As promised: Jupiter and moons seen by SOHO

By Phil Plait | May 17, 2012 1:56 pm

A little while back, I wrote about Jupiter appearing in an image from NASA’s SOHO Sun-observing satellite. I promised that it would soon appear in a SOHO camera that had higher magnification, and we’d be able to see its moons.

I am not one to break promises:

Awesome. It helps to set the resolution to 720p to see the moons when they’re pointed out.

And just you wait: in early June, Venus will appear in the LASCO C3 and C2 cameras, on its way for a date transiting the Sun for the last time in over a century. I’ll have more about that event in a few days… I promise!

Tip o’ the occulting bar to SungrazerComets on Twitter.

Related Posts:

- Jupiter, acting all superior
- Lovejoy lives!
- The Sun fries a comet and we got to watch
- The Galilean Revolution, 400 years later

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures
MORE ABOUT: Callisto, Ganymede, Jupiter, SOHO, Sun

Jupiter, acting all superior

By Phil Plait | May 6, 2012 7:00 am

This is a cool picture:

What you’re seeing is from the NASA/ESA satellite Solar and Heliospheric Observatory, or SOHO. It stares at the Sun all the time, monitoring its activity. This image, from May 3, 2012 is from the LASCO C3, one of the cameras on board. It has a little metal paddle (called an occulter) to block the ferocious light of the Sun; that’s the black bar and circle. The white outline is the position of the Sun and its size in the image.

You can see an emerging coronal mass ejection on the left: that’s the bulb-shaped thingy. It’s actually an incredibly violent expulsion of a billion tons of subatomic particles hurled away at high speed due to the explosive discharge of the Sun’s magnetic field… but that’s not why I posted this picture.

You can also see streamers coming from the Sun; those are places where particles flow freely into space from the Sun. Basically, the magnetic field of the Sun trails into space in those locations, allowing the wind to escape. But that’s not why I’m showing you this picture, either.

Look on the left. See that weird dot with the horizontal line through it? That’s Jupiter! The line is not real; it’s where the camera got overexposed by the planet (digital detectors — like your phone camera — convert photons of light into electrons, and if a source is too bright, the electrons overflow the pixels like water from a bucket. The way the camera works, the electrons flow along the horizontal grid of pixels, creating these lines. This is called "blooming").

Jupiter has been gracing our sky for months, but has been getting further west every night, closing the apparent distance between it and the Sun. It’s on the opposite side of the Sun from us, at a distance of almost 900 million kilometers (550 million miles). When two objects get close in the sky, it’s called a conjunction. When it’s a planet on the far side of the Sun, it’s called superior conjunction. Just so’s you know.

Anyway, I just think this is neat. Jupiter is roughly one-billionth as bright as the Sun, yet there it is in the picture! And even though SOHO is designed to look at the Sun, Jupiter is so bright it’s overexposed. Imagine if the spacecraft moved a bit and the Sun were to peek out from behind the occulter… which can happen. SOHO goes into "safe mode" when that happens, shutting down systems that might get damaged. Every astronomical satellite has contingency plans like that, since it’s hard to send a repair service to most of ‘em. Generally it’s fixable by sending software commands to the spacecraft once the underlying problem has been ascertained.

If you want, SOHO has images online that are updated constantly. Go see what the Sun is doing now! Over the next few days Jupiter will get closer to the Sun, then pass very close to or even behind the disk. LASCO 2, another camera on SOHO that has a smaller field of view but a bit more resolution, should show the moons too when Jupiter moves into its field. I’ll post again when that happens. That’ll be even neater.

Image credit: NASA/ESA/SOHO

CATEGORIZED UNDER: Astronomy, Pretty pictures

The Sun is 1,392,684 +/- 65 km across!

By Phil Plait | March 21, 2012 7:00 am

You would think that, of all the astronomical measurements we could make, one of the best known would be the diameter of the Sun.

You’d be wrong. It’s actually really hard to measure! For one thing, we sit at the bottom of an ocean of air, gas that is constantly moving around, mucking up precise measurements. For another, our telescopes themselves can be difficult to calibrate to the needed accuracy to get a really solid measurement of the size of the Sun.

Nature, however, provides us with a way to measure our nearest star. Naturally! And it involves Mercury, the smallest and, critically, the closest planet to the Sun.

In 2003, and again in 2006, Mercury passed directly across the face of the Sun as seen from Earth (the picture above is a view of the 2006 transit as seen by SOHO; a very short animation was made from this as well). Mercury’s orbit is tilted a little bit with respect to Earth’s, so these transits don’t happen terribly often, occurring only every few years. But because we know the orbit of Mercury so well, and our own distance from the Sun, by precisely timing how long it takes the diminutive world to cross the Sun, we can get a very accurate measurement of the Sun’s diameter.

