Explanation: Arcing toward a fiery fate, this Sungrazer comet was recorded by the SOHO spacecraft's Large Angle Spectrometric COronagraph(LASCO) on December 23, 1996. LASCO uses an occulting disk, partially visible at the lower right, to block out the otherwise overwhelming solar disk allowing it to image the inner 8 million kilometers of the relatively faint corona. The comet is seen as its coma enters the bright equatorial solar wind region (oriented vertically). Positioned in space to continuously observe the Sun, SOHO has now been used to discover over 1,500 comets, including numerous sungrazers. Based on their orbits, the vast majority of sungrazers are believed to belong to the Kreutz family of sungrazing comets created by successive break ups from a single large parent comet that passed very near the Sun in the twelfth century. The Great Comet of 1965, Ikeya-Seki, was also a member of the Kreutz family, coming within about 650,000 kilometers of the Sun's surface. Passing so close to the Sun, Sungrazers are subjected to destructive tidal forces along with intense solar heat. This small comet, known as the Christmas Comet SOHO 6, did not survive. Later this year, Comet ISON, potentially the brightest sungrazer in recorded history but not a Kreutz sungrazer, is expected to survive.
The image presented on the APOD page is cropped slightly on one side and rotated 90 degrees CW, compared with the full image you get when you click on the image on the APOD page. It makes the caption descriptors "lower right" and "oriented vertically" difficult to follow.
And how is the "occulting disk" at the "lower right"? What then, is the big bloody circle in the middle of the image?
Are you sure this APOD is not the artwork from a David Bowie album from the 1970s?
Re: APOD: Sungrazer (2013 Oct 27)
Posted: Sun Oct 27, 2013 11:48 am
by Morty
***
And how is the "occulting disk" at the "lower right"?
***
I had the same question. Noodling around, I found this photo in the link http://en.wikipedia.org/wiki/Kreutz_Sungrazers the caption's author provided. Apparently that was the image he was referring to when he wrote that description.
Morty
Re: APOD: Sungrazer (2013 Oct 27)
Posted: Sun Oct 27, 2013 1:13 pm
by owlice
I've let the APOD editor know; thanks for your comments.
Re: APOD: Sungrazer (2013 Oct 27)
Posted: Sun Oct 27, 2013 1:16 pm
by Cousin Ricky
Are those diffraction rings around the occulting disc? I never noticed those before.
Cousin Ricky wrote:
Are those diffraction rings around the occulting disc?
I never noticed those before.
http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/bardif.html#c1 wrote:
<<An Euler spiral or Cornu spiral describes diffraction from the edge of a half-plane. The beam of a laboratory helium-neon laser was spread with a telescope eyepiece and directed at a machined metal edge. The diffraction pattern was photographed on a screen approximately four meters from the edge. Barrier diffraction must be handled by the techniques of Fresnel diffraction. One way to approach the calculation is by use of the Cornu spiral.>>
<<An Euler spiral or Cornu spiral is a curve whose curvature [k = 1/r] changes linearly with its curve length. Euler spirals are also commonly referred to as spiros or clothoids.
Euler spirals have applications to diffraction computations. They are also widely used as transition curve in railroad engineering/highway engineering for connecting and transiting the geometry between a tangent and a circular curve.
An object traveling on a circular path experiences a centripetal acceleration. When a vehicle traveling on a straight path suddenly transitions to a tangential circular path, it experiences a sudden centripetal acceleration starting at the tangent point; and this centripetal force acts instantly causing much discomfort (causing jerk).
On early railroads this instant application of lateral force was not an issue since low speeds and wide-radius curves were employed (lateral forces on the passengers and the lateral sway was small and tolerable). As speeds of rail vehicles increased over the years, it became obvious that an easement is necessary so that the centripetal acceleration increases linearly with the traveled distance. Given the expression of centripetal acceleration V² / R, the obvious solution is to provide an easement curve whose curvature, 1 / R, increases linearly with the traveled distance. This geometry is an Euler spiral. Marie Alfred Cornu (and later some civil engineers) also solved the calculus of Euler spiral independently. Euler spirals are now widely used in rail and highway engineering for providing a transition or an easement between a tangent and a horizontal circular curve.>>
Re: APOD: Sungrazer (2013 Oct 27)
Posted: Sun Oct 27, 2013 4:17 pm
by Ann
Nitpicker wrote:
Are you sure this APOD is not the artwork from a David Bowie album from the 1970s?
