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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How Come I See Fewer Stars Than I Remember As A Child?

I’m past eighty years old. I remember as a child the stars looking like they were almost on top of us, so close and so bright and a billion of them to boot. Now they look so far away and almost faint. No it is not my eyesight. Have the stars moved away from us to that extent in just 80 years and if so how long before they are not seen at all.
The constellation Orion, imaged at left from dark skies, and at right from Orem, UT. Orem, UT is hardly a large city. This is intended to highlight the fact that light pollution is a problem everywhere, not just in cities with tens of millions of inhabitants. Image credit: Flickr user jpstanley, CC BY 2.0.

The constellation Orion, imaged at left from dark skies, and at right from Orem, UT. Orem, UT is hardly a large city. This is intended to highlight the fact that light pollution is a problem everywhere, not just in cities with tens of millions of inhabitants. Image credit: Flickr user jpstanley, CC BY 2.0.

Originally posted at Forbes!

Unfortunately, the stars haven’t moved, and I believe you that it’s not your eyesight either, because there’s another known and astronomically obnoxious thing that’s happened over the past decades. The amount of light pollution in the night skies has increased dramatically in the past few decades, which is largely because there are a lot more lights, illuminating our cities with no particular care for the darkness of the sky.

The increase in lighting is generally a good thing – well lit streets make people feel safer walking at night, for instance. However, the typical streetlight sends a lot of light up into the night sky, and not just down onto the sidewalks and streets. We also do a lot more lighting up of entire buildings now than we used to, several decades ago, and that light reflects off the building into the night sky. With the advent of cheap, bright LEDs, many of these lights are getting even brighter.

Marina Bay Sands, Singapore, at night. Singapore’s light pollution is so severe that the entire population will never use their night vision. Image credit: Leonid iaitskyi, CC A-SA 3.0.

Marina Bay Sands, Singapore, at night. Singapore’s light pollution is so severe that the entire population will never use their night vision. Image credit: Leonid iaitskyi, CC A-SA 3.0.

The combination of all the streetlights, spotlights, and building lights work together to fade our night sky. The more light pollution there is, the less black the night appears – the sky will only darken to a gray – and the more light pollution, the fewer stars are visible.  The faintest stars fade out rapidly, and relatively soon, there are only a few stars which remain.  

If you make it out to a truly dark spot, the stars of your childhood are still there – literal thousands of them, filling the night sky. But many people who live in cities have no way to get out to see the night sky in a remote area, so the dark, glittering sky is either a distant memory or feels like an experience they will never get to grasp.  This isn’t uncommon. It’s now estimated that 30% of the world’s population cannot see the Milky Way from their homes. This goes up to 80% if you live in North America.

We could make some improvements – the loss of the Milky Way doesn’t have to be permanent. We could choose to not illuminate the sky quite so much while we continue to light the streets for safety reasons.  Shielding the light so it can really only shine down would be an easy first step.  Switching off the lights that light up an entire building – even for a few hours in the middle of the night – would help any would-be meteor shower watchers getting up to watch the sky.  Any improvements we can make will bring the night sky back to everyone.  In the mean time, we’ll have to push for more lighting improvements, so that the only dark skies aren’t just in remote wildernesses.  If you’re ever in a dark area, far from a city, remember to look up.

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