Desktop Project Part 8: From filament to prominence

By Phil Plait | April 2, 2012 7:00 am

[Over the past few weeks, I’ve collected a metric ton of cool pictures to post, but somehow have never gotten around to actually posting them. Sometimes I was too busy, sometimes too lazy, sometimes they just fell by the wayside… but I decided my computer’s desktop was getting cluttered, and I’ll never clean it up without some sort of incentive. I’ve therefore made a pact with myself to post one of the pictures with an abbreviated description every day until they’re gone, thus cleaning up my desktop, showing you neat and/or beautiful pictures, and making me feel better about my work habits. Enjoy.]

Sometimes, what you see depends on how you see it.

For example, take the Sun. Imagine it as a ball of ionized gas 1.4 million kilometers in diameter, churning and roiling, with intense magnetic fields piercing its surface and causing vast eruptions of material 150,000 km across.

OK, you don’t have to imagine that, since a) that’s the way the Sun really is, and 2) I can show you a picture of it! Like this one, from astrophotographer Ted Wolfe:

That shows the Sun as it was on November 25, 2011. That towering arc is plasma — gas that has had one or more electrons stripped from its atoms — being guided by the crazy strong and complex magnetic fields looping into and out of the Sun’s surface. This picture is interesting, since this loop of plasma is nearly aligned with our line-of-sight. One foot of it is on the near side of the Sun, and it arcs over across the Sun’s limb to the other side!

What’s funny is that when you get one of these on the face of the Sun it’s called a filament. When it’s seen projected against the black of space, it’s called a prominence. This terminology is a holdover from a long time ago, but we still use it. To be fair, the terminology comes up because usually filaments look very different than prominences. If you use a regular filter (one that just blocks light) to take pictures of the Sun, filaments look dark; they are cooler than the Sun’s surface and absorb the light from coming up from beneath (much like sunspots). But they’re still plenty hot, and look bright when seen against the black of space. You can see examples of this here and here.

This picture from Ted Wolfe is different. He used a special Hα filter, which doesn’t just darken the Sun but picks out a very specific color of light (in the red part of the spectrum) and isolates that, letting it through while blocking everything else. Warm hydrogen (like in the filament) emits that color, so if you use that filter the loop of plasma looks pretty much the same against the Sun as it does against the sky. It’s a bit of a trick, but is useful in showing that filaments and prominences are just two different views of the same structure.

So what do we call this thing in Ted’s picture? We see it against the Sun and against space! A filanence? A prominent? Beats me. But it’s pretty cool either way.

Credits: Tom Wolfe, used by permission.


Related posts:

The Sun roils over Mexico
The delicate tendrils of a solar dragon
A fiery angel erupts from the Sun
Seriously jaw-dropping picture of the Sun

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures
MORE ABOUT: filament, prominence, Sun

Comments (9)

  1. Nigel Depledge

    But they’re still plenty hot, and look bright when seen against the black of space.

    [. . . ]

    But it’s pretty cool either way.

    Oh, wow. Simultaneous hot and cool.

    But, seriously, BA, which is it?

  2. Gary Ansorge

    I LOVE these photos.

    Thanks,

    Gary 7

  3. Oh, suuuure, we still say “filament” and “prominence,” but Pluto’s no longer a planet. Where’s the justice..?!

  4. Rich

    It’s a filament, it’s a prominence, it’s a filanence!

  5. Rakesh

    You can clearly see that the prominence moves from dark to bright as it moves from disk to limb.

  6. I used to get that “filimence” effect with a B&W video camera and Hα-filtered telescope at a museum where I worked by fiddling with the contrast and gain on the camera. The resulting image on the exhibit screen was very low contrast but sometimes you could see one leg of a prominence that was *just* in the right place also show up as a filament against the surface.

    This image is way superior, of course. Kids today …

  7. Messier Tidy Upper

    @ ^ Unclaimed Mysteries & #4. Rich :

    It’s a filament, it’s a prominence, it’s a filanence!

    Nice term ‘filamence’ – I’m gunna use that! Cheers! ;-)

    @3. Mooncity :

    Oh, suuuure, we still say “filament” and “prominence,” but Pluto’s no longer a planet. Where’s the justice..?!

    Hey, just because the IAU can’t tell a planet from a pizza doesn’t mean we have to go along with them! ;-)

    I, for one, still count Pluto as a planet – as well as the other ice dwarf planets including Eris and Ceres. I fully expect the dreadful, current IAU definition will one day be revised and replaced with a better alternative. The sooner that happens, the better. (Don’t get me started!)

    Back on topic – yup. Great image. :-)

    The Sun looks awfully yellow for a Hydrogen alpha filter though – doesn’t our daytime star usually appear very crimson red as seen at that wavelength?

  8. reidh

    It occurs to me, that the sun is a perfect “picture” of the famous Lake of Fire that God is going to throw all of the useless souls of the dead into at the end of Time.

  9. Nigel Depledge

    MTU (7) said:

    I, for one, still count Pluto as a planet – as well as the other ice dwarf planets including Eris and Ceres.

    Trying to be brief here, for the sake of other commenters:

    As far as the IAU are concerned, you don’t matter.

    As far as casual conversation is concerned, the IAU technical definition doesn’t matter.

    I fully expect the dreadful, current IAU definition will one day be revised and replaced with a better alternative.

    You have yet to demonstrate that there is anything wrong with the IAU definition, despite the many many occasions on which you have railed against it.

    Sure, you have tried, but your arguments are all weak, and you have yet to address even one of my criticisms of your arguments, except (effectively) to say “but it’s still a planet”.

    Your suggested alternative has bigger flaws than the present IAU definition and is in no way superior, to whit:

    1. It contains exactly the same logical flaws and need for pragmatism as the IAU definition (so is not superior from a logical viewpoint, despite your claim to the contrary).
    2. It fails to recognise the huge disparity in the level of knowledge between our solar system and all other planetary bodies elsewhere in the galaxy.
    3. It fails to recognise that our solar system contains a clear and natural discontinuity between the eight bodies (not counting the sun) that are obviously unique and bodies like Ceres and Pluto that are – as far as anyone can tell – simply the largest examples of classes of similar objects. It was Pluto’s obvious lack of uniqueness that sparked the need to define the term “planet” in the first place.

    The sooner that happens, the better. (Don’t get me started!)

    Well, this time it was you who invaded Poland.*

    * Yes, it’s a reference to Fawlty Towers.

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