Sun sunspots show up during the recent annular eclipse. Credit: Shehal Joseph and Romayne Anthony
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Astrophotographers capturing the recent annular solar eclipse on January 15, 2010 got an added bonus: upon closer inspection, they found sunspot 1040 also showed up on their images, too. “We didn’t mean to catch sunspots in our Jaffna Eclipse expedition, nor did we plan to,” said Prasanna Deshapriya, one of the members of the Eclipse Hunt 2010 crew, featured in our eclipse photo and video collection. “But surprisingly this is what really happened.”
SOHO image of sunspot 1040 on January 15, 2010. credit: SOHO/MDI
The rather big sunspot 1040, which was also captured by the SOHO spacecraft on Jan. 15 has just disappeared over the sun’s western limb, currently leaving the visible disk of the sun blank once again in this uncharacteristically long solar minimum. But our old friend, sunspot 1039 should be showing up soon, as the sun rotates around. We know it is still there, because the STEREO spacecraft can show us what is going on the sun’s far side. Sunspot 1039 should emerge for direct viewing from Earth within the next 48 hours. Spaceweather.com encourages those amateur astronomers with solar telescopes to monitor the Sun’s east limb for developments.
STEREO B captures the largest solar flare in two years. Click for larger movie.
Additionally on Jan. 19th at 1340 UT, STEREO-B recorded the strongest solar flare in almost two years. Click the image to see the action on an ultraviolet movie of the blast. The M2-class eruption came from sunspot 1039, so that sunspot is likely still very active.
Spaceweather.com said that considering the sunspot was not even visible from Earth at the time of the eruption, the flare was probably much stronger than its M2 classification would suggest. This active region has produced at least three significant eruptions since Jan. 17th and it shows no signs of cooling off.
The current solar cycle (24) has been pretty boring, but a new sunspot — 1035 — is growing rapidly and now is seven times wider than Earth. Solar astronomers are predicting it could grow to be the largest sunspot of the year. There’s not been a lot of competition for the biggest sunspot, though: for 259 days (or 74%) of 2009, the sun has been spotless. But maybe the (solar) tide is turning. There’s been other action recently besides the new sunspot. A long-duration C4-class solar flare erupted this morning at 0120 UT from around the sunspot, which hurled a coronal mass ejection (CME) towards Earth. (See below for image of the CME that blasted off the sun on Dec. 14) Observers at high-latitude could see some aurora action when the CME arrives on or about Dec. 18th. Keep cheering; maybe the sun will come out of its doldrums.
CME on Dec. 14, 2009. Credit: NASA, SoHO
Remember, don’t look at the Sun directly to try and see the sunspot. NASA has a great site that gives real-time data and updated images of the Sun from SoHO (Solar and Heliospheric Observatory.) Or check out Spaceweather.com, which also provides updates. And if you have a safe way of observing and imaging the sunspot, feel free to post images here, or send to Nancy.
Artists concept of Chi Cygni Credit: ESO/L. Calçada
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When our Sun begins to die, it will become a red giant as it runs out of hydrogen fuel at its core. Astronomers have a pretty good idea of what will transpire: the sun will swell to a size so large that it will swallow every planet out to Mars in our solar system. Don’t worry, though, this won’t happen for another 5 billion years. But now, astronomers have been able to watch in detail the death of a sun-like star about 550 light-years from Earth to get a better grasp on what the end might be for our Sun. The star, Chi Cygni, has swollen in size, and is now writhing in its death throes. The star has begun to pulse dramatically in and out, beating like a giant heart. New close-up photos of the surface of this distant star show its throbbing motions in unprecedented detail.
Using interferometry to image the star's surface at four separate times, astronomers found that the star grows to a diameter of 480 million miles - large enough to engulf the asteroid belt - before shrinking to a minimum diameter of 300 million miles. Chi Cygni also shows significant hotspots near minimum radius. Credit: Sylvestre Lacour, Observatoire de Paris
“This work opens a window onto the fate of our Sun five billion years from now, when it will near the end of its life,” said Sylvestre Lacour of the Observatoire de Paris, who led a team of astronomers studying Chi Cygni.
The scientists compared the star to a car running out of gas. The “engine” begins to sputter and pulse. On Chi Cygni, the sputterings show up as a brightening and dimming, caused by the star’s contraction and expansion.
For the first time, astronomers have photographed these dramatic changes in detail.
“We have essentially created an animation of a pulsating star using real images,” stated Lacour. “Our observations show that the pulsation is not only radial, but comes with inhomogeneities, like the giant hotspot that appeared at minimum radius.”
Stars at this life stage are known as Mira variables. As it pulses, the star is puffing off its outer layers, which in a few hundred thousand years will create a beautifully gleaming planetary nebula.
