It was an evening to remember for skywatchers or stargazers in most parts of the world, for they were witness to a rare celestial event, aptly described by many as “once in a generation".

The event, called the ‘Super Blood Moon’ (or #SuperBloodMoon, if you are a Twitter person), saw the Supermoon phenomenon combine with a lunar eclipse (where the Sun, the Earth and a brighter, much larger Moon lined up together). The result? The Moon appeared blood red in colour, nearly 30% brighter.

For the astronomically inclined, the National Aeronautics and Space Administration (Nasa) has all the details—the conjunction, the coordinates and the duration—from Sunday’s eclipse, right here.

So what exactly is a Supermoon?

As described by the BBC, a Supermoon is a phenomenon that occurs when, “a full or new Moon coincides with a Moon that is nearing its minimum distance (perigee) to Earth. The Moon takes an elliptical orbit around Earth, which means that the average distance between the two changes from as much as 405,000km (its apogee) to as low as 363,000km at the perigee". Simply put, the Supermoon occurs when the Moon is at its closest to the Earth. Nasa says the phenomenon can make the Moon appear larger by nearly 14 times its usual visible size.

As for the breathtaking blood red colour, here’s Nasa’s explanation for the same: “During a total lunar eclipse, white sunlight hitting the atmosphere on the sides of the Earth gets absorbed and then radiated out (scattered). That is, the atmosphere filters out (scatters away) most of the blue-colored light... what’s left is the orange- and red-coloured light. This red coloured light passes through our atmosphere without getting absorbed and scattered, before the atmosphere bends it (refracts it) back out, projecting indirect, reddish light on to the Moon. The reddish light projected on the Moon is dimmer than the full white sunlight that the Moon typically reflects back to us. That’s because the light is indirect and because the red-coloured wave lengths are only part of what makes up the white light from the Sun that the Moon usually receives."

Besides, Nasa notes, “The reason why the Moon turns red during a total lunar eclipse is related to why we have such beautiful pink, orange and red sunrises and sunsets to enjoy. When we see a sunrise or sunset from our perspective on Earth, sunlight is coming in at a low angle. It has to travel through a lot of atmosphere, scattering more and more blue-colored light as it goes... until what is left when the light reaches us at these day/night transition times is the more reddish wavelengths that get through."

The BBC adds, “Observers on Earth may see a Moon that is brick-coloured, rusty, blood red or sometimes dark grey, depending on terrestrial conditions."

The New York Times, in a preview to the occurrence, quoted Dr Sarah Noble, a progamme scientist at Nasa, as saying, “You’re basically seeing all of the sunrises and sunsets across the world, all at once, being reflected off the surface of the Moon."

Next appearance in 2033

Sunday’s event was the first Supermoon lunar eclipse in over three decades. The last time the two phenomena combined was in 1982. The next such occurrence is expected to be 18 years later, in 2033. Sunday also saw the fourth instance of a blood Moon in the last two years as part of the “tetrad series" or a series of four consecutive total eclipses occuring at intervals of approximately six months.

Prior to Sunday’s eclipse, the previous total eclipses occured on 15 April 2014, 8 October 2014, and earlier this year on 4 April 2015.

Interestingly, the celestial phenomenon also has religious leaders worried, with prophecies that range from “the beginning of the apocalypse" to a pastor telling The Guardian that “an event of historical significance to the Jewish people is occuring or will occur".