Comments for privon.com | weblog http://privon.com/blog Traveling, Cycling, Climbing, Photography, and Astronomy. Fri, 26 Feb 2010 22:35:08 +0000 http://wordpress.org/?v=2.9.2 hourly 1 Comment on SDO Shockwave Redux – Enhanced Images & Analysis by George Privon http://privon.com/blog/photography/sdo-shockwave-redux-enhanced-images-analysis/comment-page-1/#comment-1290 George Privon Fri, 26 Feb 2010 22:35:08 +0000 http://privon.com/blog/?p=667#comment-1290 I'm not sure I completely understand your question, but acoustic waves are a type of pressure wave. If the rings in the image are in fact shockwaves from the rocket traveling faster than the speed of sound, it's a piling up of acoustic/pressure waves which results in the shockwave. As the rocket moves through the atmosphere, it pushes air out of the way, resulting in pressure waves. If the rocket is traveling faster than sound (as I likely the case here), it travels faster than the pressure waves, resulting in a <a href="http://en.wikipedia.org/wiki/Sonic_boom" rel="nofollow">sonic boom</a>. I suspect the sound you hear during a rocket launch is dominated by the combustion of fuel and flow of exhaust out of the engines, not pressure waves off the rocket itself. Also, the rocket didn't become supersonic until around a minute or more after liftoff, so you wouldn't have heard a sonic boom before then. <i>"Also, the SDO launch seemed to take off very slow when compared to other launches. Did that play a part in the ability to actually see these phenomena? Why did it seem to take off so much more slowly than other launches? Was that part of the plan? Did SDO need a slower launch speed? Just asking…"</i> Actually, the Atlas V that launched SDO apparently had a "hot" engine and went a little bit faster than normal. The reason it left the pad so slowly (compare to shuttle launches for example) is the lack of booster rockets for this particular launch. So it takes the rocket a bit longer to get up to speed. With the appropriate cloud conditions, this might be visible for other launches, even those with boosters and more acceleration. <i>"...would the waves reappear again or have they been there all along and we just haven’t seen them or noticed them until now. </i> This aspect is a bit unclear. That has been a suggestion that if these are shockwaves from super- or trans-sonic travel, they should be there all the time. If that is the case, they might still not always be visible as you probably need specific atmospheric/cloud conditions to actually see the shockwaves. There's some more discussion on the details is on the APOD discussion board: <a href="http://bb.nightskylive.net/asterisk/viewtopic.php?f=9&t=18448" rel="nofollow">Exceptional Rocket Waves Destroy Sun Dog Discussion</a>. I’m not sure I completely understand your question, but acoustic waves are a type of pressure wave. If the rings in the image are in fact shockwaves from the rocket traveling faster than the speed of sound, it’s a piling up of acoustic/pressure waves which results in the shockwave. As the rocket moves through the atmosphere, it pushes air out of the way, resulting in pressure waves. If the rocket is traveling faster than sound (as I likely the case here), it travels faster than the pressure waves, resulting in a sonic boom.

I suspect the sound you hear during a rocket launch is dominated by the combustion of fuel and flow of exhaust out of the engines, not pressure waves off the rocket itself. Also, the rocket didn’t become supersonic until around a minute or more after liftoff, so you wouldn’t have heard a sonic boom before then.

“Also, the SDO launch seemed to take off very slow when compared to other launches. Did that play a part in the ability to actually see these phenomena? Why did it seem to take off so much more slowly than other launches? Was that part of the plan? Did SDO need a slower launch speed? Just asking…”

Actually, the Atlas V that launched SDO apparently had a “hot” engine and went a little bit faster than normal. The reason it left the pad so slowly (compare to shuttle launches for example) is the lack of booster rockets for this particular launch. So it takes the rocket a bit longer to get up to speed. With the appropriate cloud conditions, this might be visible for other launches, even those with boosters and more acceleration.

“…would the waves reappear again or have they been there all along and we just haven’t seen them or noticed them until now.

This aspect is a bit unclear. That has been a suggestion that if these are shockwaves from super- or trans-sonic travel, they should be there all the time. If that is the case, they might still not always be visible as you probably need specific atmospheric/cloud conditions to actually see the shockwaves.

There’s some more discussion on the details is on the APOD discussion board: Exceptional Rocket Waves Destroy Sun Dog Discussion.