A team of scientists did exactly this, using SOHO, which is a solar observing and solar-orbiting satellite. Because it’s in space, it doesn’t suffer from the problems of peering through a murky, dancing atmosphere. They were able to measure the timing of Mercury’s passage of the Sun to an accuracy of 3 seconds in 2003 and 1 second in 2006. They had to take into account a large number of effects (the Sun’s limb is darker than the center, which affects timing; they had to accurately measure the position of Mercury; they had to account for problems internal to SOHO like focus and the way it changes across the detector; and, of course, correct for the fact that Mercury cut a chord across the Sun and didn’t go straight across the diameter — but that only took knowledge of Mercury’s orbit and some trig) but when they did, they got the most accurate measure of the Sun’s diameter ever made: 1,392,684 +/- 65 km, or 865,374 +/- 40 miles.

That uncertainty of 65 km is quite a it better than what can be done from the ground, amazingly. It may sound like a lot, but it actually represents an accuracy of 99.995%! The Sun is big. Really, really big.

… and they’re not done. The authors are going to observe the Transit of Venus coming up in June, hoping it’ll improve their measurements. I’ll be very curious to see how that goes; Venus has an atmosphere which I would think would confound the observations. They may have ways around that though.

Either way, I think this is completely fascinating. Even thrilling! The Sun is the brightest thing in the sky, the center of our solar system, the basis of light and heat and life on Earth, and the best-studied star in the Universe.

And here we are, just now figuring out how big it is. Sometimes the simplest things can be the hardest, I suppose.

Image credit: NASA/EDA/SOHO

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CATEGORIZED UNDER: Astronomy, Cool stuff, Science, Top Post

The Sun ate another comet

By Phil Plait | March 16, 2012 7:00 am

It’s tough to be a comet.

You spend most of the time — billions of years, really — out in deep space where it’s cold and dark. Of course, since you’re mostly made of ice, that’s not so bad. After all, the Sun is hot, and if you venture too close…

Well, you know what happens then. And such was the fate of Comet SWAN, discovered just a few days ago as it plunged headlong into the seething fires of the Sun. And I have video!

That was made from images taken by NASA’s SOHO satellite. In fact, the comet is named SWAN because it was first seen in the SOHO SWAN camera, designed to look for ultraviolet light coming from hydrogen. Here’s the thing: no comet has ever been seen before in that camera, including the phenomenally bright comet Lovejoy from a few months ago. But Lovejoy got incredibly bright overall, while this new comet never did brighten much. Comet SWAN must have undergone some sort of outburst to make it so bright and then fade again; that’s happened before.

Here’s another shot of it from SOHO:

[Click to enhalleyenate.]

Comets like these are called Kreutz family Sun grazers, a collective group of comets on similar orbits that take them very close to the Sun’s surface. Some survive, like Lovejoy did, and some… don’t.

The Sungrazing Comets site has lots more info on this weird comet and its untimely death. You can also follow SungrazerComets on Twitter for current news on these doomed chunks of ice.

Image credit: NASA/SOHO. Music in the video was "Heavy Interlude" by Kevin MacLeod, used under Creative Commons license from incompetech.com.

Related Posts:

- Amazing video of comet on a solar death dive
- The comet and the Coronal Mass Ejection
- Amateur astronomer discovers sungrazing comet
- One more Lovejoy time lapse… maybe the last

The Sun aims a storm right at Earth: expect aurorae tonight!

By Phil Plait | January 24, 2012 6:00 am

Around 04:00 UTC on Monday morning, January 23, 2012, the Sun let loose a pretty big flare and coronal mass ejection. Although there have been bigger events in recent months, this one happened to line up in such a way that the blast of subatomic particles unleashed headed straight for Earth. It’s causing what may be the biggest space weather event in the past several years for Earth: people at high latitudes can expect lots of bright and beautiful aurorae.

I’ll explain what all that is in a second, but first here’s a video of what this looked like from NASA’s SOHO satellite.

Wow! Make sure you set it to high def.

So what happened here? The sunspot cluster called Active Region 11402 happened.

Sunspots are regions where the magnetic field lines of the Sun get tangled up. A vast amount of energy is stored in these lines, and if they get squeezed too much, they can release that energy all at once. When this happens, we call it a solar flare, and it can be mind-numbing: yesterday’s flare exploded with the energy of hundreds of millions of nuclear bombs!

