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Our sun is a weirdly 'quiet' star — and that's lucky for all of us

Dark sunspots increase when the sun is more active.
Dark sunspots increase when the sun is more active.
(Image: © NASA/SDO/AIA/HMI/Goddard Space Flight Center)

Thank your lucky stars that the sun is pretty weird, as scientists have learned by comparing its activity with that of similar stars.

In new research, astronomers compared the brightness of our sun over time with data gathered on other stars by NASA's Kepler Space Telescope and by the European Space Agency's Gaia star-mapping mission. The result is a census of stars about the same size of our sun. But compared to these stars, our sun's brightness varies significantly less, suggesting that it is calmer than other stars of about the same size.

"We were very surprised that most of the sun-like stars are so much more active than the sun," Alexander Shapiro, a physicist at the Max Planck Institute for Solar System Research in Germany and a co-author on the new research, said in a statement.

Related: World's largest solar telescope produces never-before-seen images

Scientists are well acquainted with the sun's current behavior, of course, and have astronomical observations of dark spots on its surface going back about 400 years. Those sunspots are crucial information about the activity of the sun: They are driven by the sun's magnetic field and massive outbursts of radiation and matter stem from them.

To understand what the sun was doing before those records begin, scientists can interpret a host of data types, like levels of specific elements in tree rings and ancient ice. With those aids, researchers have constructed estimates of the sun's activity going back about 9,000 years. The modern sun matches that record pretty well, the researchers said — but that doesn't mean those 9,000 years are representative of the sun's 4.6 billion years of existence.

"Compared to the entire lifespan of the sun, 9,000 years is like the blink of an eye," Timo Reinhold, lead author of the new study and an astrophysicist at the Max Planck Institute for Solar System Research, said in the same statement. "It is conceivable that the sun has been going through a quiet phase for thousands of years and that we therefore have a distorted picture of our star."

Reinhold and his colleagues wanted to compare the sun's known activity with what other similar stars are doing. Scientists can't track sunspots on distant stars directly, but these dark patches on a blazing ball of plasma do affect the brightness of the star. Because all stars rotate, sunspots are carried around the star, causing its brightness to fluctuate — and scientists know very well how to track variations in brightness of a star over time. 

The brightness variability of our sun compared with that of KIC 7849521, a sun-like star.  (Image credit: MPS/hormesdesign.de)

That type of data forms the backbone of one of astronomers' main techniques for discovering exoplanets, and NASA's Kepler Space Telescope was tailored to measure tiny changes in the brightness of an individual star over time. So the researchers behind the new study went digging in that data.

The astronomers narrowed down a collection of tens of thousands of stars by focusing on those with about the same surface temperature, surface gravity, age and metallicity as our sun. Then, they split these stars into two batches: one containing 369 stars that rotate every 20 to 30 days and one with 2,529 stars that scientists haven't been able to calculate a rotation period for. (The sun rotates every 24.5 days, but that spin likely wouldn't be detectable to alien astrophysicists using the same techniques humans have, so both of these groups of stars are important.)

The researchers then analyzed both these groups of stars to understand their activity levels and how they compare with the sun. Stars with known rotation rates were on average much more active than our sun has been over the past 9,000 years — about five times more active. The stars without tracked rotations were less active, much more in line with the sun.

That split poses a puzzle for scientists: Either there's something fundamentally different between clockable stars and unclockable ones, or something has been making the sun much quieter than stars like it for at least the past 9,000 years.

Right now, there's no way to tell which is correct. But it's definitely not a bad thing that our sun is relatively calm: Its outbursts can endanger our technology in orbit and on Earth's surface, and if it were very, very active, the sun's temper could threaten life itself. Fortunately, there's no sign the sun will get rowdy soon, and scientists have predicted that the upcoming 11-year solar cycle should be reasonably tame.

The research is described in a paper published May 1 in the journal Science.

Email Meghan Bartels at mbartels@space.com or follow her @meghanbartels. Follow us on Twitter @Spacedotcom and on Facebook.

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  • rod
    Very interesting report. Here is another link on the subject, The Sun is less active than other solar-like stars

    "Activity levels of Sun-like stars Magnetic activity on the Sun leads to solar flares, coronal mass ejections, and other space weather that affects Earth. Similar activity on other stars may determine the habitability of any orbiting exoplanets. Reinhold et al. analyzed brightness variations of stars observed with the Kepler and Gaia space telescopes to infer their activity levels (see the Perspective by Santos and Mathur). They found that the Sun was less active than most of the 369 solar-type stars in their sample (those with the most similar physical properties). It remains unclear whether the Sun is permanently less active than other stars of its type or if its activity levels vary over many thousands or millions of years. Abstract The magnetic activity of the Sun and other stars causes their brightness to vary. We investigated how typical the Sun’s variability is compared with other solar-like stars, i.e., those with near-solar effective temperatures and rotation periods. By combining 4 years of photometric observations from the Kepler space telescope with astrometric data from the Gaia spacecraft, we were able to measure photometric variabilities of 369 solar-like stars. Most of those with well-determined rotation periods showed higher variability than the Sun and are therefore considerably more active. These stars appear nearly identical to the Sun except for their higher variability. Therefore, we speculate that the Sun could potentially also go through epochs of such high variability."