]]> Comment on SDO Shockwave Redux – Enhanced Images & Analysis by PinkyLeft http://privon.com/blog/photography/sdo-shockwave-redux-enhanced-images-analysis/comment-page-1/#comment-1289 PinkyLeft Fri, 26 Feb 2010 21:08:09 +0000 http://privon.com/blog/?p=667#comment-1289 Someone at ACW said that the rings/waves appeared at the same time. Why wouldn't they be acoustic rather than pressure waves from the force of the rocket? If they do appear at the 'same time', it would have to be a rather fast force moving through the atmosphere that would play off the layers as it passes through. Wouldn't sound be that fast and direct? Since the noise from your average launch isn't a steady one tone noise, wouldn't it make sense to say that it was the harmonics in the sounds of the launch that caused the waves? That would explain the flattening at the top as the rocket was approaching the speed of sound. Right? Possibly? I'm probably wrong, but have waves like this been seen in other launches? Also, the SDO launch seemed to take off very slow when compared to other launches. Did that play a part in the ability to actually see these phenomena? Why did it seem to take off so much more slowly than other launches? Was that part of the plan? Did SDO need a slower launch speed? Just asking... If another Atlas were launched at that speed, or slower, would the waves reappear again or have they been there all along and we just haven't seen them or noticed them until now. If they are pressure waves then this opens a different chapter into the interrelations of things on this planet, does it not? Someone at ACW said that the rings/waves appeared at the same time. Why wouldn’t they be acoustic rather than pressure waves from the force of the rocket? If they do appear at the ’same time’, it would have to be a rather fast force moving through the atmosphere that would play off the layers as it passes through. Wouldn’t sound be that fast and direct? Since the noise from your average launch isn’t a steady one tone noise, wouldn’t it make sense to say that it was the harmonics in the sounds of the launch that caused the waves? That would explain the flattening at the top as the rocket was approaching the speed of sound. Right? Possibly? I’m probably wrong, but have waves like this been seen in other launches? Also, the SDO launch seemed to take off very slow when compared to other launches. Did that play a part in the ability to actually see these phenomena? Why did it seem to take off so much more slowly than other launches? Was that part of the plan? Did SDO need a slower launch speed? Just asking…

If another Atlas were launched at that speed, or slower, would the waves reappear again or have they been there all along and we just haven’t seen them or noticed them until now. If they are pressure waves then this opens a different chapter into the interrelations of things on this planet, does it not?

]]> Comment on Star Trails and Meterology(?) by George http://privon.com/blog/photography/star-trails-and-meterology/comment-page-1/#comment-1249 George Wed, 02 Dec 2009 23:45:35 +0000 http://privon.com/blog/?p=591#comment-1249 Yea, it was really bright, enough to cast shadows. I have another (longer!) picture of the telescope which looks even more like day. I'll show it to you when I get back to Cville. Yea, it was really bright, enough to cast shadows. I have another (longer!) picture of the telescope which looks even more like day. I’ll show it to you when I get back to Cville.

]]> Comment on Star Trails and Meterology(?) by Nicole http://privon.com/blog/photography/star-trails-and-meterology/comment-page-1/#comment-1248 Nicole Wed, 02 Dec 2009 22:50:03 +0000 http://privon.com/blog/?p=591#comment-1248 OOOh pretties. They do look like daylight with that long full moon exposure. OOOh pretties. They do look like daylight with that long full moon exposure.

]]> Comment on Paper Writing in Astronomy by George http://privon.com/blog/astronomy/paper-writing-in-astronomy/comment-page-1/#comment-1245 George Sun, 22 Nov 2009 16:51:43 +0000 http://privon.com/blog/?p=555#comment-1245 I'm not sure which statistical methods in particular you're referring to, so I can't say if those in particular are being used, but there is a fair amount of statistics use in astronomy. Sometimes correcting for completeness, statistics using data with upper/lower limits, etc. And statistical methods will probably become more prevalent as we get larger data sets from the big surveys that are coming online. I’m not sure which statistical methods in particular you’re referring to, so I can’t say if those in particular are being used, but there is a fair amount of statistics use in astronomy. Sometimes correcting for completeness, statistics using data with upper/lower limits, etc. And statistical methods will probably become more prevalent as we get larger data sets from the big surveys that are coming online.

]]> Comment on Paper Writing in Astronomy by Justin http://privon.com/blog/astronomy/paper-writing-in-astronomy/comment-page-1/#comment-1244 Justin Sun, 22 Nov 2009 16:42:01 +0000 http://privon.com/blog/?p=555#comment-1244 Ah. I was just wondering if science actually uses this stuff or not. I guess not, oh well. I will be a part of the consulting center for TAMU in a couple of years so I guess I'll just have to be patient and wait to see what this Stats stuff can really do, other than determine cause from time to death for rats... Plus the distance thing was a thought experiment - I'm just trying to wrap my head around why someone would use this stuff. Also, beware Chi-Squared for continuous data - it will always have higher Type II error than more advanced tests. Perhaps another test will be more appropriate especially for low sample size, but then again 6-7 objects is REALLY low and letting the computer run for hours and hours to obtain your p-value from a modern test may not be any more informative. Well, good luck! Anyway, good to chat with you! Let me know if you are travelling home over Christmas break so we can get together. My number is on Facebook. TTYL, -J Ah. I was just wondering if science actually uses this stuff or not. I guess not, oh well. I will be a part of the consulting center for TAMU in a couple of years so I guess I’ll just have to be patient and wait to see what this Stats stuff can really do, other than determine cause from time to death for rats… Plus the distance thing was a thought experiment – I’m just trying to wrap my head around why someone would use this stuff. Also, beware Chi-Squared for continuous data – it will always have higher Type II error than more advanced tests. Perhaps another test will be more appropriate especially for low sample size, but then again 6-7 objects is REALLY low and letting the computer run for hours and hours to obtain your p-value from a modern test may not be any more informative. Well, good luck! Anyway, good to chat with you! Let me know if you are travelling home over Christmas break so we can get together. My number is on Facebook. TTYL, -J

