APOD: Solar Minimum versus Solar Maximum (2023 Dec 11)

[APOD Robot]

Solar Minimum versus Solar Maximum

Explanation: The surface of our Sun is constantly changing. Some years it is quiet, showing relatively few sunspots and active regions. Other years it is churning, showing many sunspots and throwing frequent Coronal Mass Ejections (CMEs) and flares. Reacting to magnetism, our Sun's surface goes through periods of relative calm, called Solar Minimum and relative unrest, called Solar Maximum, every 11 years. The featured video shows on the left a month in late 2019 when the Sun was near Solar Minimum, while on the right a month in 2014 when near Solar Maximum. The video was taken by NASA's Solar Dynamic Observatory in far ultraviolet light. Our Sun is progressing again toward Solar Maximum in 2025, but displaying even now a surface with a surprisingly high amount of activity.

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[Ann]

The Sun may be undergoing minimums and maximums (which is caused by its magnetism), but it is still darn quiet for a star of its class!

A comparison of the changes in the Sun’s brightness due to sunspots over time (top) to that of a star very much like it (bottom). On average, the Sun changes less than other stars, meaning it’s more quiet magnetically. Credit: MPS / hormesdesign.de

---

Phil Plait of SYFY wrote:

Astronomers have determined that, on average, the Sun is quieter than other stars magnetically, and it's not clear why...

(T)he scientists who did the new research turned to the Kepler observatory, which for three years stared at a single spot in space to look for exoplanets, planets orbiting other stars. It did this by taking frequent brightness measurements of 150,000 stars, looking for dips in brightness when planets passed in front of them, making mini-eclipses. And that means Kepler got a lot of brightness measurements of the stars, which is perfect for this study...

In the end they wound up with long-term Kepler data for 365 solar-type stars. They also had a group of over 3,500 stars that were very much like the Sun but for which no rotation period was known. Then they compared the changes in those stars' brightness with the Sun's.

What they found is surprising: The Sun is much quieter than other stars like it! While the Sun's median brightness variation is 0.07%, the other stars had a median of 0.36%, five times higher! That's even twice as much as the Sun's maximum variation of 0.2%.

Ann

[VictorBorun]

The Sun may be undergoing minimums and maximums (which is caused by its magnetism), but it still darn quiet for a star of its class!

A comparison of the changes in the Sun’s brightness due to sunspots over time (top) to that of a star very much like it (bottom). On average, the Sun changes less than other stars, meaning it’s more quiet magnetically. Credit: MPS / hormesdesign.de

---

Phil Plait of SYFY wrote:

Astronomers have determined that, on average, the Sun is quieter than other stars magnetically, and it's not clear why...

(T)he scientists who did the new research turned to the Kepler observatory, which for three years stared at a single spot in space to look for exoplanets, planets orbiting other stars. It did this by taking frequent brightness measurements of 150,000 stars, looking for dips in brightness when planets passed in front of them, making mini-eclipses. And that means Kepler got a lot of brightness measurements of the stars, which is perfect for this study...

In the end they wound up with long-term Kepler data for 365 solar-type stars. They also had a group of over 3,500 stars that were very much like the Sun but for which no rotation period was known. Then they compared the changes in those stars' brightness with the Sun's.

What they found is surprising: The Sun is much quieter than other stars like it! While the Sun's median brightness variation is 0.07%, the other stars had a median of 0.36%, five times higher! That's even twice as much as the Sun's maximum variation of 0.2%.

Ann

what are the "365 solar-type stars"? Are they of the same mass and age, or do they share Sun's metallicity too?

[Ann]

The Sun may be undergoing minimums and maximums (which is caused by its magnetism), but it still darn quiet for a star of its class!

A comparison of the changes in the Sun’s brightness due to sunspots over time (top) to that of a star very much like it (bottom). On average, the Sun changes less than other stars, meaning it’s more quiet magnetically. Credit: MPS / hormesdesign.de

---

Phil Plait of SYFY wrote:

Astronomers have determined that, on average, the Sun is quieter than other stars magnetically, and it's not clear why...

(T)he scientists who did the new research turned to the Kepler observatory, which for three years stared at a single spot in space to look for exoplanets, planets orbiting other stars. It did this by taking frequent brightness measurements of 150,000 stars, looking for dips in brightness when planets passed in front of them, making mini-eclipses. And that means Kepler got a lot of brightness measurements of the stars, which is perfect for this study...

