Fireball over Iceland | Hacker News Reader

Fireball over Iceland

apod.nasa.gov

210 pointspolitelemon43 comments

The video shows northern lights for the most part. I like that it's a video and you can see people move stuttery/stop-motion. Typically, northern lights are posted as picture and you have no idea what it was really like irl. I saw it once in Finland and thought it was clouds very faintly moving against the night sky. "Too bad," I thought, "if there were lights then this obscured them". The next morning I saw pictures where it looked like the most spectacular thing: those "clouds" were northern lights! Here at least, it's obvious that the exposure time per frame is cranked up because we don't perceive people as stuttering during the night.

(Later I saw the lights properly in Iceland, but it was still just a faint green haze. Can be mistaken for city glow at a glance, but if you look for a bit it becomes clear that it's moving slightly and too green. Again less than what one might be lead to expect)

That's not always the case. I saw them in Iceland and yes, they were faint one day (such that only my camera could see them), but another day they were really bright, and they looked like waves in the sky, changing very quickly. It depends on the day.

Sorry mate, but you did not see them properly. In February, we had some that looked like in the video to the naked eye. And I was in the outskirts of Stockholm, so neither that remote nor that far north. Obviously doesn't happen that often, though the locals weren't bothered much.

I know it gets better than what I saw in general, but this was about three months of being in Finland and Iceland cumulatively (both times during fall). Figured that's the best most people can hope to see, at least without specifically going very far north at the right time of year for this specific purpose, and so the pictures just aren't representative of what you are likely to see while in these countries

>Figured that's the best most people can hope to see(...) so the pictures just aren't representative of what you are likely to see while in these countries

Its quite wrong to assume your three month experience is representative for what you would expect to see of northern lights in Iceland and Finland.

I don't think most people's holidays are going to be longer? Not sure what makes you say that. I understand one might get lucky or unlucky, are you saying my 3 months happened to be extremely unlucky and therefore it's "quite wrong" that this can be extrapolated to an average experience when visiting the countries?

There's probably a big difference between what you could see under ideal circumstances, and what you're likely to see during a normal vacation.

I live in Winnipeg, way south of Finland, and I've seen spectacular northern lights not far from here.

Really? Isn't Winnipeg only 50 degrees north? That's south of Amsterdam, and we can absolutely never see northern lights here. It's something for which you need to go to northern Scandinavia.

Yup. It also gets down to -40 in the winter.

I'm less surprised about that. Land climate and no warm gulf stream makes for a totally different climate. But I didn't expect the northern lights to be ruled by temperature.

I think it is more ruled by the earth magnetic field. And as the magnetic pole is closer to north america, you have them further (geographically) south there.

That's a lot more likely. Magnetic North is 80 degrees north rather than 90, and in Canada, so if you can see the northern lights at 50 degrees there, that would be comparable to 60 or 70 degrees elsewhere.

Patall is right, I was just pointing out another surprising winter-related fact. But it's not surprising if you understand weather systems.

I'm in Amsterdam and I can't even see the stars at night, but in Stockholm they get this and don't even care?

They always look better in pictures. Even a cheap camera phone will take a good picture of them.

Don't go into the trap to think that all northern lights are that faint. Iceland are pretty far South in many ways, in addition the intensity varies. Sometimes it is just spectacular, a lot more spectacular than on pictures.

I've seen the northern lights once before with my own eyes and no you cannot mistake them for "clouds" or "city lights". You unfortunately probably saw a very faint version, probably low to the horizon.

And no I wasn't even in the far north. It was during a solar storm and I was in my own backyard in southern Michigan.

Aurora that looks grey is simply too feint for your eyes to perceive the colour[0][1]. One way you can confirm whether what you're seeing is aurora or not, is to take a picture with a digital camera. Camera sensors can discern the green (or whatever) hue, whereas the cones (which perceive colour) cannot pick up such dim light.

Once the aurora becomes stronger, you can absolutely see shockingly-vibrant green, pink, purple, and other colours, literally streaming/swirling/dancing across the sky. It's an unforgettable experience. I hope you have the chance to see this at full-strength sometime, and I absolutely recommend seeking it out if possible. (extra-recommended to watch while sitting in an outdoor hot tub at midnight in -10*C in Iceland, of course!)

[0] https://www.neworld.com/blog/2018/aurora-borealis-and-our-ey...

[1] https://futurism.com/how-we-see-the-aurora-borealis-camera-v...

Sounds like they were just about to pack up and leave, and then this happens. Spectacular, and incredibly lucky that they got to see it like that. Not to mention those northern lights look great. I should go to Iceland some day.

1:06 - what is moving in the top right quadrant of the video amongst the stars?

Probably a satellite in low-earth orbit. They only take a few minutes to go from one horizon to the other. Since it is very bright, I am guessing it is the ISS.

