I saw this once. It was quite a few years back, through my 8" dob in my front yard. I saw a flash and couldn't imagine what it could have been except an impact.
After some research online that night I began to doubt myself, most people concluded it was too rare and would not be visible.
The next day I saw someone asking in a newsgroup about the mysterious flash he had seen the night before while observing the moon through his telescope. Again, the general consensus was that he couldn't have seen an impact, it was too rare and would not be visible.
I checked with him and we both saw the flash at the same time.
I also saw a satellite transit the moon once with that same telescope, it was so cool.
And to think I don't even pull it out anymore. Sad....
Just wanted to say that I helped build this site. It's 2009/2010-era Django site built on feincms with a PostgreSQL backend.
Originally it was a Plone site but after a year we realized it was too hard to meet the deadlines of NASA VIPs. So we moved it to Django. Also, myself and the other developers have NEVER been happy with the flash on the front page. :P
I would be remiss in not thanking the Varnish cache developers, too: it's using CloudFront now but Varnish came in quite handy when we suddenly jumped from mostly images to some large videos like http://science.nasa.gov/science-news/science-at-nasa/2010/21... shortly after launch.
The scariest bit of code was probably the scraper + html5lib normalizer I used to migrate something like 15 years of legacy static HTML content from two separate into the CMS using a large pile of selectors and cleanup heuristics.
One open-source tool which came out of this was https://github.com/shentonfreude/webcompare which we used to bulk-compare the old and new sites to confirm that all of our legacy URLs either redirected or were intentionally 404/410ed.
Thanks for speaking up! FWIW, you did most of the work for the migration and rebuild. I apologize for not naming you when most of this was your work. :-)
To some this might come off as simple bragging, but I can relate to the sense of accomplishment (and appreciate the little insight into the tech stack).
"The Moon has no oxygen atmosphere, so how can something explode? Lunar meteors don't require oxygen or combustion to make themselves visible. They hit the ground with so much kinetic energy that even a pebble can make a crater several feet wide. The flash of light comes not from combustion but rather from the thermal glow of molten rock and hot vapors at the impact site."
Combustion doesn't make things explode; it just heats things up so they vaporize. But there are other ways to heat things up, too, and the end result is the same.
I thought it was a weird footnote. I mean, do people really think that the rock would burn even if there was oxygen?
I suspect many meteors can and will combust. Lot's of things love oxygen bonds once they get enough energy and there is not a lot oxygen or heat in space.
(As you know Bob,) Explosions are kind of like rocket engines. They (generally) don't require external oxygen to happen. Quite a lot of explosions are solids (e.g. TNT) turning into a bunch of N2.
On the other hand, if something creates a bunch of gas in space, there's really no medium for a shock wave, other than the gas created. So it's not going to be as damaging. Though, there's no reason a sub-lunar explosion would be much different that what we get on the earth.
Back in 1982, I saw a very bright flash on the Moon - naked eye! It was early Sunday morning (5.22 am) on July 18th.
To this day, I'm not sure what caused it, and I've always eagerly followed up on any reports of 'transient Lunar phenomena', or, as in this instance, 'bright explosions'.
I once spoke to Patrick Moore about it, with a full description (I remember him asking if it was summer time - yes, it was). He was similarly intrigued, and promised to look into it, but I never managed to follow up...
People tend to focus on the size of projectiles from space, but
their great speed is often overlooked - from a simulator at:
http://impact.ese.ic.ac.uk/ImpactEffects/
>Impact Velocity - This is the velocity of the projectile before it enters the atmosphere. The minimum impact velocity on Earth is 11 km/s. Typical impact velocities are 17 km/s for asteroids and 51 km/s for comets. The maximum Earth impact velocity for objects orbiting the sun is 72 km/s
For comparison, the velocity of the ISS is about 7.7 km/s,
about equal to the speed of detonating cord.
The minimum impact velocity on Earth is 11km/s??? I beg to differ -- bodies can impact the Earth at arbitrarily low velocities. It depends on where they originate. There are clearly some assumptions being made there that aren't spelled out.
Starting from rest at a distance infinity, any object (regardless of it's own mass) necessarily undergoes a minimum increase in kinetic energy due to the gravitational potential of the mass of the target object (in this case the Earth, which has a known mass and so this is calculable). So I think the assumption is that the object isn't propelling itself away from the earth, and the object hasn't experienced any major competing gravitational forces inside the radius of the Moon's orbit.
Also, 11km/s isn't terribly quick on the celestial scale, I'd imagine.
>Impact Velocity - This is the velocity of the projectile before it enters the atmosphere. The minimum impact velocity on Earth is 11 km/s.