    The Sun spins about 2 km/s at its equator, some stars in this study spin near 3 km/s. Another report shows the Sun is a very round object, Sun's Almost Perfectly Round Shape Baffles Scientists Folks can compare our Sun to other stars reported where the exoplanets are located, http://exoplanet.eu/ Looks like our Sun is very good for life here on Earth.
    Reply
  • Abdelazziz
    Interesting, but the chart shown includes less than 5 years of Solar Activity changes, the fact that the KIC 7849521 star has a much larger variability will not affect forecasts about Global Warming, as it could be averages, mean, Area Under Curve what matters, a not so minutely precise measurement, but giving a more practical information.
    A fact is that usualy, solar cycle has a maximum each 11 years, but the nearest maximum arrived with years of delay, and when Sunspots came back, this was along with extreme weather, as Kathrina (and her waves).
    If tree rings, isotopes in permanent ice allow having an image of solar activity, not in years, but millennia, this would be the data useful to be shown in charts.
    A doubt, not long ago, comets were seen hitting the solar surface: are there any materials that, incorporated to solar surface, even in minute amounts, could change the light and other radiation arriving to us? Star Wars?
    Reply
  • rod
    Observations over 12 years show the Sun is a very stable star for life on Earth, “An instrument on the European/NASA SOHO solar observatory has imaged the Sun some 500,000 times in the past 12 years. This consistent, easily compared series of images shows that the Sun’s size has been rock-steady since 1998 to about 1 part in 50,000. This despite the fact that the Sun’s brightness varies by about 1 part in 1,000 during the 11-year sunspot cycle, due to the waxing and waning of surface activity.”, ref - The Rock-Steady Size of the Sun, News Notes, Sky & Telescope 120(3):16-18, 2010. As the space.com report title says *...and that's lucky for all of us*. Luck as a cause and effect mechanism is basically an appeal to *stuff happens* :)
    Reply
  • Wolfshadw
    Given that our star is in a relatively quiet part of the galaxy neighborhood, one wonders where in the galaxy are these other stars that are being observed. Are they in more dense clusters of stars in a spiral arm of the galaxy?

    -Wolf sends
    Reply
  • matthewota
    Of course our Sun is well behaved. Otherwise, we would not be around to contemplate it.
    Reply
  • foxpup
    We may have one more term to add to the Drake Equation here. Actually this is the kind of thing that makes me seriously doubt the usefulness/truthfulness of the Drake Equation. You never really know how many terms you actually need when you have a sample of one. Consequently I don't lose any sleep being bothered by the Fermi Paradox either since that's just as questionable of a concept and for the same reason.
    Reply
  • matthewota
    foxpup said:
    We may have one more term to add to the Drake Equation here. Actually this is the kind of thing that makes me seriously doubt the usefulness/truthfulness of the Drake Equation. You never really know how many terms you actually need when you have a sample of one. Consequently(,) I don't lose any sleep being bothered by the Fermi Paradox either since that's just as questionable of a concept and for the same reason.
    What does this have to do with the topic? We are discussing
    "Our sun is a weirdly 'quiet' star — and that's lucky for all of us".
    Reply
  • foxpup
    matthewota said:
    What does this have to do with the topic? We are discussing
    "Our sun is a weirdly 'quiet' star — and that's lucky for all of us".
    It's because this discovery about the Sun could cause those who think about the Drake equation to change the number of terms. If we have a wierd (rare) sun that needs to be taken into account. Unexpected needs to change the Drake equation erodes at its credibility which also erodes at the significance of the Fermi Paradox since it stands otop the Drake equation.
    Reply
  • rod
    foxpup said:
    It's because this discovery about the Sun could cause those who think about the Drake equation to change the number of terms. If we have a wierd (rare) sun that needs to be taken into account. Unexpected needs to change the Drake equation erodes at its credibility which also erodes at the significance of the Fermi Paradox since it stands atop the Drake equation.

    Good observation. The recent report on Proxima Centauri b exoplanet shows similar problems for red dwarf star hosts. This red dwarf has some 400x more flares in X-rays than our quiet Sun, https://forums.space.com/threads/proxima-b-the-closest-alien-planet-we-know-may-be-even-more-earth-like-than-we-thought.31442/
    Reply
  • foxpup
    rod said:
    Good observation. The recent report on Proxima Centauri b exoplanet shows similar problems for red dwarf star hosts. This red dwarf has some 400x more flares in X-rays than our quiet Sun, https://forums.space.com/threads/proxima-b-the-closest-alien-planet-we-know-may-be-even-more-earth-like-than-we-thought.31442/
    Although the extra 400x flares and the X-rays would be a threat to life as we know it, it sure would be fantastic to look at. Our ordinary boring sun is my favorite star in the sky and I often do the forbidden and use my red Edmond Scientific bong-shaped astroscan 4" telescope as a projector to project 2 foot size images of the sun on handy surfaces to look at whatever solar features are visible. More sunspots, flares, and prominences would be amazing to see. Still, its better the way it is. :-)
    Reply