Comment on what you estimate is your measurement accuracy. How many significant figures are meaningful? (In other words, can you measure the diameter to an accuracy of one pixel? One tenth of a pixel? One hundredth of a pixel? None of these?)
How much fainter in DN units is the sunspot than its surroundings?
Repeat your measurement of the Sun’s diameter several times and post your average value of the diameter in kilometers on the Blog. Include a comment about sig figs.
Describe the general nature of the sun's surface around the location of this sunspot.
Assignment 2
ReplyDeleteAnalyzing the sun’s image using jimage software
My min/max was 2258/5518.
The brightest spot was at 5052
The precision of the data does not mean that it is accurate. There is much more error in trying to decide where the edge of the sun is and trying to estimate whether the line drawn is a diameter. The accuracy must be greater than 1 pixel.
I found that the sunspot was at 2959 DN
The surrounding were at 4263 DN.
So the sunspot was about 1300 DN fainter.
My average diameter was 1404094km with a standard deviation of 6182km. The standard deviation is a measure of the accuracy. The precision is 0.01 km but there are much sources of measurement error. I would say we should only quote the data to 3 sig figs. So the average value I have measured is 1400000km
Nature of sun’s surface around sun spot. I found this part confusing. My image seemed to blurred to give any description about the surface except there was a bright C shaped object to the left of the sun spot.
I am anxious to do this one, but where is the image of the sun located? How to I find it?
ReplyDeleteGo to the web site
ReplyDeleteFinding the sun image
go to azastro.pbworks.com
go to module 1
half way down there is a link to the file solar_image.fits
Click on it and it will download
Good Luck
Barry
Sorry I need to rewrite my comment
ReplyDeleteTo find the sun image
Go to web page
azastro.pbworks.com
go to module 1
halfway down there is a link to the file solar_image.fits
Click on it and it will download.
Good luck
Barry
I found the sun, not sure how I didn’t know about the website, but now I do, I’m ready to rock-n-roll!
ReplyDeleteThe Min/Max for contrast/brightness was 2247 – 5259 and I was able to find a DN value of 5463.
The sunspot had a DN of 2655 at its lowest and the surrounding area had a DN of 5070, for a difference of 2415 DN.
My estimate for the diameter of the sun is 952 pixels, accuracy was not even close, I would say that the value could be off by as many as 5-8 pixels. It was hard to find a true edge, even more difficult to estimate a true diameter, range of values was between 948 and 958. This translates to Average diameter of 1391405 km with a standard deviation of 3989 km.
Following Barry’s argument about sig figs, I would agree that this is likely only accurate to 2 or 3 sig figs to limit my measurement to 1390000 km for the diameter of the Sun.
Around the sun spot I notice a bright region giving way to lines radiating outwards. There also seems to be some sort of flare (or bright spot) emanating from it.
I like playing with new software – I even discovered that the shift key works in conjunction with the mouse to give straight lines (much like Microsoft programs allow).
The largest DN value I found was 5463 located at x = 738 and y = 780.
ReplyDeleteHow accurate was my length measurement? To investigate this, I zoomed into the limb of the sun until I could really see the individual pixels. I then tried to measure the length of one pixel, and the smallest length I could get the tool to measure was 0.06 pixels. I also noticed that when zoomed in, there isn’t a clear edge to the sun. The pixels get dimmer and eventually have a DN value of zero. So is the edge of the sun when the DN value drops to zero or is it when the DN value starts to drop, or somewhere in between. This brings in a possible error of 4-5 pixels of picking the start point for your measurement and then another possible 4-5 pixel error in deciding where to end your measurement. So even though the computer can measure to a precision of 0.06 pixels, there is much more error in deciding where the edge of the sun is, so I conclude that my accuracy is within 10 pixels.
Moving on to measuring the brightness of the sunspot. I found it to have a value of 2694 and the neighboring continuum to have a value of 4775 making the sunspot half as bright as the neighboring area. I also noticed that right next to the sunspot was a brighter region than the surrounding continuum, measuring in at a value of 5128, but decided it would make more sense to compare the sunspot brightness to the general area, instead of to a unique “hot spot”.