]]> Comment on Paper Writing in Astronomy by George http://privon.com/blog/astronomy/paper-writing-in-astronomy/comment-page-1/#comment-1240 George Mon, 16 Nov 2009 03:28:33 +0000 http://privon.com/blog/?p=555#comment-1240 Until recently, astronomy has suffered from small number statistics. With the large surveys that are happening now, people are actually able to get large enough samples of objects to do real statistics. With the data I'm writing up, the analysis mostly consists of measurements off the images. I have images of radio galaxies and you can see some areas where hydrogen gas has absorbed background radio waves. So I measure the optical depth of the absorption. There won't be much use of statistics in this paper because the sample is so small (6-7 objects). The closest we've come is correlating estimates of the amount of intervening gas from radio (absorption) and X-ray absorption measurements. Another project I'm working on is fitting models to data. I've been using the Levenberg-Marquardt chi-squared minimization to determine the best model fit. Naturally, it's somewhat difficult to interpret when you have a model with 15 free parameters! But, that project is for a single galaxy, so other than minimizing chi-squared, there isn't any statistical study per se (except maybe exploring the uncertainties in the "best fit" parameters). As far as the galaxy distance, we know that already from redshift measurements in optical spectra (basically using the doppler effect and Hubble's Law). But, having said that, I need to brush up on statistics... Until recently, astronomy has suffered from small number statistics. With the large surveys that are happening now, people are actually able to get large enough samples of objects to do real statistics.

With the data I’m writing up, the analysis mostly consists of measurements off the images. I have images of radio galaxies and you can see some areas where hydrogen gas has absorbed background radio waves. So I measure the optical depth of the absorption. There won’t be much use of statistics in this paper because the sample is so small (6-7 objects). The closest we’ve come is correlating estimates of the amount of intervening gas from radio (absorption) and X-ray absorption measurements.

Another project I’m working on is fitting models to data. I’ve been using the Levenberg-Marquardt chi-squared minimization to determine the best model fit. Naturally, it’s somewhat difficult to interpret when you have a model with 15 free parameters! But, that project is for a single galaxy, so other than minimizing chi-squared, there isn’t any statistical study per se (except maybe exploring the uncertainties in the “best fit” parameters).

As far as the galaxy distance, we know that already from redshift measurements in optical spectra (basically using the doppler effect and Hubble’s Law).

But, having said that, I need to brush up on statistics…

]]> Comment on Paper Writing in Astronomy by Justin http://privon.com/blog/astronomy/paper-writing-in-astronomy/comment-page-1/#comment-1239 Justin Sat, 14 Nov 2009 05:46:44 +0000 http://privon.com/blog/?p=555#comment-1239 So what kind of analysis do you do? Surely Statistical in some frame or another. I'm curious (mostly since we only look at studies right now and not work with real data) as to how you analyze your data. Do you use current theory in Astronomy and then sift your data for parameter estimates for those models? Like finding distance from us to your objects. I'm sure the radio gives some sort of time increment that you would then run a statistical method on to get an estimate of a typical value from which you can determine some distance. I may be way off track, but I'm trying to see where data analysis fits in real scientific work - I'm the worst ever at methods. It seems like that's all I do in a class built around handling various data, and let me tell you it is soo interesting... ;) So what kind of analysis do you do? Surely Statistical in some frame or another. I’m curious (mostly since we only look at studies right now and not work with real data) as to how you analyze your data. Do you use current theory in Astronomy and then sift your data for parameter estimates for those models? Like finding distance from us to your objects. I’m sure the radio gives some sort of time increment that you would then run a statistical method on to get an estimate of a typical value from which you can determine some distance. I may be way off track, but I’m trying to see where data analysis fits in real scientific work – I’m the worst ever at methods. It seems like that’s all I do in a class built around handling various data, and let me tell you it is soo interesting… ;)

]]> Comment on Public AGN Talk Tomorrow! by David Miller http://privon.com/blog/astronomy/public-agn-talk-tomorrow/comment-page-1/#comment-1220 David Miller Tue, 01 Sep 2009 23:56:25 +0000 http://privon.com/blog/?p=498#comment-1220 Looking forward to hearing your talk! Dave Miller CAS member Looking forward to hearing your talk!

Dave Miller
CAS member

]]> Comment on Ireland Day 2: Powerscourt & Glendalough by Nicole http://privon.com/blog/hiking/ireland-day-2-powerscourt-glendalough/comment-page-1/#comment-1104 Nicole Tue, 02 Jun 2009 22:10:57 +0000 http://privon.com/blog/?p=393#comment-1104 Wow, I am soooo jealous! Those pictures are gorgeous. Wow, I am soooo jealous! Those pictures are gorgeous.

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