Of course, Chris Hadley was very good too, wasn't he?
Click to play embedded YouTube video.
Ann
Re: APOD: Sungrazer (2013 Oct 27)
Posted: Sun Oct 27, 2013 6:40 pm
by Canadian Grandma
I would like to thank all those participants whose comments over the last couple of years have helped me to slightly better understand things astronomical; and today would like especially to thank Ann for posting the clips about Chris Hadfield-which I had not had the chnce to see before.
Joyce
Re: APOD: Sungrazer (2013 Oct 27)
Posted: Sun Oct 27, 2013 10:29 pm
by Nitpicker
Thanks to everyone above for their helpful (and polite) responses to my outburst. Whilst Ann tends to favour the blue end of the spectrum, it appears I have problems at the (bloody) red end.
dblow.PNG (174.92 KiB) Viewed 2857 times
Good album by the way. Not sure I understand all of it, but I love it.
And RIP Lou Reed. Vale.
Re: APOD: Sungrazer (2013 Oct 27)
Posted: Sun Oct 27, 2013 10:56 pm
by bay area john
As shown on the APOD, the photo looks to me like a Starfleet logo/poster for a Star Trek movie.
Re: APOD: Sungrazer (2013 Oct 27)
Posted: Mon Oct 28, 2013 3:18 am
by BillBixby
So happy to see a picture posted from the historic past which I know I had not seen previously as it was prior to my discovery of APOD. Much information to be learned, still. Thank you to the 10 (9 live) 'posters' who have commented on this this historic pic. A search of the historic past shows this pic is from the per-historic DISCUSS (some days disgust) days of the APOD archives.
If you have withheld commenting on today's pic due to previous discussion, please comment. There is no per-history.
Always interested in your thoughts on the APOD pic,
Bill
Re: APOD: Sungrazer (2013 Oct 27)
Posted: Mon Oct 28, 2013 5:34 pm
by Ann
BillBixby wrote:So happy to see a picture posted from the historic past which I know I had not seen previously as it was prior to my discovery of APOD. Much information to be learned, still. Thank you to the 10 (9 live) 'posters' who have commented on this this historic pic. A search of the historic past shows this pic is from the per-historic DISCUSS (some days disgust) days of the APOD archives.
If you have withheld commenting on today's pic due to previous discussion, please comment. There is no per-history.
Always interested in your thoughts on the APOD pic,
Bill
I'd love to say something intelligent here, but comets, alas, are not my forte. The best I can say is that comets grow long tails as they approach the Sun, because ices in them evaporate. (As if you didn't know that already.)
The closer they come to the Sun, the more of their ices evaporate, and the brighter they are likely to get. But quite a few comets meet their maker(?) as they plunge into the Sun. This is a nice Youtube video showing the demise of such a hapless comet. Perhaps even more interesting is the Sun's reaction to being fed this snack.
Click to play embedded YouTube video.
Ann
Re: APOD: Sungrazer (2013 Oct 27)
Posted: Mon Oct 28, 2013 5:53 pm
by geckzilla
Ann wrote: Perhaps even more interesting is the Sun's reaction to being fed this snack.
Click to play embedded YouTube video.
Ann
A complete coincidence, of course. A small comet has no means of having any major effect on a star like the Sun.
Re: APOD: Sungrazer (2013 Oct 27)
Posted: Mon Oct 28, 2013 6:01 pm
by Chris Peterson
geckzilla wrote:A complete coincidence, of course. A small comet has no means of having any major effect on a star like the Sun.
That is almost certainly the case, although there is a very slight statistical suggestion (based on a small sample size) to the contrary. Probably just noise, however.
In the case of this video, however, we can certainly say there is no cause-effect phenomenon, since the comet is only getting to the edge of the occulting disc when the CME occurs, nowhere near the Sun itself (which is indicated by the white ring inscribed on the occulting disc).
Re: APOD: Sungrazer (2013 Oct 27)
Posted: Mon Oct 28, 2013 8:03 pm
by Beyond
Yeah, it seems that the comet completely disappears before it gets there, just before an amazing coincidence happens with the sun, that at first gives the impression that the comet was evaporated to smithereens in a big POOF! Except that the POOF! is just toooo big to have been gotten from such a small comet.
Sungrazer
