The Sun has a lot of rhythm and goes through different cycles of activity. The most well-known cycle might be the Schwabe cycle, which has an 11-year cadence. But what about cycles with much longer time scales? How can scientists understand them?
As it turns out, the Sun has left some hidden clues in tree rings.
The surface of the Sun is a turbulent dance of gravity, plasma, and magnetic fields. Much like the weather on Earth, its behavior can seem unpredictable, but there are patterns to be found when you look closely.
Starting in late 2019, Betelgeuse began drawing a lot of attention after it mysteriously started dimming, only to brighten again a few months later. For a variable star like Betelgeuse, periodic dimming and brightening are normal, but the extent of its fluctuation led to all sorts of theories as to what might be causing it. Similar to Tabby’s Star in 2015, astronomers offered up the usual suspects (minus the alien megastructure theory!)
Whereas some thought that the dimming was a prelude to the star becoming a Type II supernova, others suggested that dust clouds, enormous sunspots, or ejected clouds of gas were the culprit. In any case, the “Great Dimming of Betelgeuse” has motivated an international team of astronomers to propose that a “Betelgeuse Scope” be created that cant monitor the star constantly.
The sun goes through a regular 11-year cycle, swinging between periods of dormancy and periods of activity. Scientists from NASA and NOAA have just announced that the sun has just passed its minimum, and will be ramping up in activity over the next few years, meaning that we have entered a new round of the never-ending solar cycle.
I think we all do sometimes. It’s easy to take for granted. The Sun is that glowing thing that rises in the morning and sets in the evening that we don’t generally pay attention to as we go about our day. However, there are these rare moments when we’re reminded that the Sun is truly a STAR – a titanic living sphere of hydrogen smashing plasma a million times the volume of Earth. One of those rare moments for me was standing in the shadow of the 2017 solar eclipse. We had driven down from Vancouver to Madras, Oregon to watch this astronomical freak of nature. A moon hundreds of times smaller than the Sun, but hundreds of times closer, covers the face of the Sun for the majesty of a STAR to be revealed; the fiery maelstrom of the Sun’s atmosphere visible to the naked eye.
Sunspots are common on our Sun. These darker patches are cooler than their surroundings, and they’re caused by spikes in magnetic flux that inhibit convection. Without convection, those areas cool and darken.
Lots of other stars have sunspots, too. But Red Giants (RGs) don’t. Or so astronomers thought.
A new study shows that some RGs do have spots, and that they rotate faster than thought.
To the naked eye, the Sun puts out energy in a continual, steady state, unchanged through human history. (Don’t look at the sun with your naked eye!) But telescopes tuned to different parts of the electromagnetic spectrum reveal the Sun’s true nature: A shifting, dynamic ball of plasma with a turbulent life. And that dynamic, magnetic turbulence creates space weather.
Space weather is mostly invisible to us, but the part we can see is one of nature’s most stunning displays, the auroras. The aurora’s are triggered when energetic material from the Sun slams into the Earth’s magnetic field. The result is the shimmering, shifting bands of color seen at northern and southern latitudes, also known as the northern and southern lights.
There are two things that can cause auroras, but both start with the Sun. The first involves solar flares. Highly-active regions on the Sun’s surface produce more solar flares, which are sudden, localized increase in the Sun’s brightness. Often, but not always, a solar flare is coupled with a coronal mass ejection (CME).
A coronal mass ejection is a discharge of matter and electromagnetic radiation into space. This magnetized plasma is mostly protons and electrons. The CME ejection often just disperses into space, but not always. If it’s aimed in the direction of the Earth, chances are we get increased auroral activity.
The second cause of auroras are coronal holes on the Sun’s surface. A coronal hole is a region on the surface of the Sun that is cooler and less dense than surrounding areas. Coronal holes are the source of fast-moving streams of material from the Sun.
Whether it’s from an active region on the Sun full of solar flares, or whether it’s from a coronal hole, the result is the same. When the discharge from the Sun strikes the charged particles in our own magnetosphere with enough force, both can be forced into our upper atmosphere. As they reach the atmosphere, they give up their energy. This causes constituents in our atmosphere to emit light. Anyone who has witnessed an aurora knows just how striking that light can be. The shifting and shimmering patterns of light are mesmerizing.
