La luna de sangre

Given that this is a blog by an astrophysicist originally meant to report on ESO-based life events, there have been more posts about me going on my jollies than there have been about spacey type things. While everyone loves a photo of a penguin or a super-awesome view, I thought I would sprinkle a little science over your day.

In April, we in South America were lucky enough to be in prime position to witness a total lunar eclipse – an event that happens around 1-3 times a year and is visible from different places across the globe. As you well know already, our place in the Universe is pretty unique and special, and our position in the Solar System even more so. Asides from taking up much sought-after real estate in what is known as the ‘Habitable Zone’, or ‘Goldilocks Zone’ (where conditions are neither too hot nor too cold, but are ‘just right’… see what they did there?), it just so happens that everything in our night sky is positioned so nicely as to make our Sun and moon appear exactly the same size when seen from Earth. The Sun is about 400 times the size of the moon in reality, but is also found 400 times further away from the Earth. This is why during a solar eclipse the moon can pass in front of the Sun and appear to cover it perfectly, temporarily preventing its light from reaching Earth and thus plunging us into darkness for a few creepy minutes.

Lunar eclipse - just a result of simple geometry!

Lunar eclipse – just a result of simple geometry! Image taken from:

A lunar eclipse, on the other hand, occurs when the moon passes behind the Earth in such a position that it finds itself totally in its ‘shadow’ – also known as the umbra – as these three celestial bodies line up. This lining up is also known as a  ‘syzygy‘. So it would be a little like witnessing a solar eclipse if you were stood ON the moon, but this time with the Earth blocking out the stellar light.

Because Earth’s umbra is obviously a lot larger than that cast by the moon during a solar eclipse, a lunar eclipse lasts several hours from start to finish instead of the solar’s few minutes as this is the time it takes the moon to move out from the shadows and fully back into the light. About an hour and a half of this time is spent in ‘totality’, i.e. the best bit of the show where the full moon turns blood red – otherwise known as ‘la luna de sangre’ in Spanish.

Pre-eclipse full moon at twilight (real twilight, not the gay vampire movie).

Pre-eclipse full moon at twilight (real twilight, not the gay vampire movie).

Moon entering the eclipse

Moon entering the eclipse…

La luna de sangre, taken by  moi at Paranal

… Tadaa! Blood moon.

But why does it turn red? Well, this is thanks to Earth’s atmosphere, which bounces around light from the Sun as it passes through. The bluer colours of the light are filtered out, meaning that the remaining redder light is refracted onto the Moon’s surface. If Earth had no atmosphere, then the light couldn’t undergo this filtering and refracting process and the moon would actually appear totally black and invisible! Lucky for us that this isn’t the case, as it would make for some pretty boring pictures (and we couldn’t, you know, breathe and stuff either, but I feel that’s by-the-by in this conversation).

So that’s the basics of what happened on April 15th of this year, and by pure coincidence I was up at Paranal (with Oscar again, yay!) being trained on how to attend to special visitors as an ePOD representative. So on that night, we had two French guys who worked for a planetarium and had come to take images and videos for a new planetarium show. They were also very happy that it coincided with the eclipse, and I’m sure it gave them an extra edge for their project!

So we all (myself, the two French guys and my colleague, Laura) got to spend the duration of the eclipse up on the Paranal platform – the bit where the VLT units are located. It’s amazing how cold you can get from standing around for a few hours rather than the usual five minutes you normally spend outside at the observatory, so I was LITERALLY wearing everything I had brought with me! T-shirts X 2, jumpers x 2, ski jacket, leggings (part of my PJs!!), socks x 2, my silly Chile hat, a scarf and gloves. Even then, I still had to periodically nip back into the control room to grab a cuppa to warm up!

But yeah, a few cold tootsies were well worth what I got to see. As it was a full moon, the platform was lit up – you could see everything perfectly clearly, and we even cast an extremely well-defined moon shadow onto the ground! I had just bought a new camera, so was very happily playing around trying to get to grips with it (all photos in this post were taken by me). I set a long exposure shot for about 30 seconds, and the resulting image came out like it could have been in the day!

The only giveaway that this was taken in the middle of the night are the stars...

The only giveaway that this was taken in the middle of the night are the stars…

Then the eclipse started. As the moon got further and further into the umbra, the sky got darker and darker and the stars began to pop out. Totality hit, and the desert night sky I have come to know and love finally made its appearance. The central band of the Milky Way, our home, became visible in all its glory, showing off its dusty lanes and distinct orange glow. I will NEVER get bored of that view, my jaw drops every time and I get a horrific crick in my neck from looking up for a solid two hours, unwilling to peel my eyes of it. The odd shooting star (or meteorite, to those less romantic astronomers!) went streaking through one side of the night sky with the blood red moon on the other and our Galaxy above. Brilliant.

Moon enters totality, the Milky Way starts becoming visible (taken with a long exposure)

Moon begins to be eclipsed, the Milky Way starts becoming visible (taken with a long exposure)

What appears during totality. Not bad,

What appears during totality. Not bad.

During the full moon

During the full moon

During the eclipse!

During the eclipse!

The next lunar eclipse is not due to happen until 8th October this year, visible around the Pacific region. If you hear of any occuring in your part of the world at some point in the future, PLEASE go and watch it! So often our poor little moon is pushed to one side as being a “boring” bit of astronomy because it is so well studied. But big things often come in small packages, and in a dark place a lunar eclipse can certainly offer you a big view of how incredible our place in space is.

Hasta la proxima,


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