Why are there more meteors after midnight?

[lukebl]

As I sit here waiting for some Perseids I’ve been giving some thought regarding the frequency of meteors before midnight and after midnight. i.e. the fact that meteors are apparently more frequent after midnight than before. 

The perceived wisdom is that in the morning the earth is rotating INTO the meteoroid, and thus the relative speed is greater, air friction is greater, and the meteors are brighter and otherwise faint ones are more visible. In the evening the earth is rotating AWAY from the meteoroid, so the relative speed is slower, ipso facto less air resistance, less friction and the meteors are fewer and less bright.

HOWEVER, my understanding is that meteors are travelling at, say, 30,000 mph or more, while at the equator the earth is rotating at around 1000 mph (and effectively zero at the poles). So the speed of the Earth’s rotation is pretty negligible compared to the meteor’s speed, and can’t really have a significant effect on the meteor’s entry speed? A meteor hitting the earth’s atmosphere at 31,000 mph surely can’t be significantly brighter than one hitting it at 29,000 mph?

Or am I just being stupid? 
 

[globular]

Isn’t it just that there are more hours of darkness after midnight than before… especially in the summer due to daylight saving.  Or have I misunderstood your point?

[lukebl]

17 minutes ago, globular said:

Isn’t it just that there are more hours of darkness after midnight than before… 

Well, that what I think too. But as I said, various guides (books, internet, magazines, etc) perpetuate the claim that there are more meteors in the hours before dawn because the earth is rotating into them.

I’ve never bought that unfounded claim for the reasons I said in my post.

[globular]

If they tend to be travelling inwards towards the sun (and I imagine that being attracted to the sun is likely to dominate in this region of space) then it would seem logical that The Earth would get in the way on the side facing away from the sun more often than not… i.e. the bit in darkness at the time…

Im just guessing / speculating… and I”m sure you”d rather get a response from someone who knows… so sorry about that.

Edited August 11, 2021 by globular

[Tiny Clanger]

A previous thread has some good explanations (and some confusing ones too)

 

[lukebl]

8 hours ago, Tiny Clanger said:

A previous thread has some good explanations (and some confusing ones too)

Thanks. I missed that earlier thread. 

I found this quote from National Geographic: “Think of it like an automobile that has a windshield on the side facing forward,” Murphy says. “You get more bugs on the front windshield than you do on the back window.”

Like I said. I don’t buy it! The difference in relative speed of the meteor before and after midnight would be insignificant. The bugs are still flying into the back window nearly as fast as on the front windshield.

[wxsatuser]

It is excepted amongst us radio amateurs that the best time for random meteors is from midnight to about midday.

When I did meteorscatter I always tried to get skeds after midnight but you had to be quick to get in before the best slots were taken.

I have no idea if the speed matters but we definitely got more meteors in the hours just before and after sunrise.

[Tiny Clanger]

1 hour ago, lukebl said:

Thanks. I missed that earlier thread. 

I found this quote from National Geographic: “Think of it like an automobile that has a windshield on the side facing forward,” Murphy says. “You get more bugs on the front windshield than you do on the back window.”

Like I said. I don’t buy it! The difference in relative speed of the meteor before and after midnight would be insignificant. The bugs are still flying into the back window nearly as fast as on the front windshield.

Is it perhaps more a matter of angle of incidence than relative speed ?

Rather than bugs on the windscreen, I was thinking of using the analogy of walking into heavy rain in a high wind : walk straight into the wind direction and your face gets hit by more drops and the rain seems subjectively stronger. That makes sense to me, but may not be a good analogy at all !

Heather

[randomic]

Could it be a doppler effect? When the surface of the Earth is moving towards the source of the meteors the observed frequency will be higher, and then lower when moving away.

I can't imagine it would account for more than a 5% frequency difference though.

 

Edit: Hang on, just occurred to me that the rotation is probably completely irrelevant:

Isn't it just that from midnight-midday you're on the side of the earth which is going "forward" into the meteors? And from midday-midnight you're going "backwards"? The bugs on the windshield analogy seems spot on.

