Tag: comets

The softly glowing zodiac: lesson learned

By Phil Plait | July 12, 2012 6:57 am

Every day I post a short, pithy astronomy or space fact on Twitter and Google+. I call them BAFacts, and I have them all archived here on the blog. I try to make them as accurate as possible within the limitation of 140 characters. But I wrote one recently that, as it turns out, I had to retract for being incorrect. And I’m happy about it! Here’s why.

I recently was going through old posts and saw one that mentioned zodiacal light, a very faint glow in the sky that can only be seen on very dark nights. It’s a band of light that follows the path of the planets across the sky, which is technically called the ecliptic. It passes through the constellations of the zodiac, hence its name*.

This picture of the zodiacal light is by friend of the BABlog Brad Goldpaint [click to embiggen, and note this is a part of a larger shot that’s breathtaking]. The two bright "stars" are Venus and Jupiter, and you can see the glow from zodiacal light reaching up and to the left, following the ecliptic.

The origin of zodiacal light (when I learned about it, years ago) was thought to be dust from asteroid collisions. Asteroids out past Mars orbit pretty much in the same plane as the planets. When they smack into each other – and they do – they make dust. This reflects sunlight, so we’d see it as a faint band of light across the ecliptic. Case closed!

Of course, regular readers know me better than this. Read on!

Read More

Amazing video of comet on a solar death dive

By Phil Plait | June 13, 2011 6:30 am

Last month, on May 10/11, a bright comet took the Final Plunge, dropping into the Sun. It either broke up and evaporated or actually impacted the Sun, because it wasn’t seen to reappear around the other side. Here’s the video, taken using NASA’s SOHO satellite:

Pretty cool! You can see the Sun erupting with a coronal mass ejection, too. It’s tempting to wonder if the two are related, but in fact the CME let go before the comet had even had a chance to interact with the Sun’s magnetic field (CMEs are essentially magnetic events). I know there are tracts floating around the ‘net about comets causing solar events, but the folks promulgating such ideas never do any actual statistics. They see a comet plunge into the Sun, see a flare or CME, and say they’re related. However, you have to look at how many events happen without comets nearby, and more importantly how many comets hit the Sun and don’t spark an event. Without that, you’re just cherry-picking.

Incidentally, you may have noticed a very short horizontal line going right through the heart of the comet. That’s not real; it’s an artifact of the detector on SOHO. It’s called blooming, and it has nothing to do with Planet X unless you’re willing to turn your back firmly on reality.

Anyway, comets hit the Sun quite often; many have similar orbits and are called Kreutz family comets. It’s funny: many of them get bright enough to technically be seen by the eye, but they’re so close to the Sun they still get washed out.

Actually, now that I think about it, I should mention that SOHO is the greatest comet finder of all time; over 2000 comets have been seen in SOHO images! It seems funny to look to the Sun to find comets, but it’s also amazing to me to think that those 2000 comets have been seen in only 16 years since SOHO’s launch… think about how many comets are out there, in deep space. Millions. Billions. More.

We live in an amazing place, and in an amazing time that we can discover so much about it.

Science! I love this stuff.


CATEGORIZED UNDER: Astronomy, Cool stuff, Debunking, Science
MORE ABOUT: blooming, CME, comets, Planet X, SOHO

The WISE family comets

By Phil Plait | June 3, 2011 7:00 am

In the little over one year that the Wide-field Infrared Survey Explorer (WISE) spacecraft surveyed the sky, it captured images of hundreds of millions of objects. Many of these were previously known stars, galaxies, and the like, but it also added a few newcomers to our catalogs, including a score of comets:

[Click to encomanate.]

Why did WISE find them, and not ground-based observers? Lots of reasons come to mind. Comets are not really the spectacular and brilliant objects commonly thought; at least, not all of them are. The solid part of a comet is usually a mix of rock and ice, the ice being made of water, ammonia, carbon dioxide, and other materials we tend to think of as gases here on Earth. But in the depths of space, where it’s cold, they can remain frozen solid… until the comet nears the Sun. Then, the materials go from a solid directly to a gas, surround the solid nucleus, and reflect a whole lot more sunlight. The comet gets bright and can be spotted more easily.

Even then, it may not be easy. The comet may be small and faint in optical light. It may be too near the Sun to spot. It may be too far away to be seen easily. Or it may simply not be in a place anyone on Earth is looking.

