Sunspots are one way we can track the activity of the Sun. There have been fewer sunspots than usual in recent years, and that may point toward an historic solar minimum. 

Sunspots are dark patches that occasionally appear on the surface of the Sun. They aren’t actually dark. If you could see a sunspot by itself it would appear bright red, but since sunspots are about a quarter as bright as the rest of the Sun, they appear as dark regions. Since the early 1600s astronomers have counted the number of sunspots over the years, and we’ve noticed a few patterns. One is that sunspot counts vary between maximum and minimum over an 11-year period. There are other patterns as well, such as the Gleisberg Cycle, which lasts 80 – 90 years.

Directly recorded sunspot counts over the years. Credit: Robert A. Rohde (CC BY-SA 3.0)

There are times when the pattern seems to break down, and the Sun can enter into an extended period of little sunspot activity. The most famous is the Maunder minimum of the 1600s. While we don’t have direct sunspot counts before the early 1600s, we can look at the levels of carbon-14 as measured from tree rings. Since carbon-14 levels have a good correlation to sunspot counts, we can get a handle on a much longer history of sunspots. It turns out there have been other periods of minimum activity, such as the Wolf minimum of the 1300s. In general, the sunspot activity of the Sun in recent centuries is somewhat higher than most, except for a period during the middle ages known as the Medieval maximum.

For the past couple of cycles the sunspot maximums have been lower than usual. The pattern is similar to the early stages of the Dalton minimum in the early 1800s, which has raised the question of whether we are entering a period of reduced sunspot activity. This may also have some effect on global temperatures. The Dalton minimum saw a brief period of colder temperatures, and the Maunder minimum was marked by the “little ice age” where Europe and North America experienced a colder period. It should be stressed that connections between sunspot activity and global temperatures is still not clear. The Dalton cold period for example, saw the explosion of Mount Tambora, which would also contribute to cooler temperatures.

What is clear is that periods of minimal sunspot activity are notoriously difficult to predict. While the pattern of the past few cycles has similarities with the early Dalton minimum, it could also be a small fluke before a return to cycles as normal.

The post Year Of The Quiet Sun appeared first on One Universe at a Time.

NASA’s Solar Dynamics Observatory has been observing the Sun for five years. It’s goal is to study the dynamic variations of the Sun and how they affect our planet. It’s gathered 2.6 petabytes of information, and its data is used for a range of scientific work, from helioseismology and studies of the corona to solar flares and sunspots. It’s also gathered some stunning visuals showing the complex dance of our closest star. Some of the visuals from year five are presented in this wonderful video.

Throughout the video you can see prominences that burst out from the solar surface and wisps of plasma flowing along magnetic field lines. There are filaments looking like cracks in the Sun, and bubbling granules as material from the warmer interior churns toward the Sun’s surface. You can watch coronal mass ejections, and see how the limb of the Sun appears cooler and dimmer. You can even see a transit of Venus.

Often in astronomy, it is the brief moments of fame that get the greatest attention. The landing on a comet, or on Titan. The mission to Ceres, or the upcoming Pluto flyby. These missions deserve the recognition they get, but there are also missions such as the SDO, which quietly gather data, year after year. Though not nearly as sexy, they are just as important as the missions that dance in the Sun.

The post Dancing in the Sun appeared first on One Universe at a Time.

Recently there’s been a flurry of articles about an increase in solar activity, including rumors that Edward Snowden had revealed the NSA knows of a solar flare “killshot” set to cause a global famine that will kill millions. The rumor has since been traced back to a satirical website, but that didn’t prevent the story from being repeated across the internet. The story has flared up again in the past few days on new that NASA has reported the Sun has emitted a coronal mass ejection (CME) in the direction of Earth.

Are we really doomed? No.

A coronal mass ejection occurs when a burst of solar material (mostly ionized hydrogen) is blasted off the Sun. These happen fairly regularly when the Sun is in an active period. If it occurs in the direction of Earth, the ionized material interacts with the Earth’s magnetic field, and are driven toward the polar regions where they and produce northern (and southern) lights. Mass ejections can also interfere with satellites, but we have ways to minimize their effect. So the announcement of a CME is not a huge deal.

Intense solar activity can have larger effects on us, such as causing power outages. In 1989 a large solar flare triggered a regional blackout in Quebec. So when solar flares hit the news there are the range of websites predicting the dreaded “big one”. Theses sites often reference the “Carrington Event” of 1859, which was so intense it produced northern lights as far south as the Caribbean. It also induced currents in telegraph lines. The storm induced enough current in the lines that messages could be sent across them even while the lines were disconnected from their power supplies.

If such an event occurred today, it would likely cause massive blackouts worldwide. It could cause trillions of dollars in damage, and would take several years to fully recover. It would be a massive disruption, but it wouldn’t be the end of civilization. Fortunately, studies of ice cores indicate that solar storms such as the Carrington Event only occur about once every 500 years, and there is no indication that such an event is likely to happen any time soon.

Of course the up-side of solar activity is that we have the opportunity to observe it. Take for example the awesome image above of a solar prominence. You can see the ionized material follow the curved magnetic fields near the Sun’s surface. Just to give you a sense of scale, this particular image is a bit wider than the distance from the Earth to the Moon.

So don’t listen to the rumors. Just sit back, relax, and enjoy the show.

