A cluster of coronal cells seen by SDO on June 17, 2011. (NASA/SDO AIA instrument)
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There’s something new under the Sun… well, just above the Sun, actually. Scientists at the Naval Research Laboratory have spotted structures in the Sun’s super-hot corona that may shed some light on the way its magnetic fields evolve — especially near the edges of vast, wind-spewing coronal holes.
Coronal holes are regions where the Sun’s magnetic field doesn’t loop back down but rather streams outward into space. Appearing dark in images captured in ultraviolet wavelengths, these holes in the corona allow solar material to flow directly out into the solar system, in many cases doubling the normal rate of the solar wind.
Recently witnessed by NRL researchers using NASA’s SDO and STEREO solar-observing spacecraft, features called coronal cells exist at the boundaries of coronal holes and may be closely associated with their formation and behavior.
The coronal cells are plumes of magnetic activity that stream upward from the Sun, occurring in clusters. Likened to “candles on a birthday cake”, the incredibly hot (1 million K) plumes extend outwards, punching though the lower corona.
Seen near the center of the Sun’s disk, the cells appear structurally similar to granules — short-lived areas of rising and falling solar material on the Sun’s photosphere — but seen from an angle via STEREO, the cells were witnessed to be much larger, elongated and extending higher into the Sun’s atmosphere. For comparison, granules are typically about 1,000 km in diameter while the coronal cells have been measured at 30,000 km across.
“We think the coronal cells look like flames shooting up, like candles on a birthday cake,” said Neil Sheeley, a solar scientist at the Naval Research Laboratory in Washington, D.C. “When you see them from the side, they look like flames. When you look at them straight down they look like cells. And we had a great way of checking this out, because we could look at them from the top and from the side at the same time using observations from SDO, STEREO-A, and STEREO-B.”
Watch a video below of cells made from images acquired by STEREO-B… note how their elongated structure becomes evident as the cells rotate closer to the Sun’s limb.
NRL researchers also noted that the coronal cells appeared when adjacent coronal holes closed and disappeared when the holes opened, suggesting that the holes and cells share the same magnetic structure. In addition, the coronal cells were seen to disappear when a solar filament would erupt nearby, being “extinguished” as the cooler strand of solar material moved across them. Once the filament passed, the cells reformed — again, indicating a direct magnetic association.
The coronal cells were also identified in earlier images from ESA and NASA’s SOHO and Japan’s Hinode spacecraft.
It’s hoped that further study of these candle-like structures will lead to more knowledge of our star’s complex magnetic field and the effects it has on space weather and geomagnetic activity experienced here on Earth.
Read the press release from the Naval Research Laboratory here, and on NASA’s STEREO site here.
Well, not really…… The Sun didn’t do a barrel roll; it was actually the Solar Dynamics Observatory that performed a 360-degree roll about the spacecraft-Sun line. But this video showing the change in perspective of SDO makes it appear as though the Sun suddenly shifted (that’s a new one for 2012 doomsdayers to go crazy over!) This roll maneuver wasn’t just so SDO could have a bit of fun, joyriding out there in its inclined geosynchronous orbit. The roll allows the scientists to remove the instrument optical distortions from the solar images taken by the Helioseismic and Magnetic Imager (HMI) to precisely determine the solar limb. Continue reading “The Sun Does a Barrel Roll”
NASA’s Solar Dynamics Observatory captured this video on March 27 – 28 of two large areas of “dark” plasma on the Sun’s limb, twisting and spiraling in our star’s complex magnetic field. The southern region bears an uncanny resemblance to three figures swaying to some spooky, unheard music… a real “danse macabre” on the Sun!
Spectacular rotation of material from solar prominences and the coronal cavities on September 25, 2011. Credit: NASA/Dr. Xing Li, Dr. Huw Morgan and Mr. Drew Leonard.
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The Solar Dynamics Observatory captured images and video of a spectacular rotation of material from the Sun in a solar prominence. The whirling, dancing prominence created a massive tornado-like feature on the Sun, five times bigger than the Earth. “This is perhaps the first time that such a huge solar tornado is filmed by an imager,” said Dr. Xing Li of Aberystwyth University, presenting his team’s work at the National Astronomy Meeting this week in the UK. “The superb spatial and temporal resolution of SDO allows us to observe the solar atmosphere in great detail.”