WISE scanned the entire sky, and was prone to seeing such things. And the lack of optical light isn’t so much an issue if the comet is warm enough to glow in the infrared, and that can be at temperatures a hundred degrees below 0 or more. And even then, WISE only found 20 such comets before anyone here on Earth did. I’ll note it also did see quite a few comets discovered on Earth first, like the comet C/2007 Q3, also known as Siding Spring.

It also racked up a huge number of previously unknown asteroids, some of which are potentially dangerous to the Earth some time in the (far, hopefully) future. The point is — and I’ve said this many times before — the more eyes we have on and in the sky, the better. And by looking at different wavelengths we’ll see even more.

Image Credit: NASA/JPL-Caltech/UCLA

Related posts:

The first spectacular views of the sky from WISE
WISE uncovers its first near-Earth asteroid
A taste of WISE galaxies
Orion’s WISE head

CATEGORIZED UNDER: Astronomy, Pretty pictures
MORE ABOUT: comets, infrared, WISE

Think comets are cool? Tweet about them!

By Phil Plait | May 31, 2011 11:25 pm

The European Space Agency is sponsoring a contest: if you think comets are cool, tweet about them! The winner gets a trip to Darmstadt, Germany — ESA’s operating HQ — to celebrate 25 years of exploring comets.

There are rules, but they boil down to posting on Twitter about comets, using the "#coolcomet" hashtag, and providing an optional link to a non-text page (YouTube video, picture, etc.) that follows up. You have to be from a member country of ESA or the US to participate.

They are collecting all the tweets using TwapperKeeper, and you can see what others have done. They’re getting lots of entries, so if you want to try, I suggest being clever. Think about different aspects of comets, something unusual, and why they’re so interesting. The posts linked below might help get your unsublimated gases thawed.

Have fun! And if you win, send me a postcard from Darmstadt.

Image credit: Comet McNaught in the daytime from Chris North/Wikipedia

Related posts:

Ten Things You Don’t Know About Comets
Followup: Deep Impact crater on Tempel 1
A comet creates its own snowstorm!
Amazing close ups of comet Hartley 2
Actually, if you’re a comet, it *is* easy being green

CATEGORIZED UNDER: Astronomy, contest, Cool stuff, Space

Ashes to ashes, stardust to stardust

By Phil Plait | April 12, 2011 7:00 am

On March 24, the NASA mission Stardust ran out of fuel and sent its last data to Earth. At 16:33 Pacific time the mission was officially ended.

Launched in 1999, Stardust became a wildly successful mission. It passed by the asteroid Annefrank, sampled the dust from one comet (Wild 2) — returning those samples to Earth in a special re-entry container while the spacecraft itself flew on — and looked closely at another (Tempel 1) to see the crater left by the Deep Impact mission.

It’s always sad to see a mission end, but I like to also keep my eyes ahead. Stardust may be done, but Rosetta flies on, heading toward a rendezvous with a comet where it will deploy an actual lander. The Dawn spacecraft will enter orbit around the main-belt asteroid Vesta later this year as well. And, of course, MESSENGER is now orbiting Mercury and returning data.

We learned a lot from Stardust, and we get better with this endeavor of solar system exploration as a result.

And that’s the whole point, isn’t it?

Image credit: NASA/JPL-Caltech

Related posts:

Followup: Deep Impact crater on Tempel 1
Stardust snaps close-ups of a second-hand comet!
A comet creates its own snowstorm!
The return of Stardust
Stardust@Home starts NOW


Angry comet is angry

By Phil Plait | March 1, 2011 7:00 am

A couple of weeks ago, the space probe Stardust passed by the comet Tempel 1. While I was perusing the NASA images, I found this one:

I couldn’t help but notice the comet seemed a little angry. I made it a little more obvious:

Of course, if someone smashed a 370 kilo block of copper into me at 10 times the speed of a rifle bullet, I’d be pretty angry myself!

Related posts:

Stardust snaps close-ups of a second-hand comet!
Followup: Deep Impact crater on Tempel 1
Ten Things You Don’t Know About Comets
3D House of Comet Nucleus!

