The total lunar eclipse will envelop the full moon in a deep red glow on the night of July 27th.
During the eclipse, the moon is expected to dip for an hour and 43 minutes – the longest total eclipse for at least another 82 years.
The Royal Observatory Greenwich astronomer Dhara Patel told Express.co.uk there are a number of explanations for why this happens.
The space expert said, "There are actually several reasons why this happens, when we think about the shadow behind the earth caused by sunlight, that shadow is what the moon goes through.
"We can imagine that it's like a circular region in the sky and sometimes, if the moon does not go right through the central part, it will move to the edges of that circular shadow.
"This time the moon goes through the central part of this shadow instead of flying over it down or up.
"That's one of the reasons why the eclipse will be longer and another is the moon's point."
The orbit of the moon around the planet is quite irregular and elliptical than perfectly round.
Eclipse 2018: The Bloodmoon will be the longest lunar eclipse of the century
Due to this irregular orbit, the average distance of the moon from the earth is extended and shortened depending on its potion in the sky.
During the July Eclipse, the Moon is at its farthest position from Earth – the so-called Moon Apogee.
Ms. Patel said, "What we'll see is a seemingly smaller moon, and because it's farther from Earth, it will travel a little slower.
"These two things mean we will see a longer solar eclipse, as it takes longer for the moon to pass the shadow of the earth.
"One last thing is that Earth's orbit around the Sun is also not perfect, it's an elliptical orbit, and during the summer the earth is in its furthest orbit from the Sun – it's Aphelion.
1 from 43
"During this time, the shadow behind the earth is slightly longer and wider due to the angles between the sun and the earth when the earth is a little further away.
"That means the moon needs a bit longer to pass through the shadow."
In the UK, the initial phase of the lunar eclipse will begin as soon as the moon rises above the horizon.
This means that the moon should already be red or just red at moonrise.
The partial solar eclipse of the Blood Moon begins at about 7.24 BST below the horizon, followed by the so-called total eclipse phase between 20:30 and 21:00 BST.
Eclipse 2018: The blood moon turns red because of the scattered sunlight in the atmosphere
The Bloodmoon will hit the maximum eclipse or solar eclipse at 9:20 pm.
This time the moon goes through the central part of the shadow
But why exactly does the full moon become blood red during the total lunar eclipse?
Ms. Patel explained, "The moon orbits the earth, and when the moon passes directly behind the earth in the shadow of the planet, we see a lunar eclipse on the opposite side of the earth compared to the sun.
"Usually, when the moon is in that position, you would expect no sunlight to reach it, so you would expect it to be completely dark.
"The reason it takes on this reddish hue is that the earth has an atmosphere and when the sunlight reaches the atmosphere, gases in the air actually scatter or bend the light, and it's red light that's just in the right amount is scattered is finally directed to the surface of the moon.
Eclipse 2018: The Bloodmoon will be visible from across the country this month
"During a lunar eclipse, when the moon is in the shadow of the earth, the atmosphere causes the red light to bend towards the moon, and that's why we see this reddish color and people call it a blood moon."
The lunar eclipse will be visible from the moonrise to around 10:13 am BST when the total eclipse ends, from across the UK.
Moonrise times all differ by a few minutes from place to place, so check your local times before the eclipse.
By midnight, the full moon should return to its normal white glow high above the horizon.