A celestial visitor, seen from space

By Phil Plait | December 22, 2011 11:26 am

I know I post a lot of pictures I describe as amazing, lovely, breath-taking, jaw-dropping… but that’s only because it’s always true. In this case, though, I think those adjectives fall way, way short in describing the seriously paralyzing beauty of this photograph: Comet Lovejoy, as seen by an astronaut on board the International Space Station:

[Click to encomanate — and yes. you need to.]

Oh. My.

This stunning photo was taken by astronaut Dan Burbank as the ISS passed over Australia at 17:40 GMT on December 21, 2011 [update: more pix here]. It was early morning over Australia at the time, and you can see the dark limb of the Earth, the thin green line of airglow (atoms in the upper atmosphere slowly releasing the energy they accumulated over the day), some southern hemisphere stars… and of course, the incredible, ethereal, other-worldly beauty of Comet Lovejoy, its tails sweeping majestically into the sky.

Wait, what? "Tails", plural? Yup. Hang on a sec. I’ll get to that.

First, the comet was discovered by amateur astronomer Terry Lovejoy in November. It turned out to be a sungrazer, a comet whose orbit plunges it deep into the inner solar system and very close to the Sun’s surface. It screamed past our star last week, on December 15/16, and, amazingly, survived the encounter. Some sungrazers do and some don’t, but Lovejoy is bigger than usual for such a comet, and that may have helped it remain intact as it passed less than 200,000 km over the Sun’s inferno-like surface.

Now the comet is moving back out, away from the Sun and back to the frozen depths of deep space. But the Sun’s heat, even from its greater distance now, is not to be denied. Comets are composed of rock and ice — the ice being what we normally think of as liquid or gas, like ammonia, carbon dioxide, and even good ol’ water. The heat from the Sun turns that ice directly into a gas (in a process called sublimation), which expands around the solid nucleus of the comet, forming what’s called the coma. Pressure from sunlight as well as the solar wind blows this material away from the comet head, resulting in the lovely tail, which can sweep back for millions of kilometers.

But in many cases, comets have two tails: one made of dust, and another made of gas. The dust tail is made of the fine-grained rock in the comet, let loose as the ices sublimate. This material follows pretty much in the same orbit as the comet itself, so it tends to curve away as seen from Earth.

The gas, though, gets stripped of electrons by ultraviolet light from the Sun — such a gas is said to be ionized, and is called a plasma. This material is strongly affected by the Sun’s magnetic field and solar wind, which is blowing out from the Sun far faster than the comet itself is moving. Because of this, the ion tail tends to be fairly straight, and point directly away from the Sun. I’ve highlighted Lovejoy’s ion tail in the picture above, stretching the brightness so it’s easier to see.

The ion tail was more obvious just a few days ago, as you can see in this shot taken from the NASA/ESA SOHO solar observatory on December 17 at 06:54 GMT:

The Sun is behind a mask to block its light, and you can see the streamers of the solar wind blowing from it. The comet is on the lower right — the horizontal line going through it is not real, but due to the comet’s brightness flooding the digital detector in SOHO’s camera –and the two tails are easy to see. Many comets display two tails like this, depending on their composition and the conditions in the solar wind at the time. It looks like Lovejoy’s is fading now, but clearly the dust tail is still spectacular.

Right now, Lovejoy is only really visible from the southern hemisphere. If you live Down Under, then getting up an hour or so before sunrise over the next few days will afford you a fantastic view you don’t get too many times in your life. You should take it.

For more stunning views and descriptions of Lovejoy, see the Universe Today website and The Planetary Society Blog.

Image credit: NASA/Dan Burbank c/o Fragile Oasis; NASA/ESA/SOHO/Helioviewer.org

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

Comments (29)

  1. Chris

    Wow, simply wow.
    Yet another picture you could have had in your 2011 gallery.

  2. Ganzy

    Stunning image! I don’t suppose there is any chance that Earth will sweep through those dusty leftovers at any point in time? Would make for a great display if it did.

    I wonder how many tons of dust it would be dumping over say 1000km of passage. Is it possible to work something like that out? And would it be tons, or just hundreds of kilos?

  3. Chris

    @3 Ganzy
    Lovejoy’s orbit doesn’t intercept our own. In fact it’s way below the earth’s orbit. The inclination to ecliptic is 134.4° and if you look on JPL Small-Body Database Browser, you can see the comet sadly is nowhere near us.