HT to Emmanuel Conseil for sharing this image on Google+, and Nikkey Bozz for suggesting the topic.

The post Oh God, Oh God, We’re All Gonna Die appeared first on One Universe at a Time.

Growing up I was a bit of a risk taker. Along with a few of my friends, I occasionally did things that (while very cool) were in retrospect notoriously dangerous. Occasionally my Mom found out about these activities, which worried her to no end. As she put it, “You could have died!” This is absolutely true. Some of the stunts we pulled could have ended in serious injury or death. It is also true that my friends and I survived childhood largely unscathed. The reason I bring this up is because recently there has been a flurry of stories about solar activity in 2012, and the headlines are much the same “You could have died!”

There is some truth to this. In 2012 there was a very large coronal mass ejection emitted by the Sun. A coronal mass ejection (CME) occurs when a burst of solar material (mostly ionized hydrogen) is blasted off the Sun.  These happen fairly regularly when the Sun is in an active period.  If it occurs in the direction of Earth, the ionized material interacts with the Earth’s magnetic field, and are driven toward the polar regions where they and produce northern (and southern) lights.

This type of solar activity can have large effects on us, such as causing power outages.  In 1989 a large solar flare triggered a regional blackout in Quebec.  There was also a very large  CME that led to the “Carrington Event” of 1859, which was so intense it produced northern lights as far south as the Caribbean.  It also induced currents in telegraph lines.  The storm induced enough current in the lines that messages could be sent across them even while the lines were disconnected from their power supplies. If such an event occurred today, it would likely cause massive blackouts worldwide.  It could cause trillions of dollars in damage, and would take several years to fully recover.  Such a large disruption of infrastructure would almost certainly lead to some deaths.

If the 2012 CME had occurred a week earlier, then it would have produced a Carrington-scale event. People would have died, and among those could have been you or me. It is also true that in 2004 the 4 km wide asteroid 4179 Toutatis came within 4 lunar distances of colliding with Earth.  If it had a slightly different orbit, we could have died.

But we didn’t.

Therein lies the challenge of reporting events like this. On the one hand, our modern technological infrastructure does face a very real risk from solar activity. Studies of ice cores indicate that solar storms such as the Carrington Event only occur about once every 500 years, so it isn’t very common, but the risk isn’t zero either. It is also very clear that our infrastructure is not prepared for a Carrington event, and should be. On the other hand, we don’t want to overplay the risk either.  Having this CME miss us by a week is about the same as having a 4 km rock miss us by a few lunar distances.  In the past, without detailed astronomical studies, we wouldn’t have known about them at all.

If we can use this information to be better prepared in the future, then that is to our advantage. But if we simply use stories to scare people with doomsday scenarios, then we’re better off not knowing about them.

The post You Could Have Died! appeared first on One Universe at a Time.

We generally think of the Sun as a steady constant, but it’s actually quite variable.  The Sun’s magnetic field varies over time, which means the activity of the Sun varies.  The earliest observation of this cycle was seen in sunspots.  While sunspots were observed throughout history, in the early 1600s astronomers began making regular observations of sunspots, and soon discovered an 11-year cycle of high and low sunspot activity.  Over time similar variations in solar flare activity and brightness.  Thus the Sun cycles through active and quiet periods.
In the early 1800s Joseph von Fraunhofer discovered that sunlight was not a continuous range of colors, but rather had gaps at certain wavelengths.  These gaps are now called Fraunhofer lines, and we now know they are cause by the Sun’s atmosphere absorbing certain wavelengths of light the Sun produces.  The specific wavelengths that are absorbed depends on the type of atoms and molecules which are in the Sun’s atmosphere.  We see the same effect in the light of other stars, which is how we can determine the types of elements a particular star has.

Two of these absorption lines in the ultraviolet are known as the H and K lines.  They are due to the presence of calcium in the Sun’s atmosphere.  These particular lines are affected by magnetic activity, so when the Sun is active you can actually get H and K emission lines.  The greater the magnetic activity, the stronger these lines are.  This is useful because we can observe these spectral lines in other stars.

Directly measuring the magnetic activity of other stars is very difficult, since we can’t observe most stars as a disk.  That means we can’t observe sunspots on stars other than our Sun (starspots).  But since we can observe the H and K lines of stars, and these correlate to magnetic activity, we can observe these lines over time to study the activity cycles of other stars.

In 1966, Mount Wilson Observatory began a project to observe the H-K lines of about a hundred local stars.  The project has been ongoing continuously, and now monitors about 400 stars.  This means we have long-term observations of the activity cycles of hundreds of stars.  You can see examples of these in the figure below.  Some stars have short activity cycles (less than 3 years), while others have cycles of more than 20 years.  A few stars seem to be in a long inactive period, similar to the Maunder minimum our Sun had in the late 1600s.

Activity cycles of several stars. Credit: Mount Wilson Observatory

We now have other ways to observe stellar activity cycles.  For example, the Sun’s active periods also produce more x-rays.  X-ray telescopes such as XMM-Newton have observed similar variations in sun-like stars, and these cycles correlate to the H-K cycles of the stars.

Observations such as these continue to confirm that our Sun is just a star like many others throughout the galaxies.  There are billions of stars in the universe, but we think one of them is special, simply because it’s ours.

The post Cycle of Stars appeared first on One Universe at a Time.