Re: [Utah-astronomy] WHITE FLAG -- was Galaxy NGC 6946 through smoke and meteriors
Well, rats. ------------------------------ On Sat, Aug 17, 2013 7:48 PM MDT Jared Smith wrote:
:-) It's all good. This was actually a really good thought experiment. I had to really think through it and draw things out myself (and even then I wasn't absolutely sure).
As I examine the angle at which the objects passed through the galaxy (assuming the orientation of NGC6946 in Stellarium is correct - which it usually is), both were at almost 90 degree angles to Perseus. This would make it quite unlikely for them to be Perseids. For what it's worth, I think it most likely that they are satellites, but we'll never know for sure.
Jared
On Sat, Aug 17, 2013 at 7:18 PM, Joe Bauman <josephmbauman@yahoo.com> wrote:
OK OK I admit I was wrong. But I think one of my two streaked subexposures may have been a Perseid. Maybe this debate was only because of my directional dydlexia. -- Joe
------------------------------ On Sat, Aug 17, 2013 7:09 PM MDT Jared Smith wrote:
Sorry Joe, but this photo proves that you're incorrect. It shows a bunch of Perseids and one non-Perseid. Because the Perseids all originate from the same point, no matter what time of night a photo is taken, a Perseid will always pass through the same point of sky at the same angle.
http://i.imgur.com/lVyDxEF.jpg
Above is an illustration showing the radiant from Perseus to Andromeda Galaxy (green line) and also from Polaris to Andromeda Galaxy (red line) at both late night and early morning. No matter the time, the Perseid will pass through Andromeda following the same path relative to true north (55.8ยบ angle between the two lines in both examples). If you follow a straight line from point A to point B you can only intersect point B at exactly one angle relative to point B.
Jared
On Sat, Aug 17, 2013 at 5:28 PM, Joe Bauman <josephmbauman@yahoo.com> wrote:
OK, I would like to know what you non-roadblacks think of this. It clearly shows Perseid mterors traveling in different vectors. Look especially at the one aimed at the top of the mountain and the one right below it. Draw their trajectories back a short distance and they would actually cross. If someone were taking a several-minutes exposure of the galaxy and got a photo of both trails, Chuck would claim they weren't Perseids. What you fail to understand is that the dust forms a broad river above the atmosphere and the dust grains can intersect the river at many points and enter the atmosphere in many directions. To quote you, if you can't accept this simple fact or believe this photo, there's just no sense in arguing. -- Joe
http://www.google.com/imgres?imgurl=http://i.space.com/images/i/000/020/498/...
------------------------------ On Sat, Aug 17, 2013 4:14 PM MDT Chuck Hards wrote:
You are battling a conceptual roadblock, Joe. The radiant does rotate with the stars as the earth turns. You need to bone-up on meteor showers and the way a radiant works as seen from the ground.
This discussion is pointless until then. On Aug 17, 2013 4:02 PM, "Joe Bauman" <josephmbauman@yahoo.com> wrote:
No, the radiant does change because it comes from an essentially unmoving stream of dust particles in space generally toward the northeast. As Earn rotates relative yo this stream different sections of the atmosphere impact it. The stream is a physical trail that the Earth bumps against as Earth turns.
------------------------------ On Sat, Aug 17, 2013 3:46 PM MDT Chuck Hards wrote:
What you are forgetting, Joe, is that the radiant is rotating with the sky as well. The relationship between the target galaxy and the radiant doesn't change. On Aug 17, 2013 3:19 PM, "Joe Bauman" <josephmbauman@yahoo.com> wrote:
Field rotation is relative to the observer on Earth -- true. But the tracking telescope compensates for it, meaning that the view in the camera actually rotates as the camera does. A shot fired across the view from the northeast part of the sky -- the trail of a Perseid metetor -- will cut across the frame at one direction. When the camera has rotated for half an hour a shot from the same northeastern section would seem to cross the frame at a different angle. The stream of dust is still coming from the northeast but the galaxy has rotated a certain amount relative to it. The distance of the target from the North Star will dictate how much difference there is. -- Joe
------------------------------ On Sat, Aug 17, 2013 2:33 PM MDT Chuck Hards wrote:
But they do not rotate relative to the RA/DEC coordinate grid, which is the crux of this discussion. Field rotation, which is rotation relative to an observer on earth, has nothing to do with it. You keep invoking it Joe, and It's really outside the matter of determining if a meteor is a Perseid or not.
Brent is correct. On Aug 17, 2013 2:23 PM, "Joe Bauman" <josephmbauman@yahoo.com> wrote:
Right, but celectial objects do rotate relative to that line. -- Joe
------------------------------ On Sat, Aug 17, 2013 10:15 AM MDT Chuck Hards 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? > > > _______________________________________________ Utah-Astronomy mailing list http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy
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Joe Bauman