Chi Cygni pulses once every 408 days. At its smallest diameter of 300 million miles, it becomes mottled with brilliant spots as massive plumes of hot plasma roil its surface, like the granules seen on our Sun’s surface, but much larger. As it expands, Chi Cygni cools and dims, growing to a diameter of 480 million miles – large enough to engulf and cook our solar system’s asteroid belt.
Imaging variable stars is an extremely difficult task. First, Mira variables hide within a compact and dense shell of dust and molecules. To study the stellar surface within the shell, astronomers need to observe the stars in infrared light, which allows them to see through the shell of molecules and dust, like X-rays enable physicians to see bones within the human body.
Secondly, these stars are very far away, and thus appear very small. Even though they are huge compared to the Sun, the distance makes them appear no larger than a small house on the moon as seen from Earth. Traditional telescopes lack the proper resolution. Consequently, the team turned to a technique called interferometry, which involves combining the light coming from several telescopes to yield resolution equivalent to a telescope as large as the distance between them.
They used the Smithsonian Astrophysical Observatory’s Infrared Optical Telescope Array, or IOTA, which was located at Whipple Observatory on Mount Hopkins, Arizona.
“IOTA offered unique capabilities,” said co-author Marc Lacasse of the Harvard-Smithsonian Center for Astrophysics (CfA). “It allowed us to see details in the images which are about 15 times smaller than can be resolved in images from the Hubble Space Telescope.”
The team also acknowledged the usefulness of the many observations contributed annually by amateur astronomers worldwide, which were provided by the American Association of Variable Star Observers (AAVSO).
In the forthcoming decade, the prospect of ultra-sharp imaging enabled by interferometry excites astronomers. Objects that, until now, appeared point-like are progressively revealing their true nature. Stellar surfaces, black hole accretion disks, and planet forming regions surrounding newborn stars all used to be understood primarily through models. Interferometry promises to reveal their true identities and, with them, some surprises.
The new observations of Chi Cygni are reported in the December 10 issue of The Astrophysical Journal.
A sun dog is an atmospheric phenomenon where you can see additional bright patches in the sky on either side of the Sun. Sometimes you just see bright spots, and sometimes you can actually see an arc or even a halo around the Sun. These are all related to sun dogs, and have to do with very specific atmospheric conditions. If you’ve ever seen a sun dog, you were very lucky, and they only occur rarely.
Sun dogs occur because of sunlight refracting through ice crystals in the atmosphere. The crystals cause the sunlight to bend at a minimum angle of 22°. All of the crystals are refracting the Sun’s rays, but we only see the ones which are bent towards our eyes. Because this is the minimum, the light looks more concentrated starting at 22° away from the Sun; about 40 times the size of the Sun in the sky. At this 22° point you can get arcs, a halo, or just bright spots in the sky.
They can occur at any time of the year and from any place on Earth; although, they’re easiest to see when the Sun is lower on the horizon. As the Sun rises, the sun dog can actually drift away from the 22° point. Eventually the Sun gets so high that the sun dog disappears entirely.
There are no set colors with sun dogs. The light from the Sun is being refracted equally by the ice crystals and so we don’t see the colors broken up as we do with a rainbow.
We’ve written several articles about the Sun for Universe Today. Here’s an article about a ring around the Sun, and here’s an article about rings around the Moon.
Green Flash in Santa Cruz, California. Image credit: Mila Zinkova
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Have you ever heard of a green flash sunset? You might think it’s a myth, but this is a real phenomenon that you can see if the conditions are just right. If you’re watching the Sun dip down on the horizon you might see a green dot appear just above the Sun for just a second. That’s a green flash sunset, and if you saw one, you’re a very lucky person.
Green flashes can occur at sunrise or sunset, and to see one, you need to have an unobstructed view to the horizon. They occur because the light from the Sun is refracted – or bent – as it passes through the Earth’s atmosphere, following the curvature of the Earth. Higher frequency light (bluer light) is bent more than lower frequency light. This is happening all the time, but we’re seeing all the colors of the light spectrum at the same time. But when the Sun is right at the horizon, the redder hues of the color spectrum are blocked by the horizon of the Earth, while the higher frequency wavelengths are still following the curve of the Earth. While the redder light is blocked, the green and blue light is still visible, so we see the green flash.
There are actually a few different kinds of green flashes that can occur. The most common example is an inferior-mirage flash, where a dot of green light appears on top of the Sun just as it’s gone below the horizon. But you can also get a situation where a portion of the Sun’s upper edge turns slightly green, or even a green beam of light appears above the Sun.
