5,286 reputation
1530
bio website keith-s-thompson.github.com
location San Diego, CA
age 55
visits member for 3 years
seen Oct 8 at 18:08

I'm a programmer and all-around nerd living in San Diego, California.
I work at JetHead Development Inc.

E-mail: Keith.S.Thompson@gmail.com


Feb
26
comment Density of stars near the center of the Milky Way
@theJollySin: Not really. I've updated my answer with a link to a Wikipedia article that gives different figures.
Feb
26
revised Density of stars near the center of the Milky Way
Link is dead, add another
Feb
17
comment Stresses in asteroid during close flyby
Tide is the difference in (gravitational) acceleration over distance. It falls off with the cube of the distance from the primary, which is why the Moon's tidal effect on the Earth is stronger than the Sun's. For an asteroid near Earth, the (differential) force from the tide and the asteroid's own gravitational cohesion are both fairly small; within Roche's limit, the tide exceed's the asteroid's gravity. The net gravitational force on the asteroid is zero, since it's in free fall, so I don't think "jerk" comes into it, except perhaps as a second or third order effect.
Feb
16
revised Stresses in asteroid during close flyby
added 60 characters in body
Feb
16
answered Stresses in asteroid during close flyby
Feb
15
comment Is the moon a planet?
If we discovered, say, a Neptune-sized body in a nearly circular orbit at 150 AUs, I think we should call it a "planet". And we've detected hundreds of "planets" orbiting other stars. If we're going to use the word, I think we should have a consistent definition for it.
Feb
12
awarded  Good Answer
Jan
28
comment Is it possible for a physical object to have a irrational length?
Every object's length is rational if you use its own length as the unit of measurement. 8-)}
Jan
28
comment Planet's Moon attrated by sun
The behavior in the video certainly looks wrong (the gray dot is the Moon, right?) -- but the Moon does pretty much orbit the Sun. From an Earth-centered frame of reference, the Moon is in a basically elliptical orbit around the Earth. From a Sun-centered frame of reference, the Moon's path around the Sun is distorted by the Earth's gravity, but the path is still convex.
Jan
16
comment The theory of moon creation when a Mars size planet hit Earth
@zadane: No, that's not how it works. Drag doesn't just slow the satellite's motion by x; it slows it continuously over time. Gravitational force pulls a satellite towards the body it's orbiting, and for a stable elliptical or circular orbit it just curves the satellite's path. Drag always acts opposite to the direction of motion, slowing the satellite down and changing its orbit.
Jan
14
comment How far are constellations recognizable?
Proxima Centauri isn't visible to the naked eye; its apparent magnitude is 11.05. It's only barely visible from Alpha Centauri (magnitude about 4.8 if I've done the math correctly). (Higher magnitude numbers are dimmer; the limit of naked-eye visibility is around 6, or 6.5 if you have really good eyes.)
Jan
3
comment Could much of the “missing” antimatter make up neutrons?
The neutron is not its own antiparticle. The antineutron is a distinct particle. It happens to have the same charge as the neutron (zero), but it has other characteristics that distinguish it.
Dec
26
comment What is Energy made of?
Energy isn't made of other things; other things are made of energy.
Dec
22
revised Do the stars imaged by a telescope even exist at present?
added 160 characters in body
Dec
21
revised Do the stars imaged by a telescope even exist at present?
Discuss Milky Way supernova frequency
Dec
19
awarded  Nice Answer
Dec
19
comment Can I survive a free fall using a ramp and a rope?
A little elasticity in the rope might be enough to fling the ramp ahead of you. Not that the while idea is particularly realistic.
Dec
19
comment Can I survive a free fall using a ramp and a rope?
The question states that the ramp is very light. The idea is that when you reach the end of the rope, the ramp is pulled up along with you without significantly slowing you down. It then lands on the ground ahead of you, ready to cushion your fall again. (The ramp, of course, is made of pure unobtainium.)
Dec
9
comment How might clock synchronization work with RSA SecurID tokens?
Sounds like you could mess up the server's idea of your token's clock drift by waiting a while before entering your code, or entering one you generated a few minutes ago. I don't think that's exploitable, though.
Dec
8
comment Is there a small enough planet or asteroid you can orbit by jumping?
Another approach: Take a rock with you, and throw it directly backwards when you're half way around. This should give you enough extra velocity so your orbit doesn't intersect the surface at your starting point.