My value for the sun’s diameter is 13,950,947 km, which differs from the “known” diameter by around 40,730 km. However, since my measurement error was 10 pixels, that translates to an error of 144,898 km. So while my precision isn’t as good as the scientists with a 52 km error bar, at least I’m in the ball park. I guess this means I have to give my sun’s diameter as 13,900,000 ±144,898 km. I’m confused as to wether my error of ±144,898 km has that many sig figs.
Finally, on to the general nature of the Sun’s surface. I can see the granulation effect on the sun, the alternating bright and dark regions. There also seems to be a brighter ring around the sunspot when compared to the surrounding region. What causes this effect? Also, I noticed a bright region to the left of the sunspot in the shape of a large C.
I really enjoyed using ImageJ and look forward to using it with my students next year.
Assignment 2
ReplyDeleteThe largest DN value I got is 5559. I set up the scale to just one pixel. The meaningful number of significant figures should be 3 significant since my measurement is just an approximation. It depends on the line you draw in the imageJ.
From imageJ, my average diameter is 13911369.225 km and my approximate diameter is 13900000 km.
The sunspot has a 2655 DN value and it is 50% fainter than its surrounding.
A sunspot is a region on the Sun's photosphere that is cooler and darker than the surrounding area
The DN value I found was 5,300. I'm thinking that the DN is actually the value on the gray scale. Is the gray scale just a measurement of how light or dark something is?
ReplyDeleteI compared my values for diameter of the sun in pixels and noticed that the values only vary in the ones place (+/- 3). Therefore, I'm thinking that my measurements are accurate to 10 pixels. This means that I have 3 significant figures. I am certain about the first 2 and uncertain about the last one; it is estimated.
The sunspot is about 1000DN units fainter than its surroundings.
The average value of the Sun's diameter is 13900102 km. I erased all of my measurements, and needed to solve this by using the pixel to km conversion that was given on the set scale screen (way cool!). I had written down the "area" values and tried to solve for the diameter of the sun this way, but that didn't work. I'm not sure why.
Again, I looked at all of my values and noticed that they had the same value for the first three values, so, diameter is accurate to 1X106.
Close up, the sun looks like a bowl of soup hot, brothy soup, or, concentrated acid mixing with water. I could see something that looked like a flare nearby the sunspot.
I would really like to know about that mysterious CCD processing number (the one that is 32768 larger than the DN) . I'm really unsure as to what a pixel is. My current understanding is that it is a region on a detector in which photons are converted into electrons. Are pixels uniform sizes between detectors? If they aren't, how can we have a conversion factor to km?
Using B & C min and max of 0 & 4740 (I notice my values are different than my classmates - confused how we are doing it so differently!), respectively, the brightest spot I found was at x=740,y=784 with a value of 5414.
ReplyDeleteI found the next part of the assignment I found difficult since I'm working on my tiny tablet computer screen without a mouse...but the average measurement I came up with was a width of 960 pixels, +/- 4 pixels. SO despite the extra digits shown on the screen, I realistically have 3 significant figures only.
Looking at the sunspot at (788, 788) I measured its brightness as 2719, with the area to the right averaging about 4300 and two spikes to the left that maxed at 5100.
Measuring the size of the image did average out to about 1390000 km, with uncertainty of +/- 4000 (about the same as with measuring pixels, not too surprisingly!)
On the magnified image, the dark center of the spot is surrounded by an area of slightly less dark, but around that is an area that appears brighter than the surroundings
I tried to analyze the solar image using the imageJ, the brightest DN value that I found is 5581, the x coordinate is 739 and y coordinate is 780. The sunspot has a DN value of 2655, its x = 777 and y =789. I measured the diameter of the sun ten times and my estimate for the diameter is 1094 pixels. The average diameter that I got in kilometer is 1392020, the measurement I used is only up to 1 pixel. It is likely that the accuracy of the measurement is up to 3 significant figures to limit my measurement to 1390000.