MORE ABOUT: comets, Stardust, Tempel-1

No, there's no proof of a giant planet in the outer solar system

By Phil Plait | February 14, 2011 2:30 pm

I’m getting a lot of email and tweets about NASA supposedly having proof of a giant, Jupiter-sized planet orbiting the Sun way beyond Pluto. Let me be clear: while certainly possible, this idea is not at all proven, and in my opinion still pretty unlikely. As usual, this started as a more-or-less accurate media story and is getting inflated as it gets re-reported. As far as I can tell, the original report was in the UK paper The Independent.

Here’s the deal. Two astronomers, John Matese and Dan Whitmire, have theorized about the possibility of a previously-undiscovered planet way beyond Pluto for some time. This is not a crazy idea; we see planets orbiting other stars way out, and there’s other evidence big planets can be pretty far out from the Sun (mind you, evidence does not mean proof). As it happens, there are lots of chunks of ice orbiting the Sun pretty far out as well. Some of these have orbits which bring them into the inner solar system, and we see them as long-period comets.

What Matese and Whitmire did was wonder how a big planet would affect the orbits of these comets. If you measured enough of them, would you see the effects of the gravity of this planet? They claim you can, and even gave the planet a tentative name: Tyche.

I read their papers, and thought the data were interesting but unconvincing. The sample size was too small. A bigger study was done, but again the effects weren’t quite enough to rise to the level of breakthrough. I’m not saying the astronomers are wrong — the data were certainly provocative, and potentially correct! Just not firm enough. Read More

CATEGORIZED UNDER: Astronomy, Piece of mind, Skepticism
MORE ABOUT: comets, planet, Tyche

Top Ten Astronomy Pictures of 2010 – Runners Up

By Phil Plait | December 20, 2010 6:30 am

When I made my Top 14 Astronomy Pictures of 2010, it was really tough cutting some out. This is a gallery of the images that, for whatever reasons, I decided to leave off. They’re still spectacular and gorgeous, though! Click on the thumbnail in the slider to go to an image, use the arrows to navigate back and forth, and click on the big image displayed below to get more info and a bigger version if available.


CATEGORIZED UNDER: Astronomy, Pretty pictures, Top Post

Asteroid comparison chart, Part II

By Phil Plait | December 9, 2010 6:50 am

I’ve been meaning to let y’all know about this: a while back I wrote how Emily Lakdawalla of the Planetary Society blog put together a scaled asteroid/comet size comparison chart. Well, she’s updated it to include the nucleus of Hartley 2, visited by the EPOXI spacecraft last month.


The arrow points to the new addition of Hartley 2. It’s tiny! Well, compared to Lutetia, an asteroid well over 100 km across. Mind you, this chart shows every asteroid and comet we’ve ever visited and photographed with spacecraft! That’s 14 in total; I don’t know whether to be amazed that it’s that many, or sad that it isn’t more. Maybe a little of both. But Dawn will visit the asteroids Ceres and Vesta starting next year. More comets are coming up too, which means more incredible pictures and important science is coming up in the near future, too. And that’s definitely good news.

Here are some other images of the comet Hartley 2. Use the thumbnails and arrows to browse, and click on the images to go through to blog posts with more details and descriptions.



CATEGORIZED UNDER: Astronomy, Pretty pictures

Arecibo gives comet some radar love

By Phil Plait | October 29, 2010 10:42 am

Using a giant radio telescope like a cop’s radar gun, astronomers have made some pretty cool images of the nucleus of the comet Hartley 2:


Hartley 2 is a comet that is currently very close to the Earth as these things go: last week it passed us at a distance of about 18 million km (11 million miles). Astronomers took advantage of the close pass to ping the comet with radar pulses. By timing exactly how long it took the pulses to go from the telescope to the comet and back to Earth, they can create a map of the comet’s shape and other characteristics — something like how dolphins and bats use echolocation to map their surroundings… though, as Emily Lakdawalla at The Planetary Society Blog explains, it’s a bit more complicated.

From the images, it looks like the nucleus — the solid, central part of a comet — is highly elongated, about 2.2 km (1.4 miles) in length, and rotates once every 18 hours. We’ve only seen a handful of comets up close, and in general the nuclei are potato-shaped, so this one fits that description. The image has a scale of about 75 meters per pixel.

These observations were made to help out the EPOXI space mission, which will pass just 700 km (420 miles) from the nucleus of Hartley 2 on November 4. That means we’ll be getting some really cool close-up images and data from the comet very soon! Stay Tuned.

MORE ABOUT: Arecibo, comets, Hartley 2, radar

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