Dear all -- I never interpreted any of your responses as an attack! I love lively debates and I am always grateful to lose false assumptions. Thank you for a stimulating and very educational discussion. -- Joe ------------------------------ On Sat, Aug 17, 2013 10:56 PM MDT Brent Watson wrote:
Joe,
All objects in the sky remain fixed in relation to the celestial sphere. They do not rotate from one part of the sky to another - they are fixed. That relationship does not change in relation to the celestial sphere. If one spiral arm points to the north celestial pole, or any other place on the celestial sphere, it will always point to that location. The same is true of one object in relation to another. It WILL NOT rotate. If you draw a great circle from one object to another you will see that the great circle does not move against the celestial sphere.
Now, specifically, the Perseid radiant, and NGC 6946 have a FIXED relationship with each other. The galaxy does not rotate against the celestial sphere. The path of a meteor against the celestial sphere is along a great circle. They cannot travel along a different path. If you do not believe this, please study your spherical trigonometry and physics. It can be no other way. Therefore, if you have two tracks across the galaxy, and they are not parallel nor coincident, they have to have different radiants. If they have different radiants then at least one of them is not a Perseid. It is simple geometry. Time has nothing to do with it. It is irrelevant because we are talking about objects on the celestial sphere.
What you are suggesting goes against all physics and geometry. At most, one of the traces in your images is a Perseid, and I question whether they are meteors at all.
Sorry to disagree, but "I cannot change the laws of physics" - nor geometry. Please do not interpret this as an attack against you personally. I am only questioning the assumption that you captured two Perseid meteors. I still like your images and find genuine interest in the color shift caused by the smoke. That is intriguing to me.
Brent
________________________________ From: Joe Bauman <josephmbauman@yahoo.com> To: utah-astronomy@mailman.xmission.com Sent: Saturday, August 17, 2013 2:00 PM Subject: Re: [Utah-astronomy] Galaxy NGC 6946 through smoke and meteriors
I wasn't claiming a Perseus could come from the North Star. I used that as a thought experiment to show that a meteor coming from a certain location will cross different constellations depending on when it happens because of the sky's rotaion. It works the same way with another meteor locus and a half-hour difference, just not as much of a difference. Celestial targets do rotate as you track them with a telescope but your tracking compensates for this. If you weren't automatically compensating you would need to use a clumsy device called a field derotator. Look up to see how it works. Just as the moon rotates from one pole up to the opposite pole up during the night, a galaxy does too. Pretend a galaxy is adjacent to the moon and you can see them both. Does the moon "stand on its head" while the galaxy doesn't? Now say the galaxy is in some other location and we're talking about half an hour. Do you imagine it has no rotational change in that period? If a meteor is coming through it a dust stream at 3:14 a.m. and another at 3:44, would the galaxy have rotated relative to the meteor source in that time? I think so bur I don't claim to know anything about celestial mechanics. -- Joe
------------------------------ On Sat, Aug 17, 2013 12:50 PM MDT Siegfried Jachmann wrote:
I think Brent is spot on.
On Sat, Aug 17, 2013 at 10:15 AM, Chuck Hards <chuck.hards@gmail.com> wrote:
Brent, I think Joe is just having trouble with polar coordinates. Joe, a straight line on the sky will always project as a curve on a 2-dimensional computer screen, unless extremely short. On Aug 17, 2013 9:23 AM, "Brent Watson" <brentjwatson@yahoo.com> wrote:
Joe,
I think we have to agree to disagree. A perseid can never come from the North Star. Likewise, north in your photo will always be north, and the direction the galaxy is facing relative to celestial north will not change. Your exercise of putting a piece of paper on your screen is not valid either. I am at a loss to be able to explain this unless we sit down together and use some visual aids, so lets agree to disagree.