The solar tornado was discovered using the Atmospheric Imaging Assembly (AIA) telescope on board SDO. On September 25, 2011, the AIA saw superheated gases as hot as 50,000 – 2,000,000 Kelvin sucked from the origin of a solar prominence, and spiral up into the high atmosphere. It traveled about 200,000 kilometers (124,000 miles) along the Sun for a period of at least three hours.
The hot gases in the tornadoes have speeds as high as 300,000 km per hour (186,000 mph) as opposed to terrestrial tornadoes, which can reach 150 km/h (90 mph).
Li and his team said that these tornadoes often occur at the root of huge coronal mass ejections. The solar tornadoes drag winding magnetic field and electric currents into the high atmosphere. It is possible that the magnetic field and currents play a key role in driving the coronal mass ejections.
A smaller solar tornado was captured in February of 2012:
The recent solar activity did more than spark pretty auroras around the poles. Researchers say the solar storms of March 8th through 10th dumped enough energy in Earth’s upper atmosphere to power every residence in New York City for two years.
Of course, there is no sound in space, but sonfication is a process where any kind of non-auditory data is translated as sound. “We’re transforming space data into the sonic realm such that we can gain a new perspective, and begin to ask new questions,” said Robert Alexander, a doctoral student at the University of Michigan, getting his Ph.D in Design Science, who created this great sonification video of the recent solar storm activity. Alexander used data from two spacecraft: SOHO, studying the Sun, and the MESSENGER spacecraft at Mercury, which has the University of Michigan’s Fast Imaging Plasma Spectrometer (FIPS) on board, an imaging mass spectrometer.
Mercury was recently bombarded with a solar storm, and the sound created from particles colliding with the FIPS is utterly horrifying, sounding like the worst monster you could ever imagine. Continue reading “What Does a Solar Storm Sound Like?”
A mosaic of 4 images taken of the Sun on Nov. 13, 2011. Credit: Leonard Mercer.
The rotation of the Sun is kind of hard to pin down. That’s because a day on the Sun depends on which part of the Sun you’re talking about. Confused yet? It kept astronomers puzzled for years too. Let’s look at how the rotation of the Sun changes.
A spot on the equator of the Sun takes 24.47 days to rotate around the Sun and return to the same position. Astronomers call this sidereal rotation period, which is different from the synodic period – the amount of time it takes for a spot on the Sun to rotate back to face the Earth. But the Sun’s rotation rate decreases as you approach the poles, so it can actually take 38 days for regions around the poles to rotate once.
The Sun’s rotation is seen by observing sunspots. All sunspots move across the face of the Sun. This motion is part of the general rotation of the Sun on its axis. Observations also indicate that the Sun does not rotate as a solid body, but it spins differentially. That means that it rotates faster at the equator of the Sun and slower at its poles. The gas giants Jupiter and Saturn also have differential rotation.
And so, astronomers have decided to measure the rotation rate of the Sun from an arbitrary position of 26° from the equator; approximately the point where we see most of the sunspots. At this point, it takes 25.38 days to rotate and return to the same spot in space.
Astronomers also know that the interior of the Sun rotated differently than the surface. The inner regions, the core and the radiative zone, rotate together like a solid body. And then the outer layers, the convective zone and photosphere, rotate at a different speed.
The Sun and the entire solar system orbits around the center of the Milky Way galaxy. The average velocity of the solar system is 828,000 km/hr. At that rate it will take about 230 million years to make one complete orbit around the galaxy. The Milky Way is a spiral galaxy. It is believed that it consists of a central bulge, 4 major arms, and several shorter arm segments. The Sun and the rest of our solar system is located near the Orion arm, between two major arms, Perseus and Sagittarius. The diameter of the Milky Way is about 100,000 light years and the Sun is located about 28,000 light-years from the Galactic Center. It has been suggested fairly recently that ours is actually a barred spiral galaxy. That means that instead of a bulge of gas and stars at the center, there is probably a bar of stars crossing the central bulge.