The auroras occur in a region called the auroral oval, which is biased towards the night side of the Earth. This oval is expanded by stronger solar emissions. So when we watch the surface of the Sun for increased activity, we can often predict brighter auroras which will be more visible in southern latitudes, due to the expansion of the auroral oval.
Something happening on the surface of the Sun in the last couple days could signal increased auroras on Earth, tonight and tomorrow (March 28th, 29th). A feature called a trans-equatorial coronal hole is facing Earth, which could mean that a strong solar wind is about to hit us. If it does, look north or south at night, depending on where your live, to see the auroras.
Of course, auroras are only one aspect of space weather. They’re like rainbows, because they’re very pretty, and they’re harmless. But space weather can be much more powerful, and can produce much greater effects than mere auroras. That’s why there’s a growing effort to be able to predict space weather by watching the Sun.
A powerful enough solar storm can produce a CME strong enough to damage things like power systems, navigation systems, communications systems, and satellites. The Carrington Event in 1859 was one such event. It produced one of the largest solar storms on record.
That storm occurred on September 1st and 2nd, 1859. It was preceded by an increase in sun spots, and the flare that accompanied the CME was observed by astronomers. The auroras caused by this storm were seen as far south as the Caribbean.
The same storm today, in our modern technological world, would wreak havoc. In 2012, we almost found out exactly how damaging a storm of that magnitude could be. A pair of CMEs as powerful as the Carrington Event came barreling towards Earth, but narrowly missed us.
We’ve learned a lot about the Sun and solar storms since 1859. We now know that the Sun’s activity is cyclical. Every 11 years, the Sun goes through its cycle, from solar maximum to solar minimum. The maximum and minimum correspond to periods of maximum sunspot activity and minimum sunspot activity. The 11 year cycle goes from minimum to minimum. When the Sun’s activity is at its minimum in the cycle, most CMEs come from coronal holes.
NASA’s Solar Dynamics Observatory (SDO), and the combined ESA/NASA Solar and Heliospheric Observatory (SOHO) are space observatories tasked with studying the Sun. The SDO focuses on the Sun and its magnetic field, and how changes influence life on Earth and our technological systems. SOHO studies the structure and behavior of the solar interior, and also how the solar wind is produced.
Several different websites allow anyone to check in on the behavior of the Sun, and to see what space weather might be coming our way. The NOAA’s Space Weather Prediction Center has an array of data and visualizations to help understand what’s going on with the Sun. Scroll down to the Aurora forecast to watch a visualization of expected auroral activity.
NASA’s Space Weather site contains all kinds of news about NASA missions and discoveries around space weather. SpaceWeatherLive.com is a volunteer run site that provides real-time info on space weather. You can even sign up to receive alerts for upcoming auroras and other solar activity.
The Northern Lights have fascinated human beings for millennia. In fact, their existence has informed the mythology of many cultures, including the Inuit, Northern Cree, and ancient Norse. They were also a source of intense fascination for the ancient Greeks and Romans, and were seen as a sign from God by medieval Europeans.
Thanks to the birth of modern astronomy, we now know what causes both the Aurora Borealis and its southern sibling – Aurora Australis. Nevertheless, they remain the subject of intense fascination, scientific research, and are a major tourist draw. For those who live north of 60° latitude, this fantastic light show is also a regular occurrence.
Aurora Borealis (and Australis) is caused by interactions between energetic particles from the Sun and the Earth’s magnetic field. The invisible field lines of Earth’s magnetoshere travel from the Earth’s northern magnetic pole to its southern magnetic pole. When charged particles reach the magnetic field, they are deflected, creating a “bow shock” (so-named because of its apparent shape) around Earth.
However, Earth’s magnetic field is weaker at the poles, and some particles are therefore able to enter the Earth’s atmosphere and collide with gas particles in these regions. These collisions emit light that we perceive as wavy and dancing, and are generally a pale, yellowish-green in color.