I think it's implied that the impacting objects come from outside the Earth-Moon System. Otherwise there would obviously be no minimum impact velocity.
No kidding. Shoot an 8-foot 2x4 at the Earth at 100km/sec and guess how fast the carbon-fluff will be going when it hits. The pieces of anything that breaks up as it descends will quickly slow to their terminal velocity at that height.
NASA says the February Russian fireball was going about 11.6 miles/sec when it blew up (14 miles up) but there's a lot of denser atmo in that 14 miles.
But without an atmosphere the shockwave from that 100 kiloton explosion should be pretty minimal (through the ground only), and any debris flung into the atmosphere would fall right back down on parabolic trajectories (or go into orbit), not linger in the sky for months/years.
The danger posed by such an explosion, off the top of my head, would be getting hit by the object itself, getting hit by falling debris ejected by the explosion, structural damage from the shockwave that traveled through the ground... I'm not sure what else.
Of course without an atmosphere everyone would be dead anyway, so I suppose this is kind of a silly thing to think about.
Sort of, there's still a blast wave from the vaporized rock, and there's still the ejecta blanket (which could easily ruin your day if any of it hit you).
How could it release more energy if it hits the ground? The total kinetic energy released must be the same whether it is released in the atmosphere or on impact with the ground.
100 kilotons of energy released along a several hundred kilometer long tube in the upper atmosphere, at altitudes of tens of kilometers poses much less of a threat to people who live on the surface of the Earth than if all that energy is released at once on the ground.
Define "damage", I guess. It's spread over a larger area, but there's a qualitative difference between widespread broken windows and a local 440 kiloton (per wikipedia) explosion on the ground that will level the surrounding terrain.
The primary cause of this discrepancy was engineering error.
Specifically, the flight system software on the Mars Climate
Orbiter was written to take thrust instructions using the
metric unit newtons (N), while the software on the ground that
generated those instructions used the Imperial measure
pound-force (lbf). This error has since been known as the
"metric mixup" and has been carefully avoided in all missions
since by NASA.
Can someone explain to me why this would be bright? I understand that this should send up a fair amount of ejecta but wouldn't most of the light be just from a reflection of the sun off of the particles?
If so, this isn't much of an explosion - it's just the most significant impact we've seen so far. I guess explosion is more interesting to the every-man.
The massive kinetic energy must be dissipated on impact. Some is consumed in displacing the material on the lunar surface. Some is converted into thermal energy, resulting in hot enough material to radiate energy in the visible spectrum.
Consider the absolutely insane energies involved - the report says "The 40 kg meteoroid measuring 0.3 to 0.4 meters wide hit the Moon traveling 56,000 mph."
That's a thing roughly half the size of a fridge. Traveling at a speed of about 25 kilometers, per second, coming to a full stop.
The ejecta aren't tossed about due to recoil they are lifted out of the ground by an expanding sphere of vaporized rock. And that vaporized rock glows because it is superheated to thousands of degrees, that's what creates the bright flash.
Do you have any reference for this? It seems like you're saying the vaporized rock is imparting force to the impacted surface, which is in turn ejected. I had not understood that the vaporized rock played a central role.
I thought the impactor imparted force directly to the surface. Basically there is a shock wave in the underlying rock which pushes ejecta out of a region underneath the impact site.
Let me backtrack a bit and say, more accurately that "the ejecta aren't just tossed about due to recoil", both effects play a role. My point was that the flash is caused by superheated/vaporized rock, which you will pretty much always get at such speeds due to the amount of energy released.
"Lunar meteor showers have turned out to be more common than anyone expected"
what does that mean? Is there more stuff flying through space than we thought? Does this have some consequence in the odds of hitting something in space?
It wasn't noticed live, the moon was recorded with the help of a telescope and the explosion was noticed later by an analyst.
I also doubt anyone could see that explosion without a telescope as the moon itself is quite bright.
The article says yes, but then quantifies it at 4th magnitude which really isn't that bright. Generally in my area you can't see anything 4th magnitude, nearly ever, due to light pollution. The thought of that right next to even a crescent moon sounds pretty hard to see even in dark skies.
I was going to say the same thing. While 4th magnitude is visible, it's not visible against the background of the already bright lunar surface. The Moon is very bright.
After some research online that night I began to doubt myself, most people concluded it was too rare and would not be visible.
The next day I saw someone asking in a newsgroup about the mysterious flash he had seen the night before while observing the moon through his telescope. Again, the general consensus was that he couldn't have seen an impact, it was too rare and would not be visible.
I checked with him and we both saw the flash at the same time.
I also saw a satellite transit the moon once with that same telescope, it was so cool.
And to think I don't even pull it out anymore. Sad....