ReplyDeleteThe sunspot is the darker and cooler part of the sun, its DN value is approximately 50% fainter compared to its surrounding.
I got DN=5559 (740,780) for the white spot and DN=2655 (777,789) for the dark spot. The dark spot has a lesser value for DN and 50% fainter (with a difference of 2904 DN units). I can say that sunspot is a darker and cooler area of the sun photosphere.
ReplyDeleteMy measurement for the diameter is 1393936.727 (using imageJ). Since my measurement were definitely approximations. My measurement is not accurate to +/- 10 pixels or 1000 km. The measurement of the diameter should be in the point of the circle and it should divide the circle into two equal parts. Since we are dealing with approximations, the diameter of the sun must be reported to 3SF and my diameter is 1390000 km.
This software is very cool!
ReplyDeleteThe largest DM value I found within my adjusted image of the sun was 5478.00. Measuring the diameter, I got 920.009 pixels. When I tried to make the shortest possible line that I could on the image, it was two pixels long. I think that means that my measurement is reliable to the tenths place, so 920 would be valid. When plotting the profile of the sunspot, I found that the actual spot is 2600 DN units fainter than its surroundings (highest value on graph was 5100, lowest was 2500). After setting the scale to reflect the actual diameter of the sun and measuring several times, I got an average length of 1375989. Since this scale is based on pixel length, which I said before could probably only be measured to two significant figures, the km length can only be measured to two significant figures: 1400000 km. After magnifying the sunspot, I saw that there is a very bright flare to the left of the spot. The light is a bit brighter than average directly surrounding the spot. Also, there seems to be a pattern of lines going into the spot, as if stuff is getting sucked in.
The highest DN value that I found was 5581 at x= 739 y=780 and it was found in the white spot of the sun’s surface.
ReplyDeleteThe minimum DN in the sunspot is 2655. It is almost half of the DN of the brightest part of the sun’s surface.
The approximate measurement of the sun’s diameter is 13,900,000 km. I did some manipulation of the scale and I found out that the measurement accuracy should be up to one pixel. The precision of the measurement depends on the accuracy of setting up the two points of the circle for the diameter. My average measurement I obtained using imageJ is 13914062.602 km. My average diameter is written up to 3 SF (13,900,000 km). This is the most précise measurement I could have using imageJ.
The sunspot is the dark area of the sun’s surface. Its surface temperature is lower than the surrounding area.
From John Webster
ReplyDeleteAfter adjusting the Brightness and Contrast I got a Min Reading of 2969 and a Maximum of 5529. The largest DN value I got was 5472.
I repeated the measurements 4 times and got an average of 965 pixels. This produced an average measurement of 1393445.474 Km for the diameter. The variations come from my initial Min/Max adjustment trying to approximate where the outermost circumference of the Sun appears. This adjustment is done without knowledge of the pixel length.
The DN reading I got for 778, 788 was 2801 which is about 1500-2000 DN fainter than its surroundings.
Upon magnification, the Sun in that area seemed like a bubbly surface. Next to the spot was a bright swirl to the upper left. There was also a darker arc about 225° relative to the spot.
Step 2: The largest value I found was a DN value of 5572 at x = 739 and y = 781.
ReplyDeleteStep 3: Measurement accuracy: My first value I recorded gave me three places after the decimal. The other values didn't have any places after the decimal. After I closed the window and started over, those values had the three decimal places (don't know why they disappeared in some of my measurements).
I can see from others' measurements that we all “do it differently”. When I measured the diameter, I measured it from top to bottom and tried to keep the x value the same. I figured then I was measuring in the same place but if I didn't pick the right place, then the average of my values will be farther off than if I eye-balled it differently each time.
I think my measurement varied by 1% so since my average was 966, I would say one could measure to an accuracy of 9-10 pixels.