  4. Jon Hanford

    There’s a great time-lapse video by Colin Legg showing the comet rising over Western Australia, taken about the same time as the ISS image: http://vimeo.com/34007626

    You can clearly make out the dust and gas tails in the video.

  5. Ganzy

    That’s a shame Chris, thanks for the heads up on SBDB anyway.

  6. John Baxter

    Aside: when I encomanated the image, Google cleverly asked “Is this John?”. Actually no, it isn’t–I only have one tail and it is shorter than that.

    Wonderful image. I’m happy that some of the world is able to enjoy the show directly.

  7. bouch

    I love that there is almost no light visible on the earths surface. Those lucky enough to be in an area that dark must have a wonderful view of Lovejoy.

  8. Chet Twarog

    Reminds me of Comet McNaught that had a more extensive fanned tail and seen in the Northern Hemisphere as well as the Southern.

  9. Oh man, there has been NO media about Lovejoy in Australia. I’ve set my alarm for 4:30 tomorrow morning and I’ll be up on the roof taking a gander at it.

  10. Ragutis

    Speaking of cool pics, Phil, have you seen the gallery of lenticular clouds over at the BBC today?


  11. J

    Rev. Lovejoy, from the Simpsons?

  12. Naomi

    Ooh. I will definitely be getting up early tomorrow – and hoping it’s not overcast!

  13. Grendel

    I am in Western Australia and I have just set my alarm for 4am tomorrow and arranged my Galileoscope and other small viewing devices and a camera for quick grabbing.

    I have a limestone outcrop nearby that gets me just above the level of the local street lamps with a good view east. Like Naomi I hope it is not overcast!

  14. Crux Australis

    My local paper described Terry as an astrologer. Sheesh. This even after interviewing a local astronomer.

  15. Messier Tidy Upper

    Superbly magnificent photos. I think we have a winner for next years best astronomical images already here – or in the subsequent time lapse post if that counts. :-)

    If you live Down Under, then getting up an hour or so before sunrise over the next few days will afford you a fantastic view you don’t get too many times in your life. You should take it.

    Yep. I’m going to be doing that alright. I’ll get up pre-dawn tomorrow for it. For once I won’t be too busy. Christmas has come early astronomy~wise with this. :-)

    @ 9. Chet Twarog :

    Reminds me of Comet McNaught that had a more extensive fanned tail and seen in the Northern Hemisphere as well as the Southern.

    Comet McNaught* remains the best comet I have ever seen in my life so far. I really hope Comet Lovejoy manages to come somewhere close! :-)


    * Comet McNaught the Great Comet of 2007 that is – there were actually a number of comet McNaughts named after their Aussie discoverer Robert. BTW. I don’t think supermodel celebrity Erin McNaught is his daughter but I could be wrong.

  16. Amazing picture!

    But funny are some comments from people, sad because a 500m (core) comet isnt comming close to us. o.O :)

  17. SkyGazer

    WOW! Jawdroppingly beautiful!
    What a view from the office those guys have.

  18. Phil,

    The picture is absolutely stunning. I saw it last night and when I went to find it again today ended up at the Discovery Channel site by accident. They have the same picture posted, but the tail of the comet is pointing up instead of down.

    I realize tehre really is no up or down in space, but i am curious as to how the Astronaut Burbank would have seen it.

    All the best,

  19. flightmaniac

    Is it bad that I read “Oh. My.” in George Takei’s voice?

  20. What I seen early morning hours in Sacramento Calif was far more beautiful than the pics I’ve seen thus far. I was wondering if anyone seen what I did. The sun’s light must’ve hit this comet’s tail precisely to illuminate the awesome colors.

  21. Finally saw comet Lovejoy myself in person this morning! 😀

    (After three or four mornings of getting up pre-dawn especially to see it and being thwarted by clouds.)

    Saw it 3.40 am till just before 5.00 am Adelaide (Australian) time. Beautiful etheral sight. Just below the Southern Cross stretching up to Alpha Centauri from just above the horizon. All straight tail not much if any head or comae apparent looks almost like a faint narrow contrail very diffuse but still easily visible to unaided eye. Length is about double the distance of the pointers. (Alpha & Beta Cen) Disappears very quickly into dawn twilight whilst stars remain visible even Epsilon Crucis. (BTW. Kaler’s Eps Crucis entry is linked to my name here in case that helps. 😉 )

    Comet McNaught (2007) was much brighter – that was visible over the Adelaide oval during dusk at one cricket game with the oval lights on and all – but still one of the brightest and best comets I’ve ever seen & certainly the best since then. :-)


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