What Could Cause The Night Sky To Shimmer & Pulse With Light?

Hello, This morning my wife and I went to the local mountains to see the Perseids meteor shower as we often do. We arrived about 1am and both of us noticed the whole sky seemed to pulsate and shimmer with a faint light we had never seen before. We were wondering if this could be caused by the dust particles from the comet trail. It was even more noticeable with binoculars. Any suggestions would be appreciated. Thank you
Volume rendered image of a large eddy simulation of a non-premixed swirl flame. Image credit: Andreas Kempf, CC A-SA 3.0

Volume rendered image of a large eddy simulation of a non-premixed swirl flame. Image credit: Andreas Kempf, CC A-SA 3.0

Originally posted at Forbes!

There’s definitely some stuff happening to the atmosphere in the scenario you’re describing, but I doubt it’s likely to be caused by particles from the debris of comet’s tail.  The dust and pieces of grit are what you’re seeing as the meteor shower. The meteors you see during the Perseids will all seem to radiate from the constellation of Perseus, and even bits of dust are traveling so fast when they encounter our atmosphere that they will burn up quickly; but if they’re small enough, that burn may be so fast, and so faint that they may not be very bright.  But they won’t be able to make the whole sky shimmer; meteor showers must fundamentally come from one side of the planet.

The flickering and pulsing you describe points pretty strongly to a common atmospheric effect — turbulence. Turbulence appears any time the atmosphere above you is moving around a lot, and one of the more common triggers for strong turbulence is if it’s windy down near the ground, windy higher up in the atmosphere or both. Turbulence can also show up if two regions of air which have very different temperatures meet, but wind is the most common cause.

A two-dimensional, zonally-symmetric tracer advected in the Northern Hemisphere. Reference: Peter Mills (2004) “Following the Vapour Trail: a Study of Chaotic Mixing of Water Vapour in the Upper Troposphere.” Master’s Thesis, University of Bremen. Image credit: wikimedia user Peteymills, CC0

A two-dimensional, zonally-symmetric tracer advected in the Northern Hemisphere. Reference: Peter Mills (2004) “Following the Vapour Trail: a Study of Chaotic Mixing of Water Vapour in the Upper Troposphere.” Master’s Thesis, University of Bremen. Image credit: wikimedia user Peteymills, CC0

Fundamentally, turbulence is just pockets of air which are at different densities. The flickering of the starlight comes from light bending as it comes through these pockets of air, since each one can act like a little lens.  If these pockets were still, then the starlight would just be bent, and you wouldn’t notice the flickering.  But the pockets of air change shape, because the wind is still blowing, and gas isn’t a static creature, and so the light will go in and out of focus.  Blurring and then refocusing, the star will appear to flicker and shimmer in the sky.

So that explains the pulsing, but not the faint sky glow you’re describing. There are a couple options here; the first is that there was some light pollution from the town nearby, but you might have noticed it seemed brighter in the direction of the town than back towards the mountains.  Possibly not, though — it depends on how isolated your mountains are, and how far away from town you were.

Night sky (stars and the Milky Way), Cherry Springs State Park, Potter County. Image credit: Nicholas A. Tonelli CC BY 2.0

Night sky (stars and the Milky Way), Cherry Springs State Park, Potter County. Image credit: Nicholas A. Tonelli CC BY 2.0

Another source of faint light can be the Milky Way – but it doesn’t sound like that was it, because the Milky Way would have been a band of brighter light going across the sky, and often looks more like high clouds and fuzziness in the sky than a glow across the whole sky.

It’s also possible that the sky shimmering with extra light is the turbulence coming back to play again — as the light from the stars in your mountains’ sky blurs in and out of focus, your eyes will pick up on the flickering brightness of the individual stars, but as the stars go out of focus, it’s possible that your eyes will interpret that as the sky itself glowing in exchange.

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Do stars really twinkle?

A very silly question but many as for as I know just consider this as default and force it into their mind without knowing reason!! Do stars really twinkle? If really yes, then why ? Or is it because they burn and hence it appears like they are twinkling.

Not a silly question!

If you go outside on a clear, windy night, and look up, you should be able to see the stars twinkling their hearts out. Or if you’re in an area where you can see down close to the horizon, even if the stars overhead don’t seem to twinkle, the ones down lower might seem to flicker.

On the other hand, if you go out on a clear, still night, and look at the same stars, you should find that they hang quietly in the night sky, not a twinkle to be spotted.

The twinkling is entirely the result of our atmosphere being a bit of a mess. As the light from a distant star reaches the earth, all of the light is well aligned, and if you were to observe the stars from space, you would see them as perfectly point-like pricks of light. However, the atmosphere can quickly distort that alignment. Pockets of air which are slightly warmer or colder than their surroundings will bend the light a miniscule amount, but enough to spread out the light over a slightly wider area. As the light passes through our atmosphere, hitting more and more pockets of air, the starlight gets more and more bent out of shape, into weird, non-point figures.

The atmosphere is also constantly changing - the image above is a series of images taken by William C. Keel, at the University of Alabama, with only a second’s wait between images. (Each image is about 1/100th of a second long.) You can see how dramatically the images change between seconds - without the atmosphere, each of these images should look like a single dot of light.

For astronomers, we describe this atmospheric distortion as “seeing” - the better the seeing, the less twinkling the stars are doing. The twinkling of stars is actually a huge problem for astronomical data, because it’s really hard to get really clear pictures of space, when the atmosphere is making everything do this:

This is one of the biggest reasons that we like having telescopes up in space - we can get around the pesky atmosphere of ours. But it’s not something the stars are doing - if the stars are twinkling it just means that our atmosphere isn’t very stable that night.

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