17th Century Solar Oddity Believed Linked To Global Cooling Is Rare Among Nearby Stars

Science Daily ^ | 6-3-2004 | UC Berkeley

[blam]

Source: University Of California - Berkeley

Date: 2004-06-03

17th Century Solar Oddity Believed Linked To Global Cooling Is Rare Among Nearby Stars

Berkeley - A mysterious 17th century solar funk that some have linked to Europe's Little Ice Age and to global climate change, becomes even more of an enigma as a result of new observations by University of California, Berkeley, astronomers.

For 70 years, from 1645 until 1714, early astronomers reported almost no sunspot activity. The number of sunspots - cooler areas on the sun that appear dark against the brighter surroundings - dropped a thousandfold, according to some estimates. Though activity on the sun ebbs and flows today in an 11-year cycle, it has not been that quiet since.

Since 1976, when it was pointed out that this lengthy period of low sunspot activity, the so-called Maunder minimum, coincided with the coldest part of the Little Ice Age in Europe and North America, astronomers have been searching nearby sun-like stars for examples of stellar minima. They have hoped to determine how common such minima are and to predict the next solar minimum - and perhaps the next period of global cooling.

Now, data from a group of UC Berkeley astronomers cast doubt on the hundreds of stars thought to be examples of stellar minima analogous to the quiet period the sun experienced 300 years ago.

In a poster to be presented Monday, May 31, at the Denver meeting of the American Astronomical Society, UC Berkeley graduate student Jason Wright shows that nearly all the supposedly sun-like stars displaying minimal activity are, in fact, much brighter than and significantly different from the sun and therefore not examples of Maunder minima. The findings throw into question all studies using these stars to make inferences about the sun's own activity and future minima, Wright said.

"Star surveys typically find that 10 to 15 percent of all sun-like stars are in an inactive state like the Maunder minimum, which would indicate that the sun spends about 10 percent of its time in this state," Wright said. "But our study shows that the vast majority of stars identified as Maunder minimum stars are well above the main sequence, which means they're not sun-like at all, but are either evolved stars or stars rich in metals like iron and nickel. To date, we've found no star that is unambiguously a Maunder minimum star."

"We thought we knew how to detect Maunder minimum stars, but we don't," he said.

The main sequence is a region where normal, steady-burning stars cluster when plotted on a chart of color versus brightness. As stars age, however, they get redder and brighter - becoming what are called subgiant stars - and move upward off the main sequence. The sun has been on the main sequence for about 5 billion years, ever since it settled down after igniting hydrogen fusion in its core, and will remain there for another 5 billion years until it starts to swell and become a subgiant.

"The fact is, we still don't understand what's going on in our sun, how magnetic fields generate the 11-year solar cycle, or what caused the magnetic Maunder minimum," said Wright's advisor, Geoffrey Marcy, professor of astronomy at UC Berkeley. "In particular, we don't know how often a sun-like star falls into a Maunder minimum, or when the next minimum will occur. It could be tomorrow."

The drop in solar activity in the late 17th and early 18th centuries was drawn to the world's attention in 1893 by English astronomer Edward Walter Maunder, who also noted a dip during the same period in the intensity and frequency of the northern lights, which are caused by storms on the sun. Again, in 1976, astronomer John Eddy reviewed various pieces of evidence for the Maunder minimum and concluded not only that it was real, but cited a 1961 paper linking the minimum with a contemporaneous period of cooling throughout Europe, perhaps due to decreased energy output from the sun. The sun, and stars like the sun, are dimmer when inactive.

The idea of a Maunder minimum is controversial, however, because no one really knows how closely people were observing the sun in the mid-1600s, a mere 40 years after the invention of the telescope. No record of solar activity exists before the Maunder minimum, though a surge in activity signaled its end in 1714.

Uncertainty also surrounds the cause of the Little Ice Age, which began around 1300 A.D. and lasted for several hundred years. Characterized by colder than normal winters and cool summers throughout the Northern Hemisphere, it may have been caused by greenhouse gases and particulates spewed into the atmosphere by volcanoes, or by fluctuations in the sun's output.

Many climate experts take the Maunder minimum seriously, however, and astronomers have put together a long list of stars supposedly exhibiting the same dip in activity, as evidenced by decreased emission from the element calcium in the star's atmosphere. Solar activity is characterized by strong magnetic fields that heat the sun's upper atmosphere, or chromosphere, to some 8,000 to 10,000 degrees Kelvin, exciting calcium to emit blue light.

The question, Wright said, is whether the cause of decreased calcium emission is a stellar Maunder minimum or something else, like age - stars spin more slowly as they age, lose their magnetic dynamo and no longer produce magnetic fields or spots - or high metal content. "We've now found that it's not from Maunder minima," he said.

"What astronomers have assumed is that sun-like stars going through a stellar funk are actually very, very old stars whose magnetic fields have turned off forever. They are not in a temporary Maunder minimum, but a permanent one. They're dead," Marcy said. "The sun will be in that state in 4 billion years or so."

