do with being a “blue moon”.
(The moon itself does have some blue bits, as the Royal Observatory has pointed out, but they aren’t usually visible from Earth.)
Sometimes the moon does look blue from Earth. But that doesn’t have anything to do with the event happening tonight, and is instead caused by volcanic eruptions that spread ash into the sky and catch the light.
Astronomy Photographer of the Year 2015 - shortlisted images
Astronomy Photographer of the Year 2015 - shortlisted images
1/17 Moon and Antelao by Marcella Giulia (Italy)
Late afternoon at San Vito di Cadore, Italy the moon shines over Monte Antelao. The snow-covered dolomite ridge of the mountain and the Earth's only natural satellite bear a striking resemblance to one another, contrasting against the bright blue of the afternoon sky. The photographer noted the likeness of the image to a snowball bouncing down an inclined plane
2/17 The Mirrored Night Sky by Xiaohua Zhao (China)
An enthralled stargazer is immersed in the stars as the luminous purple sky is mirrored in the thin sheet of water across the world’s largest salt flat, Salar de Uyuni in Bolivia
3/17 The Night the Sky Exploded by Kris Williams (UK)
A rare sighting of a red aurora, caused by the emission of high-altitude oxygen, captured on film, dancing over the small fishing town of Eyrarbakki, on the south coast of Iceland. The result of a large geomagnetic storm caused by a large coronal mass ejection, this display that lasted for hours, was one of the most colourful that the photographer had ever seen, and was even visible before darkness had completely fallen
4/17 Star Trails over Green Lake by Dan Barr (USA)
Star trails illuminate the night sky over a campfire-lit Green Lake in the Hoover Wilderness of California. Star trails are a popular subject for astrophotographers to capture using long-exposure times. Whilst they appear to illustrate the movement of the stars, they are in fact depicting the rotation of the Earth on its axis
5/17 Calm Before the Storm by Julie Fletcher (Australia)
A phenomenal natural light show of a lightning storm emanating from the underside of ominous storm clouds juxtaposed with the gleaming stars of the Milky Way above them. The photographer had watched the storm front over Kati-Thanda-Lake Eyre National Park in South Australia for around two hours before capturing this tumultuous scene, using a graduated filter upside down to balance to exposure from top to bottom to showcase the beauty of our Galaxy
6/17 Great Nebula in Carina Bi-Colour by Terry Robison (Canada)
The hypergiant star Eta Carina glows against the background of swirling clouds of dust and gases that form the Carina Nebula. The Carina Nebula is one of the largest diffuse nebulae - meaning that it has no well-defined boundaries - in our skies and is about four times as large as the famed Orion Nebula
7/17 Thor’s Helmet (NGC 2359) by Adam Block (USA)
The distinctive shape of the nebula NGC 2359 has led to it also being known as Thor’s Helmet, resembling the headgear of the Norse God (and Marvel superhero). Around 11 thousand light years away, the overall bubble shape is mainly due to interstellar material swept up by the winds of the nebula’s central star Wolf-Rayet, an extremely hot giant thought to be in a pre-supernova stage
8/17 IC443 by Patrick Gilliland (UK)
Lying in the constellation of Gemini, IC443 is a galactic supernova remnant, a star that could have exploded as many as 30,000 years ago. Its globular appearance has earned the celestial structure the moniker of the Jellyfish Nebula
9/17 Roseta-NBv5 by Juan Ignacio Jimenez (Spain)
Measuring 50 light years in diameter, the large, round Rosette Nebula is found on the edge of a molecular cloud in the constellation of Monoceros the Unicorn. At the core of the nebula the very hot young stars have heated the surrounding gaseous shell to a temperature in the order of 6 million kelvins resulting in the emission of copious amounts of X-Rays. Here the photographer has applied a false colour palette to several pictures using narrowband filters, which only allow a specific colour of light to reach the camera, with each one linked to an interstellar gas, resulting in the striking blues and oranges
10/17 Solar Prominence by Gary Palmer (UK)
Searing hot loops of plasma radiate from the edge of our local star – the Sun – in a phenomenon known as a solar prominence. Emanating from the Sun’s photosphere; its outer shell from which light is emitted, prominences extend to the corona, which is the aura of the plasma surrounding it. A typical prominence covers over thousands of kilometres, with the largest ever recorded estimated to be over 800,000 kilometres, equalling roughly the radius of the Sun itself
11/17 Motind by Rune Engebo (Norway)
Living in Norway, the photographer had seen his fair share of aurorae, but on 21 January 2015 he witnessed the strongest variety of colours he had ever set eyes on in this beautiful explosion of purples and greens. Careening over the peaks of Senja, oxygen produces the greens and nitrogen the purples, seen in this particular display of the Northern Lights
12/17 C/2014 Q2 Lovejoy by Michael Jaeger (Austria)
Comet Lovejoy sails through the solar system in a green haze leaving cometary dust in its wake. C/2014 Q2 is the fifth comet to have been discovered by Australian amateur astronomer and astrophotographer, Terry Lovejoy. Towards the end of 2014 and into the beginning of 2015 the comet could be seen through binoculars or in some special cases with the naked eye soaring through Earth’s skies. The radiant blue-green contrasting against the backdrop of the night sky is due to the diatomic gas burning off it as it travels through space, and the disjointed tail illustrates the effects of a disturbance caused by solar winds
13/17 M42 Subtle V1 cropped by Patrick Gilliland (UK)
One of the most well-known astronomical objects in our universe is the Orion Nebula and this image depicts the wider region of the Orion Molecular Cloud Complex that is home to it. This complex is also home to another popular target for astrophotographers, the Horsehead Nebula, as well as Barnard's Loop and the Running Man Nebula that can be seen to the left of this photograph. The pinks and oranges that can be seen in the whorls of the nebulae are caused by the extremely hot hydrogen gas present in the structures
14/17 Full Moon over the Alps by Stefano de Rosa (Italy)
The majestic sight of the full moon setting behind the rose-tinted Alps. Taken in the silent surroundings of Superga hill in Turin, Italy, mere minutes before sunrise
15/17 Ascent of Angels by Brad Goldpaint (USA)
Following his first up-close encounter with a black bear, the photographer was relieved to reach his destination safely and capture this phenomenal image. A meteor can be seen piercing through the darkness as the Milky Way towers above the 4,392m peak of Mount Rainier in Washington, USA. The white lights dotted across the rocky paths of the mountain’s face are the headlamps of hikers ascending to the peak
16/17 Herschel 36: The Heart of the Lagoon by László Francsics (Hungary)
Situated some 5,000 light years away, the stellar nursery of the Lagoon Nebula lies in the constellation of Sagittarius. Despite being light years away the Lagoon Nebula is in fact one of the few star-forming nebulae that it is possible to see with the naked eye in optimum conditions from mid-northern latitudes
17/17 Aurora Panorama 3 by Jan R. Olsen (Norway)
The vivid green Northern Lights dance above Lyngenfjord, the longest fjord in Troms county Norway, tracing out the shape of the Earth’s magnetic field above the waters. The most common colour associated with aurorae, the green is produced by oxygen atoms and molecules energised by the impact of solar particles that have escaped the Sun’s atmosphere, causing them to glow brightly