So when someone asks you what the rotation of the Sun is, ask them which part.
Here’s an article from Universe Today about the Sun’s magnetic field flip, and here’s an article about how there were no sunspots on the surface of the Sun.
SDO AIA 211 image showing a large triangular hole in the Sun's corona on March 13
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An enormous triangular hole in the Sun’s corona was captured earlier today by NASA’s Solar Dynamics Observatory, seen above from the AIA 211 imaging assembly. This gap in the Sun’s atmosphere is allowing more charged solar particles to stream out into the Solar System… and toward Earth as well.
Normally, loops of magnetic energy keep much of the Sun’s outward flow of gas contained. Coronal holes are regions — sometimes very large regions, such as the one witnessed today — where the magnetic fields don’t loop back onto the Sun but instead stream outwards, creating channels for solar material to escape.
The material constantly flowing outward is called the solar wind, which typically “blows” at around 250 miles (400 km) per second. When a coronal hole is present, though, the wind speed can double to nearly 500 miles (800 km) per second.
Increased geomagnetic activity and even geomagnetic storms may occur once the gustier solar wind reaches Earth, possibly within two to three days.
The holes appear dark in SDO images because they are cooler than the rest of the corona, which is extremely hot — around 1,000,000 C (1,800,000 F)!
Here’s another image, this one in another AIA channel (193):
[/caption] Mass: 1.98892 x 1030 kg Diameter: 1,391,000 kilometers Radius: 695,500 km Surface gravity of the Sun: 27.94 g Volume of the Sun: 1.412 x 1018 km3 Density of the Sun: 1.622 x 105 kg/m3
How Big is the Sun?
The Sun is the largest object in the Solar System, accounting for 99.86% of the mass.
As stars go, the Sun is actually a medium-sized, and even smallish star. Stars with much more mass can be much larger than the Sun. For example, the red giant Betelgeuse, in the constellation of Orion is thought to be 1,000 times larger than the Sun. And the largest known star is VY Canis Majoris, measuring approximately 2,000 times larger than the Sun. If you could put VY Canis Majoris into our Solar System, it would stretch out past the orbit of Saturn.
The size of the Sun is changing. In the future when it runs out of usable hydrogen fuel in the core, it will become a red giant as well. It will engulf the orbits of Mercury and Venus, and possibly even the orbit of the Earth. For a few million years, the Sun will be about 200 times bigger than its current size.
After the Sun becomes a red giant, it will shrink down to become a white dwarf star. Then the size of the Sun will only be roughly the size of the Earth.
Mass of the Sun
The mass of the Sun is 1.98892 x 1030 kilograms. That’s a really big number, and it’s really hard to put it into context, so let’s write out the mass of the Sun, with all the zeros.
Still need to wrap your head around this? Let’s give you some comparisons. The mass of the Sun is 333,000 times the mass of the Earth. It’s 1,048 times the mass of Jupiter, and 3,498 times the mass of Saturn.
In fact, the Sun accounts for 99.8% of all the mass in the entire Solar System; and most of that non-Sun mass is Jupiter and Saturn. To say that the Earth is an insignificant speck is an understatement.
When astronomers try to gauge the mass of another star-like object, they use the mass of the Sun for comparison. This is known as a “solar mass”. So the mass of objects, like black holes, will be measured in solar masses. A massive star might have 5-10 solar masses. A supermassive black hole could have hundreds of millions of solar masses.
Astronomers will refer to this with an M beside a symbol that looks like a circle with a dot in the middle – M⊙. To show a star that has 5 times the mass of the Sun, or 5 solar masses, it would be 5 M⊙. Eta Carinae, one of the most massive stars known. Image credit: NASA
The Sun is massive, but it’s not the most massive star out there. In fact, the most massive star we know of is Eta Carinae, which has a mass of 150 times the mass of the Sun.
The Sun’s mass is actually slowly decreasing over time. There are two processes at work here. The first is the fusion reactions in the core of the Sun, converting atoms of hydrogen into helium. Some of the Sun’s mass is lost through the fusion process, as atoms of hydrogen are converted into energy. The warmth we feel from the Sun, is the Sun’s lost mass. The second way is the solar wind, which is constantly blowing protons and electrons into outer space.
