Comet PanSTARRS and the Helix Nebula.
Copyright: Sebastian Voltmer.
I was actually surprised to see today's APOD image of Comet PanSTARRS, because lately there have been many fine images of this comet passing by the Helix Nebula posted in the Recent Submissions forum. I think Sebastian Voltmer's picture at left is particularly lovely.
But I certainly don't complain about seeing today's Helix-less APOD! I always love the chance to compare the colors of stars with the colors of comets. The bright-looking fourth magnitude blue star in today's APOD, Iota Pi
scis Austrini, is intrinsically a bit brighter than Vega (59 times solar versus 48 for Vega) and a little bit bluer. In today's APOD, Iota PsA is just as
blue as the coma of the comet is
green. Actually the
HEX designation I used to make that greenish color corresponds to OIII emission at 500.7 nm. But in the picture of Comet PanSTARRS and the Helix Nebula at left, the inner, OIII-dominated part of the Helix Nebula is clearly bluer than the green coma of the comet. All the other PanSTARRS/Helix images in the
Recent Submissions forum also show the inner part of the nebula to be bluer than the coma of the comet. The color of the coma must be due to the emission of specific green wavelengths by the comet, most of them longer than the 500.7 nm wavelength of the OIII emission of so many planetary nebulas, among them the Helix.
Interesting! And thanks to everyone who has contributed photogenic images of Comet PanSTARRS here recently.
Ann
[float=left][img2]https://c2.staticflickr.com/8/7637/27187674570_79b5b05f06_b.jpg[/img2][c][size=75]Comet PanSTARRS and the Helix Nebula.
Copyright: Sebastian Voltmer.[/size][/c][/float] I was actually surprised to see today's APOD image of Comet PanSTARRS, because lately there have been many fine images of this comet passing by the Helix Nebula posted in the Recent Submissions forum. I think Sebastian Voltmer's picture at left is particularly lovely.
But I certainly don't complain about seeing today's Helix-less APOD! I always love the chance to compare the colors of stars with the colors of comets. The bright-looking fourth magnitude blue star in today's APOD, Iota Pi[i][b]s[/b][/i]cis Austrini, is intrinsically a bit brighter than Vega (59 times solar versus 48 for Vega) and a little bit bluer. In today's APOD, Iota PsA is just as [b][color=#0080FF]blue[/color][/b] as the coma of the comet is [b][color=#00ff92]green[/color][/b]. Actually the [url=https://academo.org/demos/wavelength-to-colour-relationship/]HEX designation[/url] I used to make that greenish color corresponds to OIII emission at 500.7 nm. But in the picture of Comet PanSTARRS and the Helix Nebula at left, the inner, OIII-dominated part of the Helix Nebula is clearly bluer than the green coma of the comet. All the other PanSTARRS/Helix images in the [url=http://asterisk.apod.com/viewtopic.php?p=258513#p258513]Recent Submissions[/url] forum also show the inner part of the nebula to be bluer than the coma of the comet. The color of the coma must be due to the emission of specific green wavelengths by the comet, most of them longer than the 500.7 nm wavelength of the OIII emission of so many planetary nebulas, among them the Helix.
Interesting! And thanks to everyone who has contributed photogenic images of Comet PanSTARRS here recently.
Ann