5,392 reputation
1631
bio website keith-s-thompson.github.com
location San Diego, CA
age 55
visits member for 3 years, 2 months
seen 13 hours ago

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


Mar
30
comment Is Feynman's explanation of how the moon stays in orbit wrong?
@MarkMitchison: Good point, I've updated my answer accordingly.
Mar
30
revised Is Feynman's explanation of how the moon stays in orbit wrong?
added 48 characters in body
Mar
30
answered Is Feynman's explanation of how the moon stays in orbit wrong?
Mar
18
revised How does space affect the human body (no space suit, no space craft)
Link to YouTube video
Feb
27
comment What's the surface area of a liquid? How does evaporation increase if the surface area of a liquid is increased?
If you have a tall glass of water with a given fixed surface area, it will lose a constant amount of water per unit of time (in an identical environment); the deeper the water, the longer it will last. But for a given volume, the large the surface area that's exposed to air, the more quickly it will evaporate.
Feb
26
comment What's the surface area of a liquid? How does evaporation increase if the surface area of a liquid is increased?
Why would having more surface molecules make the evaporation rate decrease?
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