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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