We’ve written a few articles about sunsets for Universe Today. Here’s an article about green flashes, and here are some cool pictures of sunsets seen from other worlds.
Plasma on the surface of the Sun. Image credit: Hinode
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The Sun may look like just a mass of incandescent gas (plasma, really), but it’s actually broken up into layers. The chromosphere is relatively thin region of the Sun that’s just above the photosphere.
The photosphere is the region of the Sun that we see. It measures an average temperature of almost 5,800 kelvin and produces the visible radiation. This is the point where photons generated inside the Sun can finally leap out into space. The chromosphere measures just 2,000 km, and it’s just outside the photosphere.
Even though it’s very thin, the chromosphere changes dramatically in density, from the top down to the photosphere, the density of the chromosphere increases by a factor of 5 million. The upper boundary of the chromosphere is the called the solar transition region, above which is known as the corona.
One surprising mystery is that the chromosphere is actually hotter than the photosphere. While the photosphere hovers around 5,800 kelvin, the temperature of the chromosphere varies between 4,500 K and 20,000 K. Even though it’s more distant from the center of the Sun, the chromosphere is hotter than the photosphere. Astronomers think turbulence in the Sun’s atmosphere might somehow cause this extra heating.
The chromosphere is difficult to see without special equipment because the light from the much brighter photosphere washes it out. It has a reddish color, but you can only really see it during a total solar eclipse.
One of the recognizable features of the chromosphere are spicules. These are fingers of gas that kind of look like grass growing on the surface of the Sun. These can rise up in the chromosphere and then disappear again within 10 minutes.
The Pluto system seen from the surface of Hydra. Credit: NASA
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How far away is Pluto from the Sun? Pluto’s average distance from the Sun is 5.9 billion km or 3.7 billion miles.
But Pluto actually follows an elliptical orbit around the Sun. Sometimes it’s much closer to the Sun, and other times it’s further away. At its closest point, Pluto measures only 4.4 billion km from the Sun. This is close enough that a thin layer of frost evaporates from its surface, becoming a thin atmosphere around the planet. And then as it continues its journey around the Sun, Pluto gets colder again and this atmosphere refreezes onto the planet. It continues to travel out to a distance of 7.4 billion km from the Sun.
Astronomers use another method of measuring distances in the Solar System called the astronomical unit. 1 astronomical unit or AU is the average distance from the Earth to the Sun; approximately 150 million km. So we can use this to describe Pluto’s distance from the Sun. At its closest point, Pluto measures 29.7 AU. And then at its furthest point, Pluto is 49.3 AU.
Artist’s impression of a baby star still surrounded by a protoplanetary disc in which planets are forming. Credit: ESO
For decades, astronomers have known our Sun contains a low amount of lithium, while other solar-like stars actually have more. But they didn’t know why. By looking at stars similar to the Sun to study this anomaly, scientists have now discovered of a trend: the majority of stars hosting planets possess less than 1% of the amount of lithium shown by most of the other stars. “The explanation of this 60 year-long puzzle is for us rather simple,” said Garik Israelian, lead author on a paper appearing in this week’s edition of Nature. “The Sun lacks lithium because it has planets.”
This finding sheds light not only on the lack of lithium in our star, but also provides astronomers with a very efficient way of finding stars with planetary systems.
Isrealian and his team took a census of 500 stars, 70 of which are known to host planets, and in particular looked at Sun-like stars, almost a quarter of the whole sample. Using ESO’s HARPS spectrograph, a team of astronomers has found that Sun-like stars that host planets have destroyed their lithium much more efficiently than “planet-free” stars.
“For almost 10 years we have tried to find out what distinguishes stars with planetary systems from their barren cousins,” Israelian said. “We now have found that the amount of lithium in Sun-like stars depends on whether or not they have planets.”
These stars have been “very efficient at destroying the lithium they inherited at birth,” said team member Nuno Santos. “Using our unique, large sample, we can also prove that the reason for this lithium reduction is not related to any other property of the star, such as its age.”
Unlike most other elements lighter than iron, the light nuclei of lithium, beryllium and boron are not produced in significant amounts in stars. Instead, it is thought that lithium, composed of just three protons and four neutrons, was mainly produced just after the Big Bang, 13.7 billion years ago. Most stars will thus have the same amount of lithium, unless this element has been destroyed inside the star.
This result also provides the astronomers with a new, cost-effective way to search for planetary systems: by checking the amount of lithium present in a star astronomers can decide which stars are worthy of further significant observing efforts.
