Early risers on Friday will be treated to the spectacle of the moon turning blood red as it drops towards the horizon.
The celestial display is due to a total lunar eclipse, an astronomical event that last occurred back in November 2022.
It will be visible in Irish skies from 5.10am and peak in intensity at about 6.20am.
The Earth orbits the sun, and the moon orbits the Earth. When the sun, Earth and moon are lined up in space so that the Earth blocks the sunlight from hitting the moon’s surface, then a total lunar eclipse occurs.
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During a full moon, the sun normally lights up the surface of the moon, which then appears white, but when the Earth passes between the moon and the sun during the full moon, the result is a total lunar eclipse as well as a blood moon.
“The moon is going around the back side of the Earth and the Earth is blocking all of the sunlight,” said Dr David Long, assistant professor in solar physics in the School of Physical Sciences at Dublin City University.
During the lunar eclipse, not all sunlight is blocked from hitting the moon, however, because if that was the case it would not be visible.
Some light does get through, said Dr Long. This light reaches the moon, and then is reflected back to Earth.
“What’s happening is that light is passing through the atmosphere, but the shorter wavelengths – yellow, green, blue – get scattered away.
“The longer wavelengths – orange and red – are able to continue through then this gets reflected off the moon.”
As a result of this light scattering, we see the moon as ‘blood red’, because when this sunlight hits our atmosphere the atoms and molecules of gas in the air absorb the light, then scatter, or re-emit, it out in all directions.
The intensity of red seen from Earth is also due to amount of dust and pollution in the atmosphere because these both increase the scattering effect.
The more dust and pollution in the atmosphere, the redder the moon appears.
“If the atmosphere doesn’t have a lot of dust in, you don’t scatter as much so it appears kind of orangey,” said Dr Long, “So, how strong the blood moon is depends on how clean the Earth’s atmosphere is.”
The redness can also be affected if a lunar eclipse happens shortly after a volcanic eruption has taken place somewhere on Earth. An eruption, particularly a big one, will mean more dust and projectiles will be present in the atmosphere, making the blood moon appear even redder and darker than usual.
The Earth is the only planet in the solar system to have total lunar eclipses, because it casts a big enough shadow to cover the moon. There are two to four lunar eclipses per year, and each one is visible over about half the Earth.
The visibility for this blood moon is best in the northern hemisphere, and in particular North America. In Ireland we will see part of the event, because when it reaches its peak of intensity the moon will have dropped below the horizon.
Unlike a solar eclipse, which involves not looking at the sun, no special protective eyewear is required to view the blood moon, as we are looking away from the sun, and towards a moon shadowed by the Earth.
