Starship Asterisk*

Animation: Perseid Meteor Shower

Explanation: Where do Perseid meteors come from? Mostly small bits of stony grit, Perseid meteoroids were once expelled from Comet Swift-Tuttle and continue to follow this comet's orbit as they slowly disperse. The featured animation depicts the entire meteoroid stream as it orbits our Sun. When the Earth nears this stream, as it does every year, the Perseid Meteor Shower occurs. Highlighted as bright in the animation, comet debris this size is usually so dim it is practically undetectable. Only a small fraction of this debris will enter the Earth's atmosphere, heat up and disintegrate brightly. Tonight and the next few nights promise some of the better skies to view the Perseid shower as well as other active showers because the first quarter moon will be absent from the sky from midnight onward.

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This animation is wrong. The Perseids must cross the ecliptic close to the Earth in a direction opposite to the motions of the planets. Their speed relative to Earth is about 60 km/s, but in the animation it would only be about 20 km/s. In other words, their orbit is retrograde, not prograde.

I've got nothing to say about astronomy or this APOD other than to remark how impressive doing this animation in a web page is to me. I suppose it's all done with JavaScript that the browser is running? My limited page analysis tools show this:

Uli Bastian wrote: ↑Sun Aug 11, 2024 7:00 am This animation is wrong. The Perseids must cross the ecliptic close to the Earth in a direction opposite to the motions of the planets. Their speed relative to Earth is about 60 km/s, but in the animation it would only be about 20 km/s. In other words, their orbit is retrograde, not prograde.

Their orbit is retrograde. It's just a little hard to see since their orbital plane is nearly perpendicular to Earth's. Tilt the viewing angle and look closely.

johnnydeep wrote: ↑Sun Aug 11, 2024 1:08 pm I've got nothing to say about astronomy or this APOD other than to remark how impressive doing this animation in a web page is to me.

Agreed, it's brilliant. Now if only it included a date indicator...

[And, dang. Them bots is gettin' smart.]

raschumacher wrote: ↑Sun Aug 11, 2024 3:55 pm [And, dang. Them bots is gettin' smart.]

"Bots"? What bots? (I ain't no dang bot!)

Concerning the fact that the animated orbit INDEED is retrograde:
Thanks, I got the point. It is, indeed. Very nice. In order to avoid my misunderstanding with other people, it might be considered to change the start-up viewing perspective of the animation. If you make the start-up view perpendicular to the ecliptic (i.e. with the Earth orbit appearing as a near-perfect circle), the meteoroid cloud looks equally nice, and the retrograde orbit - as well as the velocity of the meteoroids wrt the Earth - become unambiguous.

Uli Bastian wrote: ↑Mon Aug 12, 2024 1:44 pm Concerning the fact that the animated orbit INDEED is retrograde:
Thanks, I got the point. It is, indeed. Very nice. In order to avoid my misunderstanding with other people, it might be considered to change the start-up viewing perspective of the animation. If you make the start-up view perpendicular to the ecliptic (i.e. with the Earth orbit appearing as a near-perfect circle), the meteoroid cloud looks equally nice, and the retrograde orbit - as well as the velocity of the meteoroids wrt the Earth - become unambiguous.

Yes, the default viewing orientation creates the illusion that the orbital plane of the debris lies on the ecliptic. Another useful trick is to color the particles according to whether they are above or below the ecliptic.

johnnydeep wrote: ↑Sun Aug 11, 2024 5:39 pm "Bots"? What bots? (I ain't no dang bot!)

That's just what a bot *would* say! :_>

(I meant, of course, the bots which the "Submit" puzzles are designed to foil, and not your most hu-man admirable self.)

raschumacher wrote: ↑Mon Aug 12, 2024 3:27 pm

johnnydeep wrote: ↑Sun Aug 11, 2024 5:39 pm "Bots"? What bots? (I ain't no dang bot!)

That's just what a bot *would* say! :_>

(I meant, of course, the bots which the "Submit" puzzles are designed to foil, and not your most hu-man admirable self.)

Hmm. "Submit puzzles"? You mean that you are presented with a puzzle to solve correctly when using the "Submit" button to submit a post here? If so, I never see that... perhaps because I've created an assount?