Update: Iceland is too far north (64°N) to see the ISS (max 51.6°N). Too bad.

Was about to say, northern lights are not in the south as seen from Iceland so ISS would not be probable. It should be possible to figure out what high-inclination object was in the sky at the right time of day (it needs to reflect sunlight) on September 13th as the video description says it was shot on

Edit: or based on the fireball timing, mister detective here just realised. The comments even say "Is it possible that it was on 12.09.2023 at 22:35? We were in Höfn watching the northern lights when we saw it" and a reply confirms it

Why does the fireballs tail persist in the sky?

Is this some type of long exposure video setup?

Even after reading the FAQ (which is excellent: https://www.amsmeteors.org/fireballs/faqf/) I'm not quite clear why a meteor would be a fireball versus not being one. Is it simply about size, or something in the composition?

It is just about the brightness. Answer number 1 in the FAQ states:

> A fireball is another term for a very bright meteor, generally brighter than magnitude -4, which is about the same magnitude of the planet Venus in the morning or evening sky. A bolide is a special type of fireball which explodes in a bright terminal flash at its end, often with visible fragmentation.

Or was your question why are some so bright? That is mainly a function of size and speed.

Could it also be composition? eg. Mainly water vs mainly rock vs rock with particular metallic impurities?

Meteors are very small. The bright light comes mostly from the molecules of atmosphere in front of the meteor being compressed, heated, and ionized[0] - essentially from the friction of the high-speed meteor entering the atmosphere.

I guess if the meteor was a ball of pure magnesium, it might glow brighter, but there isn't so much oxygen up at that height, so my no-calc-gut-feel estimate is that this would contribute orders of magnitude less brightness than the glowing atmospheric molecules.

[0] https://www.amsmeteors.org/meteor-showers/meteor-faq/#3

To the extent it's about composition it's probably mostly about how long the meteor holds together so it can retain velocity and the surface can stay hot enough to glow. A bunch of small pieces decelerate faster than one big piece. Compositional changes would only change the color somewhat but likely not enough to be worth commenting on.

Mostly size. Ordinary shooting stars are grain-of-sand sized, and what you see is actually the superheated air that they displace coming in at 10+ km/s. Something slightly bigger, like a rock a few cm wide, can cause a blinding fireball.

Speed also counts. It can range from 8 km/s (a "stationary" object, relative to us, falling into Earth's gravity well) to about 70 km/s (something in a retrograde orbit in the Earth's plane). That's a factor of almost 80 in energy to be dissipated

From Britannica:

> Meteors are the result of the high-velocity collision of meteoroids with Earth’s atmosphere. A typical visible meteor is produced by an object the size of a grain of sand and may start at altitudes of 100 km (60 miles) or higher. Meteoroids smaller than about 500 micrometres (μm; 0.02 inch) across are too faint to be seen with the naked eye but are observable with binoculars and telescopes; they can also be detected by radar. Brighter meteors—ranging in brilliance from that of Venus to greater than that of the full Moon—are less common but are not really unusual; these are produced by meteoroids with masses ranging from several grams up to about one ton (centimetre- to metre-sized objects, respectively).

I think if you consider light pollution around populated areas and the fact that most people don't spend much time looking at the sky carefully, most of the shooting stars actually noticed by most people are larger than sand, probably more like tiny gravel than sand.

Would like to know what time this happened - I was in Iceland looking up at the sky that night, but didn't see the meteor.

22:35, presumably Icelandic timezone because the comment (at https://youtu.be/GHHitRCagcE) containing this timestamp says "We were in Höfn watching the northern lights when we saw it"

Great, thanks. Sad I just wasn't looking up at that time.

How big would such a meteor be, more or less, to generate such glow? Is there a way to estimate it?

One metre does it

I saw this one from 500km away and it was easily the most impressive thing I've seen in my life: https://en.m.wikipedia.org/wiki/2023_CX1 It says that was 1m in mean diameter, but also weighed 1Mg, which seems like a lot but when I look it up, a spheric m³ of aluminium is already heavier than that (1.4Mg) and iron would be 3× heavier still

Writing mass in megagrams is positively badass!

It's what my calculator outputs, and 1kkg or writing 1000 before the kilo prefix both felt a bit silly

In a peer comment's link to the video, the videographer estimates this one was the size of a tennis ball. A typical meteor you might catch out of the corner of your eye on a dark summer night is the size of a rice grain.

That’s bonkers

Good old p=mv. And that v can be pushing 70 km/s thanks to the combined motion of the Earth and the meteoroid.

10 meters was the size of the Chelyabinsk meteor which caused significant damage on the ground from its air burst. I’d guess significantly under that size then since this doesn’t appear to have done anything other than make a pretty light.

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