Now that a link between the presence of planets and curiously low levels of lithium has been established, the physical mechanism behind it has to be investigated. “There are several ways in which a planet can disturb the internal motions of matter in its host star, thereby rearrange the distribution of the various chemical elements and possibly cause the destruction of lithium,” said co-author Michael Mayor. ” It is now up to the theoreticians to figure out which one is the most likely to happen.”
SUNRISE enables tiny magnetic fields on the surface of the Sun to be measured at a level of detail never before achieved. Credit: Image: MPS/IMAX consortium
Exploring the Sun via helium balloon almost sounds like an adventure for an animated movie, but the SUNRISE balloon-borne telescope has captured data and images that show the complex interplay on the solar surface to a level of detail never before achieved. As in the video above, SUNRISE shows our local star to be a bubbling, boiling mass where packages of gas rise and sink, lending the sun its grainy surface structure. Dark spots appear and disappear, clouds of matter dart up – and behind the whole thing are the magnetic fields, the engines of it all.
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“Thanks to its excellent optical quality, the SUFI instrument was able to depict the very small magnetic structures with high intensity contrast, while the IMaX instrument simultaneously recorded the magnetic field and the flow velocity of the hot gas in these structures and their environment,” said Dr. Achim Gandorfer, project scientist for SUNRISE at the Max Planck Institute for Solar System Research.
Previously, the observed physical processes could only be simulated with complex computer models.
“Thanks to SUNRISE, these models can now be placed on a solid experimental basis,” said Manfred Schüssler, co-founder of the mission.
SUNRISE is the largest solar telescope ever to have left Earth. It was launched from the ESRANGE Space Centre in Kiruna, northern Sweden, on June 8, 2009. The total equipment weighed in at more than six tons on launch. Carried by a gigantic helium balloon with a capacity of a million cubic meters and a diameter of around 130 meters, SUNRISE reached a cruising altitude of 37 kilometers above the Earth’s surface.
In the stratosphere, observational conditions are similar to those in outer space. The images are no longer affected by air turbulence, and the camera can also zoom in on the Sun in ultraviolet light, which would otherwise be absorbed by the ozone layer. After making its observations, SUNRISE separated from the balloon, and parachuted safely down to Earth on June 14th, landing on Somerset Island, a large island in Canada’s Nunavut Territory. Grainy sun: the images show the so-called granulation in four different wavelengths in near ultraviolet light. The image section depicts 1/20,000 of the entire surface. The smallest recognisable structures have an angular resolution equal to that of looking at a coin from a distance of 100 kilometres. The light structures are the foundational elements of the magnetic fields. Credit: Image: MPI for Solar System Research
The work of analyzing the total of 1.8 terabytes of observation data recorded by the telescope during its five-day flight has only just begun. Yet the first findings already give a promising indication that the mission will bring our understanding of the Sun and its activity a great leap forward. What is particularly interesting is the connection between the strength of the magnetic field and the brightness of tiny magnetic structures. Since the magnetic field varies in an eleven-year cycle of activity, the increased presence of these foundational elements brings a rise in overall solar brightness – resulting in greater heat input to the Earth.
The variations in solar radiation are particularly pronounced in ultraviolet light. This light does not reach the surface of the Earth; the ozone layer absorbs and is warmed by it. During its flight through the stratosphere, SUNRISE carried out the first ever study of the bright magnetic structures on the solar surface in this important spectral range with a wavelength of between 200 and 400 nanometers (millionths of a millimeter).
SUNRISE is a collaborative project between the Max Planck Institute for Solar System Research in Katlenburg-Lindau, with partners in Germany, Spain and the USA.
Plasma on the surface of the Sun. Image credit: Hinode
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The Sun is the hottest place in the Solar System. The surface of the Sun is a mere 5,800 Kelvin, but down at the core of the Sun, the temperatures reach 15 million Kelvin. What’s going on, why is the Sun hot?
The Sun is just a big plasma ball of hydrogen, held together by the mutual gravity of all its mass. This enormous mass pulls inward, trying to compress the Sun down. It’s the same reason why the Earth and the rest of the planets are spheres. As the pull of gravity compresses the gas inside the Sun together, it increases the temperature and pressure in the core.
If you could travel down into the Sun, you’d reach a point where the pressure and temperature are enough that nuclear fusion is able to take place. This is the process where protons are merged together into atoms of helium. It can only happen in hot temperatures, and under incredible pressures. But the process of fusion gives off more energy than it uses. So once it gets going, each fusion reaction gives off gamma radiation. It’s the radiation pressure of this light created in the core of the Sun that actually stops it from compressing any more.
The Sun is actually in perfect balance. Gravity is trying to squeeze it together into a little ball, but this creates the right conditions for fusion. The fusion releases radiation, and it’s this radiation that pushes back against the gravity, keeping the Sun as a sphere.