Step 4: This estimate can vary greatly depending on if one takes the average of the numbers or the highest and lowest numbers. I chose to use average and got that the sunspot is 1700 DN units fainter than its surroundings.
Step 5: I got an average diameter of 1,389,000 km. I chose to use as many sig figs as in the actual diameter number given to us. I see two times that error can creep in: the first is that we enter in our average pixel length which is an estimate so that now becomes the “yard stick” by which we measure our calculated diameter which we are estimating again! I think, however, that it would be very important for the same person to do both sets of measurements since I would think that we would tend to measure similarly each time and by the numbers others are getting, I see that we all “do it differently”.
Step 6: I really liked magnifying the sunspot. After I did so, I adjusted the brightness & contrast again. I think it looks really cool colored red. For some reason it made it easier to imagine that the surface of the sun isn't smooth like a polished marble. Although I know that the differences in color actually refer to temperature differences, it made me think more of a change in topography.
My measurements of the sun's diameter is approximately 1392789.754 km(1091 pixel). I did 30 trials. I also try to manipulate the distance from 3 decimal places up to a whole number and rounding off to the nearest tens. I believe my measurement cannot be accurate up to +/- 10 pixels or 100 km.
ReplyDeleteSince everything is just an approximation my measurement should be reported to 3significant figure (1390000 km). The precission of my measurement depends on the ability to get the actual points of the circle so what I did is to zoom in the image and try to put my point on the edge of the image. I used a ruler to divide my circle into two equal semicircles.
The sunspot is darker in appearance and has a cooler temperature than its surrounding. The highest DN I have in the surface of the sun is 5559 and the lowest DN is 2655. It's almost 2900 units fainter than its surrounding.
Nice job, all! Let me address a question Bekkah asked several posts above:
ReplyDelete"I'm really unsure as to what a pixel is. My current understanding is that it is a region on a detector in which photons are converted into electrons. Are pixels uniform sizes between detectors? If they aren't, how can we have a conversion factor to km? "
You have the right idea: each pixel is like a bucket that collects photons (light) while the shuter is open and converts them to electronic charge. When the camera shutter closes the chip is "read out" (see the CCD tutorial we posted) and the charge in volts is converted to a number (expressed in binary form, so typically something like 2^16 possible values are possible. Pixels are all the same size on any chip. This number is an important parameter, and that allows us, for example, to convers to km in this exercise. (But often in astronomy we have a very poor estimate of how big something is! BTW, I have a great demo of how a CCD works, and reads out: it involves a low box filled with paper cups, and skittles (M&Ms work too...)
why are we getting different values for DN?
ReplyDeleteAssignment 2
ReplyDeleteThe brightest pixels on the sun appear to be at around 4893. If I set the minimum value near this maximum value I can see that they are associated with splotchy regions spread across the surface of the sun.
More observations, I can see from the histrogram that there are essentially two different parts to the image. The pixels from brightness 648 to 972 appear to represent an outer annulus surrounding the sun. It is unclear to me if this extended feature is part of the sun or some kind of artifact of the image analysis. The middle part of the sun is mainly within the brightness scale of 2677 to 4690.
I took 4 measurements of length, obtaining 942.002, 956.075, 934.009, and 939.106 pixels. This gives me a mean of 942.798. Since the measurements are precise to about the tenth spot I would say that a reasonable value would be 940 plus or minus 15.
When I look at the histogram of the cross section of the sun the lowest the grey value slips is about 3750, as compared to a maximum of 4700 or so.
After several measurements the average diameter of the sun appears to be approximately 30,000,000. It is unclear to me why I am getting an answer that is so far off the correct answer, I think there must be something incorrect about how I am using the progam, but I am unsure what it might be.
When I zoom in to examine the sunspot pixilation is quite apparent. The total size of the sunspot (in pixels) appears to be about 14 pixels across and 16 pixels high. The sunspot gets successively darker as you look from the outside to the inside and the inner four pixels are about all equally dark.