The variations in color are due to the type of gas particles that are colliding. The common yellowish-green is produced by oxygen molecules located about 100 km (60 miles) above the Earth, whereas high-altitude oxygen – at heights of up to 320 km (200 miles) – produce all-red auroras. Meanwhile, interactions between charged particles and nitrogen will produces blue or purplish-red auroras.
The visibility of the northern (and southern) lights depends on a lot of factors, much like any other type of meteorological activity. Though they are generally visible in the far northern and southern regions of the globe, there have been instances in the past where the lights were visible as close to the equator as Mexico.
In places like Alaska, Norther Canada, Norway and Siberia, the northern lights are often seen every night of the week in the winter. Though they occur year-round, they are only visible when it is rather dark out. Hence why they are more discernible during the months where the nights are longer.
Because they depend on the solar wind, auroras are more plentiful during peak periods of activity in the Solar Cycle. This cycle takes places every 11 years, and is marked by the increase and decrease of sunspots on the sun’s surface. The greatest number of sunspots in any given solar cycle is designated as a “Solar Maximum“, whereas the lowest number is a “Solar Minimum.”
A Solar Maximum also accords with bright regions appearing in the Sun’s corona, which are rooted in the lower sunspots. Scientists track these active regions since they are often the origin of eruptions on the Sun, such as solar flares or coronal mass ejections.
The most recent solar minimum occurred in 2008. As of January 2010, the Sun’s surface began to increase in activity, which began with the release of a lower-intensity M-class flare. The Sun continued to get more active, culminating in a Solar Maximum by the summer of 2013.
Locations for Viewing:
The ideal places to view the Northern Lights are naturally located in geographical regions north of 60° latitude. These include northern Canada, Greenland, Iceland, Scandinavia, Alaska, and Northern Russia. Many organizations maintain websites dedicated to tracking optimal viewing conditions.
For instance, the Geophysical Institute of the University of Alaska Fairbanks maintains the Aurora Forecast. This site is regularly updated to let residents know when auroral activity is high, and how far south it will extend. Typically, residents who live in central or northern Alaska (from Fairbanks to Barrow) have a better chance than those living in the south (Anchorage to Juneau).
In Northern Canada, auroras are often spotted from the Yukon, the Northwest Territories, Nunavut, and Northern Quebec. However, they are sometimes seen from locations like Dawson Creek, BC; Fort McMurry, Alberta; northern Saskatchewan and the town of Moose Factory by James Bay, Ontario. For information, check out Canadian Geographic Magazine’s “Northern Lights Across Canada“.
The National Oceanic and Atmospheric Agency also provides 30 minute forecasts on auroras through their Space Weather Prediction Center. And then there’s Aurora Alert, an Android App that allows you to get regular updates on when and where an aurora will be visible in your region.
Understanding the scientific cause of auroras has not made them any less awe-inspiring or wondrous. Every year, countless people venture to locations where they can be seen. And for those serving aboard the ISS, they got the best seat in the house!
Speaking of which, be sure to check out this stunning NASA video which shows the Northern Lights being viewed from the ISS:
For more information, visit the THEMIS website – a NASA mission that is currently studying space weather in great detail. The Space Weather Center has information on the solar wind and how it causes aurorae.
Special Guest: Howard Trottier, a physics professor at Simon Fraser University (SFU) in British Columbia, Canada. Dr. Trottier has recently devoted his time to the development of SFU’s unique Astronomy public outreach program. In the heart of SFU’s main campus is a “”Science Courtyard,”” a high-profile public space devoted to astronomy and anchored by a state-of-the art outreach and teaching observatory. You can learn more about this amazing program here.
We’ve had an abundance of news stories for the past few months, and not enough time to get to them all. So we’ve started a new system. Instead of adding all of the stories to the spreadsheet each week, we are now using a tool called Trello to submit and vote on stories we would like to see covered each week, and then Fraser will be selecting the stories from there. Here is the link to the Trello WSH page (http://bit.ly/WSHVote), which you can see without logging in. If you’d like to vote, just create a login and help us decide what to cover!
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