APOD: Comet PANSTARRS and the Andromeda Galaxy (2013 Apr 03)

[APOD Robot]

Comet PANSTARRS and the Andromeda Galaxy

Explanation: Currently, comet PANSTARRS is passing nearly in front of the galaxy Andromeda. Coincidentally, both comet and galaxy appear now to be just about the same angular size. In physical size, even though Comet PANSTARRS is currently the largest object in the Solar System with a tail spanning about 15 times the diameter of the Sun, it is still about 70 billion times smaller than the Andromeda galaxy (M31). The above image was taken a few days ago near Syktyvkar, Russia. As C/2011 L4 (PANSTARRS) on the lower left recedes from the Sun and dims, it is returning to the northerly direction whence it came. When the comet will return is currently unknown, although humans may have merged with computers by then.

<< Previous APOD

This Day in APOD

Next APOD >>

[/b]

[saturno2]

Comet Panstarrs and the Andromeda Galaxy, two different astronomical
objects, but here they have a interesting unit of image

[Ann]

Thanks for commenting on this image, saturno2! I agree, it's a nice image. It is always fun when two "cosmic objects" that are wildly different in size appears to be similar, because of their vastly different distances from us. I suppose that if we know how big these two objects are intrinsically, then we can figure out how much farther away Andromeda is than PANSTARRS!

As always, I find the colors of the objects interesting. Andromeda, as it happens, is a quite red galaxy. Its U-B index is +0.50, and its B-V index is +0.92. That's red. Judging from its U-B and B-V indexes alone, M31 could have been a "red and dead" galaxy, without any star formation at all. It's a good thing, then, that Andromeda is so nearby, so that we can see all its young stars and emission nebulae - although no pink gas clouds can be seen in this particular image, and the large association of young stars, NGC 206, can just barely be spotted in the lower left part of the galaxy.

We may note, however, that the overall color of Comet PANSTARRS is almost the same as the overall color of Andromeda. Andromeda, admittedly, is just a tad yellower due to its bright yellow bulge. PANSTARRS is the same white color "all over", reflecting the Sun's B-V of 0.656 ± 0.005. For whatever reason, PANSTARRS apparently lacks both the typical green comet coma and a blue ion tail.

Ann

[Chris Peterson]

PANSTARRS is the same white color "all over", reflecting the Sun's B-V of 0.656 ± 0.005. For whatever reason, PANSTARRS apparently lacks both the typical green comet coma and a blue ion tail.

Visually, the Sun is white, which is most definitely not what we see with PanSTARRS. The tail is yellow because of wavelength dependent scattering, otherwise it would look much more neutral (like the Moon).

We're basically looking straight up this comet's exhaust pipe, so the foreshortened tail is blocking a good view of the coma, and probably hiding any ion tail.

[BMAONE23]

This also means that the Comet with tail is larger than 6 full moons

[neufer]

We're basically looking straight up this comet's exhaust pipe,
so the foreshortened tail is blocking a good view of the coma, and probably hiding any ion tail.

How are we "looking straight up this comet's exhaust pipe"

• (Sort of down, perhaps.)

---

<<Pan-STARRS should be visible for the next couple of weeks, moving north but getting fainter as it does so. It passed the Sun on March 10, and as it moves away the illumination drops, so it dims. As you can see in the diagram below, its orbit is nearly perpendicular to Earth’s (the dark blue line is when it was south of the Earth’s orbital plane, and light blue is north). The path it’s taking is nearly face-on to us, so it never gets any closer than it is now, and it’s moving nearly straight up, out of the Earth’s orbital plane, so the distance to it is increasing rapidly. By April it will have faded considerably, and may dim to below naked eye visibility by mid-April.>>

[LocalColor]

A wonderful photo Pavel Smilyk! Unfortunately we have tall mountains obscuring our view of this wonder.

[Anthony Barreiro]

Comet Panstarrs and the Andromeda Galaxy, two different astronomical
objects, but here they have a interesting unit of image

The Andromeda Galaxy is Messier 31. 18th century French astronomer Charles Messier created his catalogue of nebulous celestial objects to warn his fellow comet hunters about these "false comets." The telescopes Messier used probably gathered as much light as a modern 100 mm refractor or 150 mm reflector. Here's Bob King's picture of M31 and Comet PanSTARRS through a 180 mm telescope and indeed they look remarkably similar. (The weather where I live has been cloudy and rainy, so I haven't had a chance to observe this conjunction yet, and the forecast is for more rain. We need the rain, and snow in the mountains, but I would love to have a peek at this comet passing by this galaxy.)

[Beyond]

Passing by this galaxy Datsa summa comment about a comet

[Anthony Barreiro]

Passing by this galaxy Datsa summa comment about a comet

As seen from Earth, which as we know is the center of the universe.

[henrystar]

Do you know Earth Science Picture of the Day does not seem to have reader response? Their lightning over Alberta today reminds me of the Rolling Thunder (like, I mean, ROLLING THUNDER) I heard as a child on the Canadian shores of Lake Huron.

[Beyond]

Passing by this galaxy Datsa summa comment about a comet

As seen from Earth, which as we know is the center of the universe.

Ah, ok. You're excused from pulling the comets leg tail a bit,then.

[moonstruck]

Oooh.....

[fausto.lubatti]

Excellent view of two wonders of the sky!