In the end they wound up with long-term Kepler data for 365 solar-type stars. They also had a group of over 3,500 stars that were very much like the Sun but for which no rotation period was known. Then they compared the changes in those stars' brightness with the Sun's.

What they found is surprising: The Sun is much quieter than other stars like it! While the Sun's median brightness variation is 0.07%, the other stars had a median of 0.36%, five times higher! That's even twice as much as the Sun's maximum variation of 0.2%.

Ann

what are the "365 solar-type stars"? Are they the same mass and age, or do they share Sun's metallicity too?

Out of 150,000 stars, the scientists picked the 365 ones that were the most Sunlike in terms of temperature, metallicity, chemical composition, surface gravity and rotation. These magnetism of these stars was compared with the magnetism of the Sun.

Ann

[VictorBorun]

The Sun may be undergoing minimums and maximums (which is caused by its magnetism), but it still darn quiet for a star of its class!

A comparison of the changes in the Sun’s brightness due to sunspots over time (top) to that of a star very much like it (bottom). On average, the Sun changes less than other stars, meaning it’s more quiet magnetically. Credit: MPS / hormesdesign.de

---

Ann

what are the "365 solar-type stars"? Are they the same mass and age, or do they share Sun's metallicity too?

Out of 150,000 stars, the scientists picked the 365 ones that were the most Sunlike in terms of temperature, metallicity, chemical composition, surface gravity and rotation. These magnetism of these stars was compared with the magnetism of the Sun.

Ann

That's quite alarming! We can be well heading to a more active Sun's age

[MelvzLuster]

Our Sun's age is 4.6 billion years and is predicted to go bigger in the year 3937, so we better prepare now for our future's sake. Correct!

[Bird_Man]

The Sun may be undergoing minimums and maximums (which is caused by its magnetism), but it still darn quiet for a star of its class!

A comparison of the changes in the Sun’s brightness due to sunspots over time (top) to that of a star very much like it (bottom). On average, the Sun changes less than other stars, meaning it’s more quiet magnetically. Credit: MPS / hormesdesign.de

---

Phil Plait of SYFY wrote:

Astronomers have determined that, on average, the Sun is quieter than other stars magnetically, and it's not clear why...

What they found is surprising: The Sun is much quieter than other stars like it! While the Sun's median brightness variation is 0.07%, the other stars had a median of 0.36%, five times higher! That's even twice as much as the Sun's maximum variation of 0.2%.

Ann

What would be the effect to life on Earth if the Sun's activity was more typical? Is this unique quality of the Sun one of the reasons life, as we know it, exists on Earth?

[Chris Peterson]

Our Sun's age is 4.6 billion years and is predicted to go bigger in the year 3937, so we better prepare now for our future's sake. Correct!

Uh... no.

[johnnydeep]

Our Sun's age is 4.6 billion years and is predicted to go bigger in the year 3937, so we better prepare now for our future's sake. Correct!

Uh... no.

Yeah, I did a few searches using "year 3937" and "sun" and came up empty. This sure sounds like some unfounded religious or pseudo-science "prediction", but I'm curious where the OP got it from. "Bigger" could also mean different things: a lot more sunspots, more coronal mass ejections, significantly warmer, or actually larger in diameter. But changes in any of those over the next 1900 years, outside of the normal 22 year cycle - let alone predictable changes - are highly unlikely.

[ EDIT: it is amusing that 39.37 is approximately the number of inches in a meter: 39.37008 ]

[johnnydeep]

The Sun may be undergoing minimums and maximums (which is caused by its magnetism), but it still darn quiet for a star of its class!

A comparison of the changes in the Sun’s brightness due to sunspots over time (top) to that of a star very much like it (bottom). On average, the Sun changes less than other stars, meaning it’s more quiet magnetically. Credit: MPS / hormesdesign.de

---

Phil Plait of SYFY wrote:

Astronomers have determined that, on average, the Sun is quieter than other stars magnetically, and it's not clear why...

What they found is surprising: The Sun is much quieter than other stars like it! While the Sun's median brightness variation is 0.07%, the other stars had a median of 0.36%, five times higher! That's even twice as much as the Sun's maximum variation of 0.2%.

