Category: Solar Astronomy

So what’s up with our Sun? Is it going through a depression? It seems as if our closest star is experiencing a surprisingly uneventful couple of years. Solar minimum has supposedly passed and we should be seeing a lot more magnetic activity, and we certainly should be observing lots more sunspots. Space weather forecasts have been putting Solar Cycle 24 as a historically active cycle… but so far, nothing. So what’s the problem? Is it a ticking bomb, waiting to shock us with a huge jump in solar activity, flares and CMEs over a few months? Or could this lack of activity a prelude to a very boring few years, possibly leading the Earth toward another Ice Age?

It’s funny. Just as we begin to get worried that the next solar maximum is going to unleash all sorts of havoc on Earth (i.e. NASA’s 2006 solar storm warning), scientists begin to get concerned as to whether there is going to be a solar maximum at all. In a conference last week at Montana State University, solar physicists discussed the possibility that the Sun could be facing a long period of calm, leading to the concern that there could be another Maunder Minimum. The Maunder Minimum (named after the late 19th Century solar astronomer Edward W. Maunder, who discovered the phenomenon) was a 17th Century, 30-year period when very few sunspots were observed on the disk of the Sun. It is thought by many scientists that this period contributed to what became known as the “Little Ice Age” here on Earth. As the Sun provides Earth with all its energy, during extended periods when the solar output is lower than average, it seems possible a lack of sunspots on the Sun (i.e. low activity) may be linked with periods of cold down here.

“It continues to be dead. That’s a small concern, a very small concern.” – Saku Tsuneta, National Astronomical Observatory of Japan and program manager for the Hinode solar mission.

However, solar physicists are not too worried about this possibility, after all, it’s only been two years since solar minimum. Although activity has been low for the beginning of Cycle 24, sunspots have not been non-existent. In January of this year, a newborn spot was observed, as expected, in high latitude regions. More spots were seen in April. In March, sunspots from the previous solar cycle even made an appearance, putting on an unexpected show of flares and coronal mass ejections (CMEs).

As pointed out by David Hathaway, a solar physicist at NASA’s Marshall Space Flight Center, the fact that sunspots have already been observed in this new cycle means that it is highly unlikely we face anything as extreme as another Maunder Minimum. Hathaway says there is nothing unusual about having a relatively understated solar cycle after several particularly active cycles. Solar Cycle 23 was a very active period for the Sun with a greater than average number of sunspots observed on the solar surface.

It appears there are two different predictions for the activity level of the next solar cycle. On the one hand we have scientists that think this cycle might be below average, and on the other hand we have scientists who believe the next cycle will be the biggest yet. We certainly have a long way to go before we can begin making any accurate solar forecasts…

Source: Space.com

Periodically our sun blasts streams of hot, ionized gas into the solar system. These eruptions, called coronal mass ejections or CMEs pose a potential threat to astronauts or satellites if aimed at Earth. On April 9, the Sun erupted with a CME, and because the eruption was located on the edge or limb of the sun, it was observed in unprecedented detail by a fleet of spacecraft, revealing new features that are predicted by computer models but are otherwise difficult to see, even for specialized sun-watching spacecraft. From these observations, astronomers have been able to create an animation of this spectacular event.

When a CME occurs, usually spacecraft watching the event need to protect themselves from the bright X-ray solar flare associate with a CME. However, since the April 9 CME occurred on the edge or limb of the Sun as viewed from Earth, the solar flare was hidden from view, which allowed spacecraft to take longer exposures and uncover fainter structures than usual.

“Observations like this are very rare,” said Smithsonian astronomer Ed DeLuca.

Using the Smithsonian-developed X-ray Telescope (XRT) aboard the Japanese Hinode sun-watching satellite, astronomers saw a spiral (helical) magnetic structure unwind as it left the Sun during the CME. Such unwinding can release energy as the magnetic field goes from a more twisted to a less twisted configuration, thereby helping to power the eruption.

Hours later, XRT revealed an inflow of material toward a feature that appears as a bright line—actually an object known as a current sheet seen edge-on. A current sheet is a thin, electrified sheet of gas where oppositely directed magnetic field lines annihilate one another in a process known as magnetic reconnection. The extended observations from XRT show that magnetic fields flow in toward the current sheet for many hours after the eruption, progressing first toward the sheet and then down to the sun’s surface.

The astronomers were able to create an animation of the event.

They also determined that the temperature of the current sheet is between 5 and 18 million degrees Fahrenheit, which matches previous measurements higher up in the corona by the Ultraviolet Coronagraph Spectrometer on the SOHO spacecraft.

Astronomers study these explosions in hope of being able to predict them and provide “space weather” forecasts.

Original News Source: Harvard Smithsonian Center for Astrophysics

NASA’s Swift satellite picked up one of the brightest solar flares ever seen — not from our own sun, but a star 16 light-years away. This flare packed the power of thousands of solar flares combined, and a flare of this magnitude from our own sun would have stripped Earth’s atmosphere and sterilized the planet. Astronomers say the flare would have been visible to the naked eye on April 25, 2008 if the star had been easily observable in the night sky at the time. As it was, the flare’s brightness caused Swifts’ Ultraviolet/Optical Telescope to shut down for safety reasons. But Swift was able to study the flare for over 8 hours with its X-ray capabilities.