"This implies that if other stars do undergo Maunder minima of their own, then it is either a rare occurrence nearly undetected in activity surveys or it is not necessarily indicated by low calcium ... emission levels," Wright wrote. Therefore, he added, some other criterion is needed to discern those stars in a stellar downturn.

The problem with stars thought to be in a Maunder minimum went unnoticed because it wasn't until 1998 that the Hipparcos satellite was launched and began determining the precise distances to many nearby stars. It then became possible to calculate the absolute brightness of these stars, and to place them precisely on a color-brightness plot, known as a Hertzsprung-Russell diagram.

Wright decided to look systematically at Maunder minimum stars after he and Marcy noticed that many seemingly inactive nearby stars were actually brighter than main sequence stars. They have collected spectra of more than 1,000 nearby stars to look for evidence of planets.

In his analysis, Wright used Hipparcos data on distance to determine the absolute brightness of several thousand nearby stars surveyed not only by Marcy's California and Carnegie Planet Search Program but also by other projects, such as the Mount Wilson H-K Project and Project Phoenix. He noted that some of the stars previously identified as Maunder minimum stars may be metal-rich stars, which also burn brighter than our sun and show less activity. Further analysis of nearby stars is needed to characterize these quiet stars.

The findings, which have been submitted to Astrophysical Journal, resulted from work supported by Sun Microsystems, the National Aeronautics and Space Administration, and the National Science Foundation.

[Marine_Uncle]

Thanks Ernest.

[Ernest_at_the_Beach]

Doing a search on Mauder Minima stars...turning up a few thinks:

Lets start with this: H-K Project
Extra-cyclic activity

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When examining the long-term direct record of sunspot observations, it is immediately apparent that the length and amplitude of the 11-year sunspot cycle is not constant. The figure at right shows the yearly sunspot number over the past 380 years. At the beginning of this record, it appears that the sunspot cycle apparently ceased for almost 70 years. One simple explanation would be that there simply were no observations during that time. Another would be that astronomers of that time period were simply not very good at observing, or did not make accurate records of the sunspot number.

However, neither of these explanations are true. First of all, some of the astronomers of that time period were Galileo, Scheiner, Hevelius, Halley, and Herschel. Their observations of other celestial bodies show their prowess; incompetence simply was not the issue. There is no reason to believe that they ignored the Sun. Several reports of sunspots during this time period actually made note of the fact that their seeing a sunspot was considered out of the ordinary for that time period.

Therefore, we are forced to conclude that the Sun does experience occasional lulls in its activity. Using other proxies of long-term activity, such as the ¹⁴C abundance, we can see that the Sun goes into these quiescent periods every few centuries. At present we seem to be experiencing the opposite phenomenon; the most recent four cycles are among the most active ever recorded.

Understanding what causes the 11-year sunspot cycle has eluded scientists for centuries, so it goes without saying that we don't understand why it should vary as much as it does, let alone almost vanish completely from time to time. The 30-year record of activity for sun-like stars compiled by the HK Project is just beginning to investigate this phenomenon.

Extra-Cyclic Activity in Solar-like stars

A survey of stars close to the Sun in mass and activity shows the distribution at left. The arrows above the distribution show the range of activity seen by the Sun from the expected activity level in the Maunder Minimum to sunspot maximum, with the line left of center indicating the activity at sunspot minimum. From this, it appears that as many as 25% of the stars surveyed could be in a Maunder Minimum-like state. Therefore, the Sun might spend up to 25% of its time at present under similar conditions.

This figure on the right, shows a similar distribution of activity for two open clusters, Messier 67, which is nearly the same age as the Sun, and NGC 752 which is about 2 billion years younger than the Sun. The arrow above the M67 histogram has the same meaning as in the previous plot. Using open clusters to test the frequency of Maunder minima is preferred because it can be assumed that the age of all the stars in the cluster is nearly equal. Therefore, the distribution observed is more likely to be accurate than using field stars whose ages are not well-known. The distribution for M67 is similar to the field star distribution, and about 1/4 of the stars have low activity similar to the Maunder Minimum. In comparison, the younger open cluster of NGC 752 have very few inactive stars, but the fact that there is a few suggests that Maunder minimum episodes could occur, but a lower frequency than that of stars closer in age to the Sun.

Monitoring Extra-Cyclic Activity

Unfortunately, the Maunder Minimum occurred just after the invention of the telescope. Therefore there are few records immediately preceeding it to see how the Sun behaved as it was beginning. There are records at the end of the Maunder Minimum, and one feature appears to be that the length of sunspot cycle varied more than it does at the present, from 8 to 13 years. In the hopes that we can learn more about extra-cyclic activity, the HK Project has begun observing several inactive stars. Some of these stars may be in Maunder Minimum states, and therefore, long-term monitoring may show changes in their behavior as they come out of this inactive phase.

