The UK enjoyed a weekend of vivid sunsets and sunrises, with the moon taking on a distinct orange hue. Monday night also promises the relatively rare lunar phenomenon of a blue supermoon, as a blue moon and supermoon coincide.
Why was the sky red and the moon orange?
The spectacular shades over the weekend in the UK are due to smoke from wildfires across the Atlantic in North America. According to the Met Office, a red sky appears when dust and small particles are trapped in the atmosphere by high pressure. It scatters blue light, leaving only red light to give the sky its notable appearance.
When the moon is low, it looks more orange because its light has to pass through a greater thickness of Earth’s atmosphere, according to the BBC’s Sky at night magazine. In summer the moon is below the celestial equator when it is full or almost full, so from the UK it does not rise high enough above the horizon to lose its orange hue.
What is a supermoon?
According to Nasa, a supermoon occurs when a full moon coincides with the moon’s closest approach to Earth in its elliptical orbit, a point known as perigee. This occurs approximately three to four times a year.
At its closest, the full moon can appear up to 14% larger and 30% brighter than the faintest moon of the year, which occurs when it is furthest from Earth in its orbit.
A supermoon can be difficult to detect visually, but it does have an effect on Earth. Because the moon is at its closest approach, it can cause higher than usual tides.
This supermoon will appear full in the sky for three days.
What is a blue moon?
Confusingly, there are two different definitions of a blue moon.
Normally there are 12 full moons in a year, one in each calendar month. But the lunar cycle does not always match our calendar.
A blue moon happens every two to three years when there are two full moons within a single calendar month. But a blue moon is also defined as the third full moon in an astronomical season, with the astronomical seasons beginning and ending at the equinoxes and solstices.
Monday night’s blue supermoon is under the seasonal definition. There was also a blue supermoon under the monthly definition last August.
The moon will not appear blue. In fact, it will appear more red or yellow at dusk thanks to the light refracting around the atmosphere at the horizon.
How rare is a blue supermoon?
According to Nasa, Monday night’s combination of a full moon, a super moon and a blue moon is quite “irregular”. The terms blue moon and supermoon are not scientific, meaning that definitions for the terms vary, adding to the variability of estimates for when the next blue supermoon might be.
Can you see the blue supermoon in the UK?
The full blue supermoon will become 100% full at 19:25 on Monday night. The moon will rise in the roughly eastern sky around 8:50 p.m. and will then set in the western sky around 6:35 a.m. Tuesday morning.
According to BBC weather presenter Simon King, the weather forecast does not look favourable, with clouds and patchy rain spreading eastwards across the UK. There will be some limited times when the sky should clear at different stages of the night.
Although the blue supermoon won’t technically be full Tuesday night, it will still be nearly full and there will be a better chance of clear skies, King says.