The Swift satellite normally searches for gamma ray bursts, and is surrounded with detectors that look for bursts of light. The spacecraft then “swiftly” and autonomously re-points itself to the location of the burst. However, this was no gamma ray burst, just a solar flare. But what a solar flare!

The star, EV Lacertae, is a basic red dwarf, the most common type of star in the universe. It shines with only one percent of the Sun’s light, and contains only a third of the Sun’s mass. It’s one of our closest stellar neighbors, but normally is not visible with the naked eye, as it holds a magnitude of -10.

“Here’s a small, cool star that shot off a monster flare. This star has a record of producing flares, but this one takes the cake,” says Rachel Osten, from NASA’s Goddard Space Flight Center. “Flares like this would deplete the atmospheres of life-bearing planets, sterilizing their surfaces.”

Astronomers say EV Lacertae is like an unruly child that throws frequent temper tantrums. It’s a relatively young star at a few hundred million years of age. But it’s a fast rotating star which generates a strong magnetic field, about 100 times as magnetically powerful as the Sun’s field. The energy stored in its magnetic field powers these giant flares.

The flare’s incredible brightness enabled Swift to make detailed measurements in X-ray, as the star remained bright in x-rays for about 8 hours. “This gives us a golden opportunity to study a stellar flare on a second-by-second basis to see how it evolved,” says Stephen Drake of NASA Goddard.

Flares release energy across the electromagnetic spectrum, but the extremely high gas temperatures produced by flares can only be studied with high-energy telescopes like those on Swift. Swift’s wide field and rapid repointing capabilities, designed to study gamma-ray bursts, make it ideal for studying stellar flares. Most other X-ray observatories have studied this star and others like it, but they have to be extremely lucky to catch and study powerful flares due to their much smaller fields of view.

Original News Source: NASA

The solar wind comes in two modes: fast and slow. Solar astronomers have a good idea as to where the fast solar wind comes from: polar coronal holes of open magnetic field lines, blasting solar particles at speeds of over 3 million km/hr. But what about the slow solar wind which fires particles into space at a pedestrian 1.5 million km/hr? We know it comes from the streamer belt above equatorial regions of the Sun, but we have never been able to look lower. But now, with the help of the Hinode observatory, stunning high-resolution images and video have been captured showing solar dynamics previously overlooked. The point at which the Sun ejects slow wind particles into space can now be studied in unparalleled detail to help us understand the dynamics of space weather and solar storms.

The Sun is a complex, magnetic body. Its magnetic field is highly dynamic, varying in activity throughout the 11-year solar cycle. We have just witnessed the Sun entering “Solar Cycle 24” (although some old sunspots from the previous cycle have just been seen) and it will gradually build in energy before reaching “solar maximum” in a few years time (looks like the solar storms will be bigger than 2003’s flare excitement).

This time of relative calm (known as “solar minimum”) allows solar physicists to study the less explosive dynamics in the lower corona (the Sun’s atmosphere), chromosphere and photosphere. It is in this region that magnetic field lines (or magnetic flux) are pushed through the photosphere and the plasma from the solar interior is guided by the magnetic flux high into the corona. These hot and bright arcs of magnetism and superheated plasma are known as coronal loops, the scene of rapid reconnection events, sometimes sparking flares and coronal mass ejections (CMEs). But this time the Hinode science team have observed a steady release of solar plasma, venting from the solar interior around a cluster of bright coronal loop footpoints. The location of this steady release of plasma forms the origin of the slow solar wind.

“It is fantastic to finally be able to pinpoint the source of the solar wind – it has been debated for many years and now we have the final piece of the jigsaw. In the future we want to be able to work out how the wind is transported through the solar system.” – Prof. Louise Harra, University College London, Mullard Space Science Laboratory.

See the Hinode video of the region generating solar wind particles…

These dazzling images were captured by the Extreme Ultraviolet Imaging Spectrometer (EIS) on board the Japanese Hinode solar observatory. The observatory, which orbits the Earth, constantly looking at the Sun, has given us unrivaled observations of the Sun in X-ray and EUV wavelengths. Launched by Japan, the project also has collaborators in the UK and US.

These new discoveries are of vast importance to us. The solar wind carries a stream of highly energetic particles from the Sun and into space. The solar wind bathes the Earth in a radioactive stream, carrying the remnants of the solar magnetic field with it. The magnetic field can interact with the Earth’s magnetic field, allowing solar particles to rain down on our Polar Regions, creating vast light displays: the Aurora. However, these particles are also highly dangerous to any unprotected astronaut or sensitive satellite orbiting our planet. It is of paramount importance that as we venture further and further into space that we forecast the characteristics of the solar wind before it hits us. These new observations will aid our understanding of the conditions at the solar wind source and greatly improve our space weather-predicting ability.