In the image above, the sunspots are caught in mid-flare, seen in the far ultraviolet by NASA’s Solar Dynamics Observatory (it’s colored green to make it easier to see what’s what). We think of sunspots as being dark (see the image of AR 11402 below), but that’s only in visible light, the kind we see. In more energetic ultraviolet light, they are brilliant bright due to their magnetic activity.

A huge blast of subatomic particles was accelerated by the explosion. The first wave arrived within a few of hours of the light itself… meaning they were traveling at a significant fraction of the speed of light!

But shortly after the flare there was a coronal mass ejection: a larger scale but somewhat less intense event. This also launches particles into space, and these are aimed right at us. The bulk of the particles are traveling at slower speeds — a mere 2200 km/sec, or 5 million miles per hour — and is expected to hit us at 14:00 UTC Tuesday morning or so. That’s basically now as I write this! Those particles interact with Earth’s magnetic field in a complicated process that sends them sleeting down into our atmosphere. We’re in no real danger from this, but the particles can strip the electrons off of atoms high in the air, and when the electrons recombine the atoms glow excite the electrons in atoms high in the air, and when the electrons give up that energy the atoms glow. That’s what causes the aurorae — the northern and southern lights.

If you live in high latitudes you might be able to see quite the display when it’s dark — people in eastern Europe and Asia are favored for this, since this happens after sunset there. But the storm is big enough and will probably last long enough that everyone should check after dark: look north if you live in the northern hemisphere and south if you’re south of the Equator. There’s no way in advance to know just how big this will be; it might fizzle, or it might be possible to see it farther away from the poles than usual. Can’t hurt to look! Also, Universe Today has been collecting pictures of aurorae from the solar blast earlier this week. No doubt they’ll have more from this one as well.

Although big, this flare was classified by NASA as being about M9 class — powerful, but not as energetic as an X class flare. One of those popped off last September, and shortly after that a smaller M flare erupted, which also triggered a gorgeous plasma fountain called a filament on the Sun’s surface.

As I said, we’re in no real danger here on Earth, and Universe Today has a good article describing why the astronauts are probably not in danger on the space station, either. Even if this were larger storm, the astronauts can take shelter in more well-protected parts of the station, too. Bigger storms can hurt us even on Earth by inducing huge currents in power lines which can overload the grid. That does happen — it happened in Quebec in March of 1989 — and it may very well happen again as the Sun gets more active over the next few years. [UPDATE: a ground current surge from today's event was reported in Norway.]

But we should be OK from this one. If you can, get outside and look for the aurorae! I’ve never seen a good one, and I’m still hoping this solar cycle will let me see my first.

Image credit: NASA/SOHO; NASA/SDO

Related posts:

- Awesome X2-class solar flare caught by SDO
- Gorgeous flowing plasma fountain erupts from the Sun
- NASA’s guide to solar flares
- The comet and the Coronal Mass Ejection

The Sun fries a comet and we got to watch

By Phil Plait | January 19, 2012 4:11 pm

In July of last year, I wrote about a comet that passed extremely close to the Sun. Astronomers have now had a chance to pore over that data, and were able to determine some very cool stuff.

First, here’s the video of the comet’s fiery demise (watch it in HD to make it easier to spot the comet):

See it? It’s faint, but there. Actually, there are a lot of observations from multiple observatories and detectors, which allowed astronomers to find out quite a bit about this doomed chunk of ice and rock.

For one thing, it was screaming along at about 650 kilometers per second (400 miles/second) as it flamed out. To give you an idea of how flippin’ fast that is, it would’ve crossed the entire United States in about eight seconds.

Yeah, I know.

It also passed an incredible 100,000 km (62,000 miles) above the Sun’s surface. Have you ever stood outside on a hot day, and thought the Sun would cook you? Now imagine the Sun filling half the sky. That’s what that comet saw. No wonder it disintegrated.

As it approached the Sun, it was watched by NASA’s Solar Dynamics Observatory. In its final 20 minutes or so, the comet broke up into a dozen pieces ranging from 10 – 50 meters in size (and no doubt countless smaller ones too small to detect), with a tail of vaporized material streaming behind it that went for thousands of kilometers. For that size, it would’ve had a mass of hundreds of thousands of tons — about what a loaded oil tanker weighs on Earth!

We’ve learned a lot about how comets break up and disintegrate by observing this event, but it’s raised further questions: like, why did we see this at all? Comets are faint, and to be able to see it this way against the bright Sun is odd. It was definitely one of the brightest comets seen, but it’s interesting to me that it appears to glow in the ultraviolet, as it did in the above video. That means, at that wavelength, it was brighter than the Sun! It wasn’t like a meteor, burning up as it slammed through material, so some other process must have affected it. I suspect that the Sun’s strong magnetic field may have had something to do with it; in the far ultraviolet magnetism is a strong player. Gas under the influence of intense magnetic fields can store a lot of energy, which is why sunspots — themselves the product of magnetic squeezing — look bright in UV.

