Why Are Shooting Stars White?

[Chesterton]

Unexpectedly, I got to see several shooting stars in the predawn hours this morning. Why do they appear to burn white, and not yellow like flame? I found an article that says they can burn other colors depending on the minerals in the rock, but I've seen many in my life and never seen anything but bright white light.

 

[yeshuaslavejeff]

The article you read was correct.

 

[HatedByAll]

Part of it is the intensity of the light. Many times with a normal sized meteorite, you are seeing something that is quite small but it appears larger. For example, you may be seeing something the size of an orange from miles away. The point of entry into the atmosphere is 64 miles up and when the meteorite starts to burn is shortly after it reaches earth's atmosphere. I don't know when the object would ignite, but it is likely at least 5 miles away and likely even as far as 40 or 50 miles away. Just think, if you saw a regular sized light bulb that was visible from that far away, how bright it would be. When you are seeing white, what you are seeing is overexposed.

When taking a photo, if a red or blue or any color light is in the image and the rest of the image is darker, the light will be overexposed if you set the exposure for the rest of the image. That light will just look white. Seeing a meteorite is the same principle.

 

[Strathos]

I saw an orange one once.

 

[sjastro]

I once observed a bolide which was brighter than the full moon and had a greenish colour probably due to an iron-nickel meteor.
The bolide broke up into a number of fragments each leaving a trail in the sky and was accompanied by a thunderclap sound.

 

[essentialsaltes]

I can't say I've ever seen a meteor with any noticeable color. A little googling suggests that colors are more associated with fireballs/bolides as in sjastro's story. They tend to be much brighter, so I wonder if the difference is just that our color receptors (cones) are not as sensitive as our light receptorrs (rods). So fainter meteors are necessarily uncolored to our vision.

 

[chilehed]

I've seen white, yellow, orange, blue and green. It really does depend on the composition of the meteor, as well as ambient light levels and how well your eyes are adjusted to the dark. It also helps to have done a lot of meteor watching.

 

[chilehed]

I once observed a bolide which was brighter than the full moon and had a greenish colour probably due to an iron-nickel meteor.

Wow, that's a great one, you're very fortunate to have seen something like that!

One night we saw a really big, slow (by meteor standards) blue-green one that went for a long way, well over fourty-five degrees. We all all looked at each other and in unison said "dropped wrench".

 

[timewerx]

I've seen fast deep reds a few times. Ferrari red hue.

Greenish or bluish whites are most common. I think this is more likely to the extreme heat driving incandescence to the "white-hot" bluish region, regardless of the material the meteor is made of.

 

[Michael]

Unexpectedly, I got to see several shooting stars in the predawn hours this morning. Why do they appear to burn white, and not yellow like flame? I found an article that says they can burn other colors depending on the minerals in the rock, but I've seen many in my life and never seen anything but bright white light.

Over my lifetime I've seen a few green ones, and some red/orange ones as well. It does depend on the minerals in the rock, but I suspect that a lot of them emit many colors which our eye simply register as appearing to be "white hot".

 

[LiquidCat]

Unexpectedly, I got to see several shooting stars in the predawn hours this morning. Why do they appear to burn white, and not yellow like flame? I found an article that says they can burn other colors depending on the minerals in the rock, but I've seen many in my life and never seen anything but bright white light.

Because that's how angels looks like they appear like light and mostly we see it as white.

 

[Chesterton]

I just saw a brilliant green shooting star, with some gold and a long white tail. Got to watch it for maybe a good three seconds. I remembered this thread and thought I'd bump because - neat-o!

 

[Bob Crowley]

I suppose we might occasionally see a meteor with a different colour, but i think most of the time we're actually seeing the trail of glowing hot air behind it, which would appear to give off a range of mixed colours aka "White".

We don't actually see the rock itself, unless we've got rather advanced telescopic and photographic gear (and even then I don't know if we could actually see the meteor unless it was a big one).

Overview | Meteors & Meteorites – NASA Solar System Exploration

A meteor is a space rock—or meteoroid—that enters Earth's atmosphere. As the space rock falls toward Earth, the resistance—or drag—of the air on the rock makes it extremely hot. What we see is a "shooting star." That bright streak is not actually the rock, but rather the glowing hot air as the hot rock zips through the atmosphere.

 

[Subduction Zone]

I would think that it is because color is an indicator of temperature. They are not "burning" in the sense that wood burns. The color is not due to the oxidation of the meteorite. The color is due to it heating the air as it plows through the atmosphere at extremely high speed. Okay, I had to look this up to get some specifics:

Fireball FAQs.

The speed of a meteoroid through the atmosphere ranges from about 11 km/sec to 72 km/sec (25,000 mph to 160,000 mph)! At that high rate of speed it instantly heats and bits are torn off as molten material. That is extremely fast and the outside of the meteor gets very hot. Since the material is also ripped off of the meteor in the process it does not heat up very much so they can still be rather cold when they land.

 

[Astrophile]

Unexpectedly, I got to see several shooting stars in the predawn hours this morning. Why do they appear to burn white, and not yellow like flame? I found an article that says they can burn other colors depending on the minerals in the rock, but I've seen many in my life and never seen anything but bright white light.

I have seen a red meteor. Unfortunately I didn't make a record of it. So far as I can remember, it was fairly bright and had only a short path.

 

[chilehed]

That bright streak is not actually the rock, but rather the glowing hot air as the hot rock zips through the atmosphere.

I'm not buying that.

 

[Chesterton]

I'm not buying that.

But the NASA quote is talking about the "tail" behind the rock, isn't it?

 

[chilehed]

But the NASA quote is talking about the "tail" behind the rock, isn't it?

I don't read it as meaning the afterglow and wake and not the meteor itself, but in any case I think it's just flat-out wrong. Otherwise the observed color wouldn't be affected by the composition of the meteor (which it most certainly is), nor would the length of the afterglow. There are slow meteors with very long trails, and fast moving ones with short trails, and that wouldn't be at all possible if the appearance of the trail wasn't largely a function of what the meteor is made of.

That piece also implies that meteors get hot because of air friction, which is absolutely false. They get hot because of the stagnation temperature of the accelerated air at the leading surfaces of the object. It's not friction at all, it's adiabatic compression of the airstream.