I think the guidance about how deep you have to bury a moon base to be safe just got revised.
Cosmic rays? Nope - it's the meteors you really have to watch out for.
Bright Explosion on the Moon
41–50 of 66 posts
Re: Bright Explosion on the Moon
#42I 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 th…
You know what you must do now. Pull that sucker out and start looking at the skies again, with your kids too if you have them.
well, if he doesn't pull out - he will be grateful in a few months to have kids to share his discovery.
Re: Bright Explosion on the Moon
#43Can 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 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.
Best easy source: http://www.impact-structures.com/understanding-the-impact-cr...
Re: Bright Explosion on the Moon
#44Earlier quoted context omitted.
I wonder if the meteorite that exploded in the atmosphere over Russia did more or less damage than if it had struck the earth intact. Clearly Atmosphere makes a good shield for burning up the small meteorites - but I wonder if it exacerbates the damage from medium sized ones?
Had that impact hit the ground it would have released over 100 kilotons of energy. It would have been far, far more destructive and deadly.
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.
Re: Bright Explosion on the Moon
#45Earlier quoted context omitted.
Had that impact hit the ground it would have released over 100 kilotons of energy. It would have been far, far more destructive and deadly.
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.
The toal energy released is the same. The total energy released on the impact is quite different.
Re: Bright Explosion on the Moon
#46Earlier quoted context omitted.
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 fo…
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.
Re: Bright Explosion on the Moon
#47Re: Bright Explosion on the Moon
#48Can 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.
And this response, which is quite typical for laypeople like myself, shows why the site put that footnote on that article.
Apparently, the impact would be so hard that the rock heats up quite significantly.
Re: Bright Explosion on the Moon
#49Can 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.
Read rkaplan's comment above. In short, it's hitting with so much energy that the force of the impact alone is enough to leave the rock glowing-hot.
And even vaporize some of the material, thus an explosion.
Re: Bright Explosion on the Moon
#50Just 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
Why not replace the flash banner with an animated .gif?
Because the designer who insisted on the flash banner wanted to use flash. :P