5,296 reputation
1429
bio website keith-s-thompson.github.com
location San Diego, CA
age 55
visits member for 2 years, 11 months
seen Aug 25 at 22:20

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
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.
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
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.
Dec
8
comment Don't heavier objects actually fall faster because they exert their own gravity?
The classic experiment, as performed by Galileo and David Scott, involves dropping two objects simultaneously. In that case, the pull of the larger mass also affects the falling time of the smaller mass, as the Earth falls up and meets both objects slightly sooner. With <handwave>appropriate assumptions</handwave>, do they still hit simultaneously, or is there some tiny third-order effect I'm not allowing for?
Nov
23
comment Does Earth's Rotation Affect Its Shape?
@EMACK: I suggest updating your title to reflect exactly what you're asking. Your current title is ambiguous; you could be asking whether the Earth's rotation affects its shape, or how it does so, or why it does so.
Oct
30
comment Why does the moon look bigger at the horizon?
en.wikipedia.org/wiki/Moon_illusion
Oct
26
comment Dropping an object on the moon
And even if that weren't true (if the Moon were somehow stationary at the same distance from the Earth), the Moon's gravity would still be orders of magnitude stronger than the Earth's gravity.
Oct
20
comment Would two astronauts one in a satellite, one on top of a tower have the same experience?
Even if you're standing on the ground at sea level at the equator, your weight is slightly reduced by the rotation of the Earth. On a stationary tower at geosynchronous height, that effect would completely cancel out the force of gravity.
Oct
16
comment How does gravity work?
"How does gravity work?" "Fine, thanks!"
Oct
16
comment Could someone jump from the international space station and live?
@MathewFoscarini: I wasn't asking about the ISS vs. another orbiting object; I was asking about the ISS vs. a stationary platform. Of course no such platform currently exists.
Oct
16
comment Could someone jump from the international space station and live?
Is the question about jumping from the altitude of the ISS, about 400 km, starting at zero ground-relative velocity (say, jumping off a space elevator), or jumping from the ISS itself? The former gives you less velocity to kill, but also less atmosphere to use for braking; the latter gives you a shallow re-entry angle. I don't know which would be easier. Ignoring air resistance, a straight fall from 400 km would take about 5 minutes, with an impact speed of 2800 meters/sec -- much less that the station's orbital speed of 7700 meters/sec.
Oct
6
comment In a very small static universe with only a particle, does it make sense to talk about time?
Can the particle talk? 8-)}