At the same time, a few of the stars which have been observed since 1966 are beginning to show long-term behavior. In the left panel of the above figure, two stars with similar mass and rotation period are shown. Because their mass and rotation are similar, they should have nearly the same level of activity. However, the activity of 54 Piscium (HD 3651) has been decreasing steadily since before 1966. The most recent activity maximum is as low as the activity minimum seen in the early 1970's. This star could be entering a Maunder minimum. On the right is HD 9562, a star close to the Sun in mass. It's activity has only a very small increasing trend over 30 years. From its spectrum, the rotation period must be less than 25 days (i.e., close to the Sun's) but its activity it much lower than the Sun's. Therefore, it is very likely that this star is currently in a Maunder Minimum.

Continued observations of all of these stars will hopefully provide clues as to what the Sun's behavior will be over the coming centuries. An important effect of this research is the investigation of how long-term variations of solar activity like the Maunder Minimum affect the Earth. The time period of the Maunder Minimum also corresponds to a period called the ``Little Ice Age'', when summers in Europe were short and winters were severe. Therefore, further analysis of extra-cyclic stellar activity could provide important clues to a better understanding of changes in the Sun and their impact on the Earth's climate.

[Ernest_at_the_Beach]

From WUWT?:

The Day The Earth Cooled

************************************EXCERPT*********************************

Posted on September 26, 2008 by Anthony Watts

This is a familar set of issues in one article. – Anthony

---

By INVESTOR’S BUSINESS DAILY | Posted Thursday, September 25, 2008 4:20 PM PT

Environment: The solar wind is slowing, but Al Gore is still spewing hot air. The Oscar winner is promoting civil disobedience to stop energy and economic growth as the first U.S. emissions cap-and-trade program begins.

Speaking before Bill Clinton’s Global Initiative, junk science advocate Gore called on young people to take the law into their own hands because the climate, he claims, is a-changin’. He told the gathering in New York City that “the world has lost ground to the climate crisis” and the time for action is now.

“If you’re a young person looking at the future of this planet and looking at what is being done right now, and not done, I believe we have reached the stage where it is time for civil disobedience to prevent the construction of new coal plants that do not have carbon capture and sequestration,” Gore said to loud applause.

His comments come two weeks after a British jury acquitted six Greenpeace activists accused of causing property damage at a power plant. The jury felt the “protest” was acceptable because the “protesters” feared the plant would contribute to global warming.

Luddites of the world, unite!

On the same day Gore spoke, scientists involved in NASA’s Ulysses project reported that the intensity of the sun’s solar wind was at its lowest point since the beginning of the space age – one more indication that the sun, the biggest source of energy affecting the Earth, is getting quiet.

The weaker solar wind appears to be due to changes in the sun’s magnetic field, but the cause is unknown. Sunspots, which normally fluctuate in 11-year cycles, are at a virtual standstill. In August, the sun created no visible spots. The last time that happened: June 1913.

The results of the Ulysses spacecraft’s mission, according to Jet Propulsion Laboratory project scientist Ed Smith, show that “we are in a period of minimal activity that has stretched on longer than anyone anticipated.”

The consequences for Earth are enormous. The lack of increased activity could signal the start of what is known as a Maunder Minimum, an event that occurs every couple of centuries and can last as long as a century. It leads to extended periods of severe cooling such as what happened during the Little Ice Age.

It may already be happening. The four major agencies tracking Earth’s temperature, including NASA’s Goddard Institute, report that the Earth cooled 0.7 degree Celsius in 2007, the fastest decline in the age of instrumentation, putting us back to where the Earth was in 1930.

The climate is changing, but not in the direction Al Gore thinks. As the Earth demonstrably cools under a weakening sun, a 10-state coalition on Thursday held the nation’s first carbon allowance auction to deal with a warming trend that may have ended a decade ago.

They will impose a minor league version of the Lieberman-Warner economy-killing cap-and-trade rationing system in which emissions are limited by a progressively lowered cap. Emission permits are auctioned off by government, making it a cap-and-tax system. Permits can be traded or sold between companies like baseball cards.

The Lieberman-Warner bill would mandate emission cuts of 44% below 2007 levels. The Environmental Protection Agency estimates that it would cost as much as $3 trillion a year in lost GDP in an economy of roughly $14 trillion. It dwarfs the current financial crisis. But then, it’s for a good cause – right, Al?

The New York-based Regional Greenhouse Gas Initiative, launched Thursday, strives to freeze CO2 emissions through 2014 and then gradually reduce them to 10% below current levels by 2018. The states participating are Connecticut, Delaware, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Rhode Island and Vermont.

Like its bigger cousin, it’s a job- and growth-killing plan in a time of economic crisis. As the sun slows and the Earth cools, it’ll mean higher energy prices during colder and snowier winters.

Al Gore’s hippie legions may have to wear their winter coats.

[Marine_Uncle]

Their explanations seem reasonable. Of course Of course it would be nice to have a time machine loaded with various type spectrometers and some good scientist and techs on board. :)