The Sun kick starts its cycle once again

By Phil Plait | January 14, 2008 11:38 am

The Sun is a variable star. Sunspots — dark regions on the surface of the Sun — increase in number over the years, peak, and then slowly decline once again. The pattern repeats every 11 years. Sunspots are regions of magnetic activity, and that is what fuels the massive eruptions of solar flares and coronal mass ejections (CMEs) off the Sun. These can play havoc with all sorts of human activities: radio communications, GPS satellites, and even lay waste to our power grid (Quebec had a massive blackout in 1989 due to solar activity).

Obviously, astronomers pay close attention to the Sun.

The last cycle waned a few years back, and our nearest star has been pretty quiet. The predictions were that the new cycle would start up soon… and it looks like it’s poking its head through the door.

This image (from SOHO) shows the newest spot to blemish the Sun. We can tell it’s part of the new cycle because of the Sun’s magnetic field: sunspots reverse their (magnetic north and south) polarity every cycle, and this spot shows that reversal. So welcome the first spot for Cycle 24!

The spot looks dinky, but don’t be fooled. First of all, it’s several thousand kilometers across — the Sun is big big big. Second, we’ve already seen some activity from it; two blasts of energy have emanated from it since it was spotted a week ago. Magnetic field lines get tangled up, and can suddenly reconnect, making huge explosions on the surface (which can trigger solar flares and CMEs). There is a cool movie of this available, too.

I didn’t know very much about the details of the Sun’s magnetic field and cycles until recently, which is when I started researching them for my chapter on solar flares for my upcoming book Death from the Skies! … and then I learned a lot. This is a fascinating topic, and astronomers discover more about the Sun literally every day. I’ll be very excited to keep track of Cycle 24, at the very least so I can figure out how to milk it for book publicity.

Comments (30)

  1. Stephen

    I’ll be very excited to keep track of Cycle 24, at the very least so I can figure out how to milk it for book publicity.
    At least you’re honest.

  2. I’ll be very excited to keep track of Cycle 24, at the very least so I can figure out how to milk it for book publicity.

    Colbert not biting? Oh dear.

  3. zeb

    From my very crude image analysis, the spot is around 16,000 km across, or about 25% bigger than Earth.

  4. gopher65

    BA says:
    “The Sun is a variable star.”

    Errr… is Sol really a variable star, or were you using that in the colloquial sense of the word? I thought our sun was a relatively stable star?

  5. seb

    “The Sun is a variable star” – wrong.

  6. Fred S

    Hey, think about it, everybody–this only happens once every 11 years. It’s way bigger than New Years Day–why don’t astronomers have a party for this? 2nd Q: Whose house/observatory and who’s bringing the champagne?

  7. Melusine

    The Sun is a variable star, so they say:

    TheSolar Maximum Mission(SMM)

    in the 1980′s established that the Sun was a variable star whose total luminosity changed in phase with the solar magnetic cycle.

    http://umbra.nascom.nasa.gov/soho/ssmp/SOHO_max_prop_03.html

  8. Fred S

    3rd Q: Who’s bringing the H alpha filter?

  9. Well, it’s not a variable star in the sense that Mira or Algol are variable stars. It’s just not strictly fixed in its luminous output. But as far as I know, total solar irradiance at Earth’s orbit has stayed between 1363 and 1367 W m^-2 for the past 400 years or so, including the Maunder Minimum.

  10. Murff

    Cycle 24…can I assume this is the 24th cycle since we discovered it the sun has cycles?

    ** I’ve never really been that interested in the Sun :( **

  11. The Lord has given me a sign! I have been reading Ray Comfort’s book, God Doesn’t Believe in Atheists, over the past few days. On page 120, in the chapter listing “prophetic facts,” Ray tells of a possible prophecy related to sun spots! I just read that, and now I am seeing this post about them too! God is reaching out to me!

    Excerpt from page 120:
    “There will be ‘signs in the sun’ (Luke 21:25). This is possibly a reference to sun spots which, according to the dictionary, are ‘dark, irregular spots appearing periodically on the sun’s surface.’”

    Seriously though, this is one of the funniest books I have ever read.

  12. My previous post was flagged as SPAM. :(

  13. DrFlimmer

    The best part of this new cycle is: We have two very different predictions.
    There are some guys claiming the cycle will be rather quiet and harmless. But there are some other guys saying that the cycle will be extremly heavy and maybe dangerous for our satalites out there!
    We will see what will happen and then we may be able to determine which theory is true…. or maybe both are wrong. Nevertheless, we are facing 11 interesting years!

  14. As a ham radio operator, I was very happy when I heard about the start of cycle 24 last week, as it means that long distance HF communications will improve over the next few years.