Source: ESA

For you solar observing fans, enjoy the beauty. Over the years both the public and astronomers alike have witnessed the Sun’s volatile and ever-changing atmosphere. Before our eyes huge geysers of hot gas spew into the solar corona at tens of thousands of km per hour. Every few minutes they erupt and reach dynamic proportions. Now a team of scientists have used the Hinode spacecraft to find the origin and progenitor of these fountains – immense magnetic structures that thread through the solar atmosphere.

Today at the Royal Astronomical Society National Astronomy Meeting in Belfast (NAM 2008), team leader Dr. Michelle Murray from the Mullard Space Science Laboratory (MSSL, University College London) presented the latest results from Hinode spacecraft combined with computer emulated solar conditions. Since its launch in October 2006, scientists have been using Hinode to examine the solar atmosphere in extraordinary detail. One of it’s premier instruments is the Extreme Ultraviolet Imaging Spectrometer. The EIS generates images of the Sun and gives information on the speed of the moving gases.

At the core of the solar magnetic field, immense jets of hot gas are forced to the surface through increases in pressure. Just like an earthly geyser, when the pressure releases the gases fall back towards the Sun’s surface. But what causes the pressure? Unlike the volcanic activity that drives the terrestrial phenomena, solar fountains are caused by rearrangements of the Sun’s magnetic field, a continual process that results in looping cycles of increasing and decreasing pressure.

“EIS has observed the Sun’s fountains in unprecedented detail and it has enabled us to narrow down the fountains’ origins for the first time”, comments team member and MSSL postgraduate student Deb Baker. “We have also been able to find what drives the fountains by using computer experiments to replicate solar conditions.”

The sun-observing Hinode satellite is now in a sun-synchronous orbit, which allows it to observe the sun for uninterrupted periods lasting months at a time. Using a combination of optical, EUV and X-ray instrumentation Hinode will study the interaction between the Sun’s magnetic field and its corona to increase our understanding of the causes of solar variability.

“The computer experiments demonstrate that when a new section of magnetic field pushes through the solar surface it generates a continual cycle of fountains”, explains Dr. Murray, “but new magnetic fields are constantly emerging across the whole of the solar surface and so our results can explain a whole multitude of fountains that have been observed with Hinode.”

A solar tsunami blasted its way through the sun’s lower atmosphere on May, 19 2007, and the action was captured by the twin STEREO spacecraft. Solar tsunamis are launched by huge explosions near the Sun’s atmosphere, called coronal mass ejections (CMEs). Although solar tsunamis share much in common with tsunamis on Earth, the solar version can travel at over a million kilometers per hour. Last year’s tsunami blasted and rolled for about 35 minutes, reaching peak speeds around 20 minutes after the initial flare. The observations were made by a team from Trinity College, Dublin.

“The energy released in these explosions is phenomenal; about two billion times the annual world energy consumption in just a fraction of a second. In half an hour, we saw the tsunami cover almost the full disc of the Sun, nearly a million kilometers away from the epicenter,” said David Long, a member of the team that made the observations.

STEREO’s Extreme Ultraviolet Imager (EUVI) instruments monitor the Sun at four wavelengths which correspond to temperatures ranging between 60,000 and 2 million degrees Celsius. At the lowest of these temperatures, scientists can see structures in the chromosphere, a thin layer of the solar atmosphere that lies just above the Sun’s visible surface. At temperatures between 1 and 2 million degrees Celsius, scientist can monitor features at varying levels in the solar corona.

The SOHO spacecraft, which was launched in 1995, also monitors the Sun at these wavelengths but only took images four times per day, giving scientists rare snapshots of these tsunamis. STEREO’s EUVI instruments take an image every few minutes to create a series, making it possible for scientists to track how the wave spreads over time.

Click here for a Quicktime animation of the event.

This is the first time that a tsunami has been observed at all four wavelengths, which enabled the team to see how the wave moved through the different layers of the solar atmosphere.

“To our surprise, the tsunami seems to move with similar speed and acceleration through all the layers. As the chromosphere is much denser than the corona, we’d expect the pulse there to drag. It’s a real puzzle,” said Dr. Peter Gallagher, another member of the team.

To complicate matters, the interval between images is not the same for all four cameras. At the time of the tsunami, the cameras monitoring radiation at 1 million degrees Celsius were set to take an image every 2.5 minutes. They recorded much higher speeds and accelerations for the wave than the other cameras, which were on 10 or 20 minute cycles. By taking a sample of one image in four, the data from these cameras matched the lower values observed in the other layers.

“We’ve thought for some time that the tsunamis might be caused by magnetic shockwaves but, in previous snapshots, the waves appeared to be travelling too slowly. However, we’ve seen from this set of observations that if the time interval between images is too long, it’s easy to underestimate the speed that the waves are moving. With a few more rapid-sequence observations of solar tsunamis, we should finally be able to identify the cause of these waves,” said Gallagher.

The discovery will be presented by David Long at the RAS National Astronomy Meeting in Belfast on Wednesday April 2, 2008.

For more information and animations, see Trinity College’s pageabout the solar tsunami.

Original News Source: RAS press release