Ann

What would be the effect to life on Earth if the Sun's activity was more typical? Is this unique quality of the Sun one of the reasons life, as we know it, exists on Earth?

Well, I would think that the largest effect would be an increased number or magnitude of coronal mass ejections (CME's). But from what I understand, CME's, although they can fry power lines and electronics on Earth's surface and in orbit, they would not affect evolving life or even the transient surface environment much. Am I wrong?

[Chris Peterson]

The Sun may be undergoing minimums and maximums (which is caused by its magnetism), but it still darn quiet for a star of its class!

A comparison of the changes in the Sun’s brightness due to sunspots over time (top) to that of a star very much like it (bottom). On average, the Sun changes less than other stars, meaning it’s more quiet magnetically. Credit: MPS / hormesdesign.de

---

Ann

What would be the effect to life on Earth if the Sun's activity was more typical? Is this unique quality of the Sun one of the reasons life, as we know it, exists on Earth?

Well, I would think that the largest effect would be an increased number or magnitude of coronal mass ejections (CME's). But from what I understand, CME's, although they can fry power lines and electronics on Earth's surface and in orbit, they would not affect evolving life or even the transient surface environment much. Am I wrong?

I think in terms of life the most important factors are an increase in charged particles reaching the ground, and the temperature variation created by the greater variation in brightness. A strong magnetic field like our is very protective, but not 100%. If more were thrown our way, more would affect life.

[johnnydeep]

What would be the effect to life on Earth if the Sun's activity was more typical? Is this unique quality of the Sun one of the reasons life, as we know it, exists on Earth?

Well, I would think that the largest effect would be an increased number or magnitude of coronal mass ejections (CME's). But from what I understand, CME's, although they can fry power lines and electronics on Earth's surface and in orbit, they would not affect evolving life or even the transient surface environment much. Am I wrong?

I think in terms of life the most important factors are an increase in charged particles reaching the ground, and the temperature variation created by the greater variation in brightness. A strong magnetic field like our is very protective, but not 100%. If more were thrown our way, more would affect life.

Ok, on the potential DNA disruption - mutations - of more charged particles, but perhaps more mutations could positively affect life by hastening evolution?

As for brightness variation, the example graph is showing less than a 1% variation. Would that really make much of a difference?

[Chris Peterson]

Well, I would think that the largest effect would be an increased number or magnitude of coronal mass ejections (CME's). But from what I understand, CME's, although they can fry power lines and electronics on Earth's surface and in orbit, they would not affect evolving life or even the transient surface environment much. Am I wrong?

I think in terms of life the most important factors are an increase in charged particles reaching the ground, and the temperature variation created by the greater variation in brightness. A strong magnetic field like our is very protective, but not 100%. If more were thrown our way, more would affect life.

Ok, on the potential DNA disruption - mutations - of more charged particles, but perhaps more mutations could positively affect life by hastening evolution?

As for brightness variation, the example graph is showing less than a 1% variation. Would that really make much of a difference?

An increased mutation rate would impact life. Hard to define "better" or "worse" in this context. It's worse if you go extinct, it's better if you're a new species!

A 1% variation is significant enough to have an effect, although it's less than the variation induced by the non-zero eccentricity of our orbit. The real question, I think, isn't what the median values are but what the actual extremes are over millions of years. If these more active stars are transiently a LOT more active, that could be a big deal for life.

[johnnydeep]

I think in terms of life the most important factors are an increase in charged particles reaching the ground, and the temperature variation created by the greater variation in brightness. A strong magnetic field like our is very protective, but not 100%. If more were thrown our way, more would affect life.

Ok, on the potential DNA disruption - mutations - of more charged particles, but perhaps more mutations could positively affect life by hastening evolution?

As for brightness variation, the example graph is showing less than a 1% variation. Would that really make much of a difference?

An increased mutation rate would impact life. Hard to define "better" or "worse" in this context. It's worse if you go extinct, it's better if you're a new species!

A 1% variation is significant enough to have an effect, although it's less than the variation induced by the non-zero eccentricity of our orbit. The real question, I think, isn't what the median values are but what the actual extremes are over millions of years. If these more active stars are transiently a LOT more active, that could be a big deal for life.

Ok, got it - thanks.