    It’s been pretty bad these last 18 months or so with many months of NO sunspots and very poor long distance radio propagation.

  15. While sunspots on their own darken the Sun by a fraction of a percent, they are surrounded by regions called faculae which actually brighten the Sun overall. So, ironically, when the sunspots are at their peak, the Sun is actually brighter by about 0.1%.

    The stuff you learn while writing a book…

  16. Crux Australis

    Faculae…I can see my class full of 16-year-olds having a ton of fun with that word. Faculae, faculae, FAC-ulae!

  17. chris H

    hey doc bad astro, isnt the solor maximum in 2012? hmmm, coinencidence? i’ll let you decide

  18. Michael Lonergan

    Just curious as to why this is called “Cycle 24?”

  19. gopher65

    Melusineon says:

    in the 1980’s established that the Sun was a variable star whose total luminosity changed in phase with the solar magnetic cycle.

    I really hope they aren’t going with that definition of “variable star”. If they are, then every star in the entire universe would be classified as a variable!

  20. Melusine

    gopher65:

    I really hope they aren’t going with that definition of “variable star”. If they are, then every star in the entire universe would be classified as a variable!

    Dr. Sten Odenwald appears to say just that here:
    http://www.astronomycafe.net/qadir/q217.html

  21. chris H, nice try, but bzzzzt. The sunspot maximum will be on or about 2012, but the maximum activity on the Sun (strongest flares and CMEs) peaks a year or two after the sunspot number peaks.

  22. Fergus Gallagher

    Just to be a pedant, the solar cycle is actually 22-years. It looks like 11 because we don’t distinguish between the northern and southern magnetic polarities.

    As an aside, who realises that the Earth’s North Pole is actually a magnetic south pole. Think about it. How else would compasses work?

  23. csrster

    The Sun is most definitely considered a variable star, at least by people who actually work in the field. It’s total luminosity varies over an 11 year cycle but it also shows other forms of variation – e.g. five minute and three minute oscillations at optical and UV wavelengths as well as irregular variations in UV and X-Ray.

    Phil is right about the rather weird effect that the Sun is brighter (as seen from the Earth) at solar maximum, even though a large sunspot group will actually cause a short-period dip in the solar brightness. A more subtle question is how the total luminosity of the Sun varies over the solar cycle. Measurements made at the Earth only show how much radiation the Sun is emitting along, roughly speaking, its equator. But is there an increase in luminosity at all latitudes or are we just seeing a redistribution of the radiation so that the Sun’s emission becomes temporarily less isotropic.? The last I checked, that was actually an open question.

  24. JackC

    For those asking why this is “Cycle 24: http://en.wikipedia.org/wiki/Solar_cycle

    Basically, the early/mid 1800s found Schwabe “discovering” the cycle, and tracking it back in time. It became convention to number the cycle starting in 1755 as “1″

    JC

  25. Justin

    “As an aside, who realises that the Earth’s North Pole is actually a magnetic south pole. Think about it. How else would compasses work?”

    Interesting…please explain?

  26. We are all excited here at the High Altitude Observatory in Boulder (Phil, wanna tour?) about the new solar cycle. A model developed by our scientists (M. Dikpati et al) has predicted that this cycle should be the strongest in over 60 years. Cross your fingers!

    We take solar observations in H-alpha and He-I every three minutes from our observatory in Hawaii.

    You can check out the latest images at the MLSO homepage. Click on “Data and movies” in the banner to get daily movies.

  27. I haven’t observed the sun with my PST since the new cycle started due to lousy weather, but I have one question. How do scientists determine the polarity of an active region or sunspot? It would be difficult to hold a compass up to it to check. Is there some difference that can be detected through a telescope in white or h-a light?

  28. csrster

    Wayne – that’s a damn good question. The polarity of sunspots was first measured by none other than George Ellery Hale whose name most people associate with night-time astronomy (and not only because his name is attached to the big telescope at Palomar). But Hale was also one of the great pioneers of solar astronomy. He is credited as co-inventor of the spectroheliograph, which allows one to make monochromatic images of the Sun.

    Magnetic fields can be measured as a result of the Zeeman effect which causes certain spectral lines to be split in a pattern from which the strength and polarity of the magnetic field can be deduced. Hale and his coworkers were the first to determine how the polarity varies within sunspot groups, between the two solar hemispheres, and with time during the solar cycle.

  29. Wayne Reed

    Thank you csrster for the good description,

    I have seen several reports on this polarity reversal without mention of how it is determined. I was hoping it was something I could confirm with my H-A PST, but I guess it takes more sofisticated techniques than I can muster.

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