Edited August 12, 2021 by randomic

[scotty1]

I think as the earth rotates during the night, earth faces headon into the meteor stream in the early hours. 

With the Perseids the radiant is higher after midnight too. 

I didn't see any last night too murky. Six on Tuesday night, also last Friday one Perseid seen

[lukebl]

1 hour ago, randomic said:

sn't it just that from midnight-midday you're on the side of the earth which is going "forward" into the meteors?

But, like I said, if the meteors are travelling at 30,000mph and the earth is rotating at 1000 mph, it wouldn’t make much difference whether the earth was rotating into the storm or away from it. i.e. the speed of the meteor entering the atmosphere would be c. 29,000mph in the evening and 31,000mph in the morning. Not much difference. 

[randomic]

39 minutes ago, lukebl said:

But, like I said, if the meteors are travelling at 30,000mph and the earth is rotating at 1000 mph, it wouldn’t make much difference whether the earth was rotating into the storm or away from it. i.e. the speed of the meteor entering the atmosphere would be c. 29,000mph in the evening and 31,000mph in the morning. Not much difference. 

You misunderstand me. I mean not the Earth's rotation but it's motion in orbit around the Sun. Which is more like 70,000 mph!

Meteors are not so much being fired at the Earth from a particular direction and are more debris in the path of the Earth's orbit with which it collides.

Remember this is also not about the speed at which the meteors hit the atmosphere but the frequency.

During midday to midnight, the same number of meteors are hitting Earth, it's just that most of them are hitting the other side of the planet from you.

[lukebl]

8 minutes ago, randomic said:

During midday to midnight, the same number of meteors are hitting Earth, it's just that most of them are hitting the other side of the planet from you.

Fair enough! I think I get now. Many thanks!

[vlaiv]

12 minutes ago, randomic said:

During midday to midnight, the same number of meteors are hitting Earth, it's just that most of them are hitting the other side of the planet from you.

I was just thinking of that as an explanation.

After midnight - several things come together. Position of radiant and hence part of the sky that you'll be able to see and darkness and level of LP - all that comes together after midnight until the morning when sunshine spoils everything.

[wulfrun]

After local midnight you're on the hemisphere at the "front" of the Earth (from the point of view of direction of orbital travel). Before that you're on the "trailing" side, which is shielded by the Earth itself from anything that can't overtake its orbital speed. Clearly there's a gradual rather than an abrupt shift but that's my understanding of the mechanism. "Bugs-on-the-front-windscreen" kind of effect.

EDIT: clearly this only applies to cometary (or other) debris-fields, other random junk can overtake the "trailing" hemisphere any time, given sufficient speed.

Edited August 12, 2021 by wulfrun
as per

[pete_l]

14 hours ago, lukebl said:

But as I said, various guides (books, internet, magazines, etc) perpetuate the claim

Books and articles are full of things that just copy ideas from other books and articles. History books in particular are infamous for perpetuating stuff that has no factual basis. So it would not surprise me if someone simply thought this was true, ages ago, and since then every other writer has just copied it.

However, it seems to me that this cannot be true. Since it is always before midnight in as many places as it is after midnight at the same time!

[vlaiv]

1 minute ago, pete_l said:

However, it seems to me that this cannot be true. Since it is always before midnight in as many places as it is after midnight at the same time!

Not sure if this is applicable - it's like saying that Sun can be seen in midnight - because it can be seen by someone as our midnight is their noon. They can see it, but we can't

Similarly, Sun will be at highest position when it is noon in our local time, so will incidence of detected meteors be highest when it is midnight (or past midnight) at our local time. There will be 6pm somewhere else - and at that place - they won't see their highest incidence at that moment - but later at their midnight.

[wxsatuser]

Have a look at this

https://skyandtelescope.org/astronomy-blogs/explore-night-bob-king/random-meteors-arent-random02112015/