Brent
________________________________ From: Joe Bauman <josephmbauman@yahoo.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Friday, August 16, 2013 11:38 PM Subject: Re: [Utah-astronomy] Galaxy NGC 6946 through smoke and meteriors
That's just not entirely true, Brent. The galaxy itself appears to rotate as the night progresses, even minute by minute, just as the moon ends upside down at sunrise from what it was at sunset. Let's remember first that the Perseids aren't really coming from Perseus but from a stream of dust through which Earth passes. The dust doesn't rotate as Earth does. Then do this thought experiment: pretend you're a meteor that's going to flash into our atmosphere from the direction of the North Star and cross the whole sky. If you do that in the middle of the night you cross a certain number of constellations that are up at that time. But if you decide to zoom in 12 hours later, during the day, you will cross an entirely different set of (unseen to Earthlings) constellations. The entry point was the same place and the angle of entry was the same but the trajectory crossed entirely different locations. If you vary that by an hour instead of half a day you still get a different track. A galaxy rotates as it crosses the sky just the way the moon does. I got my planetarium program going and I put the edge of a piece of paper from NGC6946 to Perseus. Then I advanced the time by half an hour. The galaxy rotated considerably in that time while I kept the paper pointed at Perseus. In half an hour the direction that the Perseid meteors streak across the galaxy changes. -- Joe
________________________________ From: Brent Watson <brentjwatson@yahoo.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Friday, August 16, 2013 9:31 PM Subject: Re: [Utah-astronomy] Galaxy NGC 6946 through smoke and meteriors
Joe,
The whole sky rotates at the same rate. It rotates very close to 1 hour of right ascension per hour of mean solar time, as measured by your watch. The angle between the radiant and the galaxy will not change, neglecting the movement of the radiant itself. (That movement happens over days, not minutes.) Both of those traces cannot be due to Perseid meteors because of the angle formed by the two traces. One of them MAY be, but the other is certainly not. How does the the line from the radiant intersect NGC 6946 as seen on your digital planetarium? Does it pass through at the same angle as one of the traces? If not, then both are either sporadic or not meteors at all.
Brent
________________________________ From: Joe Bauman <josephmbauman@yahoo.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Friday, August 16, 2013 6:09 PM Subject: Re: [Utah-astronomy] Galaxy NGC 6946 through smoke and meteriors
Looking at my computerized planetarium, it's certainly possible to draw a radiant from Perseus to NGC 6946 at the time I took the views, about 3:14 and 3:44 a.m., respectively, on Wednesday morning. I haven't had time to figure it out formally yet, but by running my planetarium program from the first to the second time it looks like NGC 6946 revolves about the same amount as the difference in the lines in the two subs. Because they are in different sections of the sky, the galaxy and the constellation revolve at different rates. So unless someone wants to be a lot more scientific about calculating these things and proves me wrong, I will continue to believe they are both Perseids. -- Joe
________________________________ From: Chuck Hards <chuck.hards@gmail.com> To: Utah Astronomy <utah-astronomy@mailman.xmission.com> Sent: Friday, August 16, 2013 4:40 PM Subject: Re: [Utah-astronomy] Galaxy NGC 6946 through smoke and meteriors
For the meteors to be considered Perseids, they must have radiated from the Perseid radiant. They can appear anywhere in the sky, and at any angle relative to the observer, but in order to be a member of a given shower, if you extend their path backwards across the sky, it must intersect the radiant. If it doesn't, it's a sporadic, or a member of a different shower. Some showers do overlap their times of activity.
All members of a given shower hit the earth's atmosphere at the same angle. They are traveling parallel in space. It just looks different to a ground-based observer.
Imagine the radiant as a sort of "vanishing point" in the sky.
On Fri, Aug 16, 2013 at 2:25 PM, Joe Bauman <josephmbauman@yahoo.com> wrote:
I did consult a star atlas ant I think they could be perseids -- meteorites seem to show up at various parts of the sky, not necessarily heading from Perseus directly. It is a wide stream of cometary dust
that
yge Earth passes through and I reckon that the atmosphere may hit the dust grains at various angles. Also saying the tracks look too uniform isn't a good way to judge them when you consider the field of view is tiny -- in a larger field they may have been less regular over s lmgrt stretch of their entry path. Well, that's my story and I'm stickin' with if! -- Thanks, Joe
------------------------------ On Fri, Aug 16, 2013 9:48 AM MDT Brent Watson wrote:
Joe,
They can't both be Perseids. They are coming from different directions. I am not sure where the Perseid radiant is with respect to your photograph, but in fact neither may be a Perseid. Please check the direction of travel. The tracks also look pretty uniform. In fact, almost too uniform to be meteors. Are they instead, satellites?
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-- Siegfried _______________________________________________ Utah-Astronomy mailing list http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy
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