Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: [Phys-l] Figuring Physics in the March TPT The Physics Teacher

Sorry...Bad Astronomy is a blog written by Phil Plait, and it routinely has the latest "hot" (or "cool") astronomy news. Sometimes the Planetary Society Blog will have "it" first, but BA is a good site for astronomy tidbits and pictures. Sometimes he gets onto other issues which can quickly degenerate in the comments.

Any object in a picture you take has a sharpness (or fuzziness) that depends on the angular size of the object and the resolving power of the camera (or telescope in this instance). Angular size in radians is roughly object diameter divided by distance from observer to object. Multiply by 57.3 to get degrees. Multiply again by 60 to get arc-minutes. Multiply by 60 again to get arc-seconds. The Hubble picture (which looked really "sharp") was of an object that was 1.5 arc-minutes in perspective size. A full moon viewed from Earth is about 30 arc-minutes. The new pic on the BA blog site is 13/1000 of an arc-SECOND. There is no way that Hubble could even touch that. The pic is of a dying star that has swollen to a size that, if it were our Sun, would engulf the Earth; it has then thrown off a layer of material. The pic show the gap between the layer and the star. Impressive picture of a star BEGINNING to die. Phil has the details of the telescopes, and the technique, used to make the picture.

Enjoy!

Brian Whatcott <betwys1@sbcglobal.net> 2/19/2009 7:20 pm >>>
Bill Nettles wrote:
.....
Bad Astronomy had a good picture of a planetary nebula that was 2 AU across at a distance of 500 LY. It was kind of fuzzy, not nearly as pretty as some Hubble pictures of other planetary nebula, but they were 4.3 LY across at 10000 LY distance. but when you compare the angular sizes, the quality of the first becomes dramatically impressive (13 milliarcseconds versus 1.5 arc-minutes).
I read this passage twice, and it means as much to me now as before I
read a word.
So this is how decrepitude begins? :-)

Brian W


_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l