Perhaps as the comet broke up, the particles inside got excited by the magnetic fields of the Sun and glowed. I’m no expert, and I’m spitballing here. The thing is, no one is exactly sure. But that doesn’t mean we won’t find out. Nothing makes a scientist’s noggin itch as much as a mystery like this, something apparently misbehaving.

One of the single most important words in science is "yet". We don’t know yet. But we will. Someone’ll figure this out, and we’ll have one more victory in our quest to better understand the Universe.

Science! I love this stuff.

Credits: Credit: NASA/SDO; SOHO (ESA & NASA)

Related posts:

- NASA’S SDO captures final moments of a comet streaking across the Sun
- Amazing video of comet on a solar death dive
- Ten Things You Don’t Know About Comets
- The comet and the Coronal Mass Ejection

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.
Read More

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

Lovejoy lives!

By Phil Plait | December 16, 2011 7:00 am

Comet Lovejoy was only discovered in late November, but it’s had quite a ride. It was quickly determined to be a Sun-grazer, the kind of comet that plunges down very close to the Sun in its orbit. The date of this solar close encounter: yesterday!

That’s a shot of it using SOHO, a solar observatory orbiting the Sun. The Sun itself is blocked by a mask, and the white circle represents its outline. The comet is obvious enough! The line through the top of it is not real; that’s called blooming and it happens sometimes when a bright object is seen by a digital detector. The electrons in the chip overflow the pixels and leak into adjacent ones. The comet got very bright as it neared the Sun, almost as bright as Venus! This picture, taken on December 15th at 22:36 UT, was shortly before closest approach: a mere 180,000 km (110,000 miles) from the Sun’s searing surface.

Amazingly, after the comet screamed past the Sun, and to the surprise of many, it survived. A lot of comets don’t make it through such an event, but this one did. Here’s a video of the comet reappearing from behind the Sun, as seen by SDO; watch closely or you’ll miss it!

Nifty. But on the way down it had several interesting things happen to it. Read More

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

The comet and the Coronal Mass Ejection

By Phil Plait | October 4, 2011 9:30 am

On October 1, a bright comet screamed into the Sun, and apparently disintegrated. This happens pretty often, actually, but in this case, just minutes later, the Sun blew out a pretty hefty coronal mass ejection, a huge explosion of magnetic energy that can release billions of tons of material.

Some people have speculated that these two things are related (including times when this has happened in the past). Are they? We have videos of the event from three different satellites, giving us three angles on what happened, providing clues on what really occurred.

To shed some light on this — haha — I made a short video explaining this, including the footage of the comet collision and CME as seen by the three satellites:

[It helps to set the video resolution to 720p to see the details in the satellite views.]

So my guess is that while it’s possible, it’s not probable. CMEs happen all the time, so I’d expect a few to happen around the same time as comets flying past the Sun just by coincidence. We don’t have any physical reason to think they’re related, and when they are examined more closely, the CMEs usually don’t come from a spot near the Sun where the comet traveled. Still, it’s worth looking into, at least to build up a statistical case on way or the other.

The folks at SOHO — the Solar Heliospheric Observatory — have a post up with more info. Also, if you want to see the three satellite videos on their own, here is the SOHO video
the STEREO A video, and the STEREO B video.

Very special thanks to SungrazerComets on Twitter for making the three original satellite animations. That’s a good stream to follow if you want the latest on comets making death dives onto our star. [UPDATE: @SungrazerComets just posted an excellent and thorough article about this topic, too!]

Image credits: NASA, SOHO, STEREO

Related posts:

- Amazing video of comet on a solar death dive
- The Sun blasts out a flare and a huge filament
- Solar storm tracked all the way from the Sun to Earth
- STEREO sees an ethereal solar blast

Summer solstice 2011

By Phil Plait | June 21, 2011 6:30 am

Today, June 21, 2001, at 17:16 UTC (1:16 p.m. Eastern US time), the Sun will reach its peak in its northward travels this year. This moment is the summer solstice — I describe this in detail in an earlier post. Technically, that article is for the winter solstice, but the idea’s the same. Just replace "winter" with "summer" and "December" with "June" and "south" with "north". That should be clear enough. It might be easier just to multiply the entire article by -1. Or stand on your head.

Since for the majority of people on the planet this day marks the start (or more commonly the midpoint) of summer, enjoy the gallery below that shows our nearest star doing what it does best: giving us light, giving us beauty, and sometimes, blowing its top.

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

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