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Himanshu Raj
2007-Jan-09, 03:10 PM
Why we see more meteors from midnight to dawn than from evening to midnight?

:think: One explanation that I am trying to reason out is that when a particular portion of the Earth (the place from where we are viewing) is changing its position from the evening time to the morning time it moves away from the sun. The dust trails left by the comet's entry are continously pushed radially away form the sun dew to the pressure of the solar wind. So the relative velocity of the dust and earth's atmosphere decreases so that frictional force that results form the drag force of the earth's atmosphere, decreases (as drag force is directly proportional to velocity squared). At mid-night that part of the earth is at its farthest position and now starts to move towards the sun. This resuts in the increment of the relative velocity between the earth's atmosphere and the dust particles. Therefore friction increases and the debris burn faster and at a higher rate. so we see more meteors from midnight to dawn than from evening to midnight.

Another mild reason could be that the pollution levels, dew to the dust particles in the earth's atmosphere, is less in the morning than during the dusk.

Few other questions that i am curious to know are:

1. Why might some stars appear double in blue light through they could not be resolved in red light?

2. Altair (a Aquila) has a parallax of p = 0".198, proper motion m = 0".658/year. What does this statement mean?

3. The 12 Zodiacal signs are equally extended on the ecliptic. In which of them does the Sun lie in for the shortest period?

Himanshu

01101001
2007-Jan-09, 03:35 PM
Why we see more meteors from midnight to dawn than from evening to midnight?

For the same reason there's more dead bugs on your car's windshield (windscreen) than on the side windows or back windows.

Now imagine your car moved more slowly down the road, and didn't always travel nose first, but skidded down the road, spinning wildly -- like the earth rotates as it revolves around the Sun. The bugs would hit all different places, but you'd expect them at any particular time mostly to hit on the side of the car that currently happens to face forward.

That's the midnight-to-noon side of Earth. And the meteors are most easily seen when it's dark: midnight to dawn.

This web page has a nice diagram that says it better: Meteors, Meteoroids and Meteorites (http://cseligman.com/text/meteors/meteors.htm)

I'll let someone else try your other questions. If no one does, I expect you'd get more action by separating them out, and using the board's Questions and Answers (http://www.bautforum.com/forumdisplay.php?f=8) Forum.

Tog
2007-Jan-09, 03:36 PM
Why we see more meteors from midnight to dawn than from evening to midnight?
Most meteors are little bits of dust that are already there when the Earth moves into them. It's sort of the same reason you get more bugs on the front of your car than the back when you drive. From midnight on, you on the "front" of the Earth.

Few other questions that i am curious to know are:

1. Why might some stars appear double in blue light through they could not be resolved in red light? No clue on that one.

2. Altair (a Aquila) has a parallax of p = 0".198, proper motion m = 0".658/year. What does this statement mean?
Parallax is how far something seems to move when you look at it from two different points. If you had a spider on a window and covered one eye you could measure the angle between the spider and a mountain in the back ground. If you closed the other eye and did it again, you could get the Parallax of the spider which is just a way to say how far it looks like it moved from one eye to the next. For stars, we use two different points on the Earth's orbit and compare the angle to the stars in the background. If we know how far apart our two places are when we did the measurements, we can get a pretty good idea of how far away the object is.

Proper motion is when the spider walks across the window. It's a measure of the speed. Since the sky is measured in degrees, proper motion is measured in degrees minutes and seconds per year. Nothing really seems to move very fast though.

3. The 12 Zodiacal signs are equally extended on the ecliptic. In which of them does the Sun lie in for the shortest period?
Himanshu
If they are equally spaced then the Sun spends an equal amount of time in each :D. For astrology, I think they assume that each sign covers 1/12 of the sky, or 30 degrees. In reality, the Sun passes through at least 13 constellations, spending only a few days in either Libra or Scorpius. I can't recall which.

I hope this helps. Welcome to the forum.

gwiz
2007-Jan-09, 03:41 PM
1. Why might some stars appear double in blue light through they could not be resolved in red light?
A telescope focusses a star to a small dot, the diffraction disc, the size of which depends of the wavelength of the light. Blue light has a shorter wavelength than red and hence produces a smaller diffraction disc. This can mean that a double star appears as two separate discs rather than two overlapping ones.