Asteroid nearly gave Earth a new feature, two days after its discovery On Saturday, the Catalina Sky Survey spotted a near-Earth asteroid of respectable heft – and today, it passed between us and the Moon. 2017 AG13 (the Minor Planet Center, MPC, entry is here) is about the size of a 10-storey building. Its velocity to Earth is 11 kilometres per second. It passed at 0.53 Lunar distance, or 203, …
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Mostly we see them _after_ they've gone past.
This has a lot more to do with them coming from the direction of the sun (lit from behind, so virtually impossible to see) and being lit up as they go past us than their dimness.
The moon is about as black as a piece of coal. Most of these rocks are somewhat duller than that.
source?
The surface of the moon is mostly described as light grey. The moon's albedo is ~0.1 whereas coal has a much lower value ~0.05.
If you are comparing snow, coal and the moon maybe you could say "the moon is about as black as coal" but without context I think your statement would be misleading for most people.
To be fair you could probably specify a hemisphere...
I mean - one side of the earth was facing in the direction from which the asteroid came at the time it passed by - so I reckon that hemisphere was more 'at risk' than the other...
But yes - it's like asking which section of a tennis court the basket ball would land in if bowled from between the posts on a rugby pitch.
Íf it'd had hit Earth's atmosphere it would most likely not have hit at all.
Note the comparison to the Chelyabinsk rock... At that size meteors don't burn up, but disintegrate/explode midair.
It's what you get with Youth.. Not patient enough to wait until they touch down and make a nice crater.. Noooo.... They have to do the whole "You don't need Nukes to make a Big Bang" right away.. **
** No... I deny any science here... This is the celestial Youf , Showing Off , playing chicken with the older bigger kids, and occasionally failing to miss.
"At that size meteors don't burn up, but disintegrate/explode midair."
If the angle is shallow, yes.
Chebalinsk skimmed through the atmosphere for several hundred miles before breaking up.
On a steeper angle the airburst can bring a supersonic shockwave of superheated air to the ground.
if you have a lot of rocks, this can result in a very bad day (hot enough to melt surface rocks, resulting in a volcanic appearance without any nearby vulcanism - and there are a few places on the planet like this) - one researcher by the handle of craterhunter has been advocating this as a possible cause for the sudden extinction of north american megafauna and the younger dryas periods. Some of the supporting evidence is quite compelling, in particular "recently" melted surface rocks in southern North America with no supporting igneous activity.
I looked at craterhunter's site, and I can say as a Google Earth monster that the 'crater' image he has on that page does appear to the untrained eye to be a blast site, but in fact is typical desert erosion that just happens to be arranged to look kinda radial in pattern.
Of course, I did have to find the site on Google Earth to be sure, and craterhunter neglected to provide a link or info. And it does look like his photos are a bit doctored to make the 'crater' stand out a lot. I've spent many years living and hiking on just such terrains. They're everywhere in the US Southwest, and that site shows a caprock layer around the edge of a bowl with erosion proceeding into the soft layers below the caprock. It's extremely typical of the desert here.
In short, cool as it sounds, I was not impressed with the "ancient airbursts killed the megafauna" theory based on that proposed location. Don't have much to say about other evidence, but I'd guess he's a bit of a kook. A fun one tho!
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No, Bruce can't help us now. Getting kinda long in the tooth. We need new heroes, men and women (and others) who will place their fragile bodies on the line for their planet. 'Git 'er done' types (like Bruce) who don't flinch when flipping the Nuke Gun lever to 'Auto.'
Um, is Chuck Norris still available...?
In science velocity is a vector and thus including a direction. However according to the dictionary it can simply mean speed. So I think it is one of these instances where a field of study has taken two words that mean the same and added a distinction that wasn't there, before they go out and pester people that actually use it correctly. (I don't actually know the historical development of this word though)
Interesting. The distinction felt artificial to me, then I just realized neither of the other two languages I speak (one of latin origin, one not) has different words to designate speed vs. velocity. Sure, there are a bunch of more or less synonyms, but as far as physical properties are being described, both have only one word for both the scalar and the vector...
If I remember my A-Level and university maths, what a vector represents is dependent on the number of dimensions you're working in.
If you are working in one dimension, a vector and a scalar are the same thing. In two dimensions (the standard environment when you are learning vectors IIRC), a vector is normally described as a one by two array in a cartesian co-ordinate system, or a scalar and an angle in a polar co-ordinate system.
In three dimensions, a vector will be a one by three three array in cartesian, or a scalar and two angles in polar co-ordinate system.
I'm sure that some theoretical physicist or mathematician will point out that they work in more than three dimensions!
So the upshot of this is that if you are working in one dimension, taking the path of the asteroid as a dimensional frame of reference, the velocity, even if treating it as a vector can be considered the same as it's speed, and this is what most lay people will count as a velocity.
Of course, celestial mechanics is never that simple, and is normally in at least 4 dimensions.
Ummm.... no.
A scalar is dimensionless.
A vector has dimension(s), and is expressed with respect to a co-ordinate system or systems, as it has a direction as well as a magnitude. It can be represented as an ordered n-tuple, which itself has one dimension, where n is the number of dimensions represented by the co-ordinate system.
In common English, I would say that speed has an "absolute" quality to it; even though speed/velocity can never be truly absolute, people have a notion of a stationary position and therefore an absolute speed.
Saying "it's speed relative to Earth" is fine, but just doesn't sound quite right. "It's velocity relative to Earth" is much better.
Quite. It's common knowledge the only thing we really need to fear (well, beside "fear itself") are high-altitude Nokias...
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