Mass of the Sun in kilograms: 1.98892 x 1030 kg
Mass of the Sun in pounds: 4.38481 x 1030 pounds
Mass of the Sun in tons: 2.1924 x 1027 tons
Diameter of the Sun
The diameter of the Sun is 1.391 million kilometers or 870,000 miles.
Again, let’s put this number into perspective. The diameter of the Sun is 109 times the diameter of the Earth. It’s 9.7 times the diameter of Jupiter. Really, really big.
Pardon the pun, but the Sun doesn’t hold a candle to some of the largest stars in the Universe. The biggest star we know of is called VY Canis Majoris, and astronomers think it could be 2,100 times the diameter of the Sun. The Earth compared to Sunspot 1312 on 10-10-11. Credit: Ron Cottrell.
Diameter of the Sun in kilometers: 1,391,000 km
Diameter of the Sun in miles: 864,000 miles
Diameter of the Sun in meters: 1,391,000,000 meters
Diameter of the Sun compared to Earth: 109 Earths
Radius of the Sun
The radius of the Sun, the measurement from the exact center of the Sun out to its surface, is 695,500 kilometers.
This radius is essentially the same however you measure it, from the center to the equator, or the from the center to the Sun’s poles. But you need to be careful with other objects, however, because the speed of their rotation affects the radius.
The Sun takes about 25 days to turn once on its axis. Because it rotates relatively slowly, the Sun doesn’t flatten out at all. The distance from the center to the poles is almost exactly the same as the distance from the center to the equator.
There are stars out there which are dramatically different, though. For example, the star Achernar, located in the constellation Eridanus, is flattened by 50%. In other words, the distance from the poles is half the distance across the equator. In this situation, the star actually looks like spinning-top toy.
So, relative to out stars out there, the Sun is almost a perfect sphere.
Astronomers use the Sun’s radius, or “solar radius” to compare the sizes of stars and other celestial bodies. For example, a star with 2 solar radii is twice as large as the Sun. A star with 10 solar radii is 10x as large as the Sun, and so on. VY Canis Majoris. The biggest known star.
Polaris, the North Star, is the brightest star in the constellation Ursa Minor (Little Dipper) and, because of its proximity to the north celestial pole, is considered the current northern pole star. Polaris is primarily used for navigation and has a solar radius of 30. That means, it is 30 times bigger than the Sun.
Sirius which is the brightest star in the night sky. In terms of apparent magnitude, the second brightest star, Canopus, has only half that of Sirius’. No wonder it really stands out. Sirius is actually a binary star system, with Sirius A having a solar radius of 1.711 and B, which is much smaller, at about 0.0084.
Radius of the Sun in kilometers: 695,500 km
Radius of the Sun in miles: 432,200 miles
Radius of the Sun in meters: 695,500,000 meters
Radius of the Sun compared to Earth: 109 Earths
Gravity of the Sun
The Sun has an enormous amount of mass, and so it has a lot of gravity. In fact, the mass of the Sun is 333,000 times more than the mass of the Earth. Forget that the surface temperature of the Sun is 5,800 Kelvin and made of hydrogen – what would you feel if you could walk on the surface of the Sun? Think about this, the gravity of the Sun at the surface is 28 times the gravity of the Earth.
In other words, if your scale says 100 kg on Earth, it would measure 2,800 kg if you tried to walk on the surface of the Sun. Needless to say, you would die pretty quickly just from the pull of gravity, not to mention the heat, etc.
The Sun’s gravity pulls all of its mass (mostly hydrogen and helium) into an almost perfect sphere. Down at the core of the Sun, the temperatures and pressures are so high that fusion reactions are possible. The tremendous amount of light and energy pouring out of the Sun counteracts the pull of gravity trying to collapse it down. The layout of the solar system, including the Oort Cloud, on a logarithmic scale. Credit: NASA
Astronomers define the Solar System as the distance under the influence of gravity from the Sun. We know that the Sun holds distant Pluto in orbit (5.9 billion km away on average). But astronomers think that the Oort Cloud extends out to a distance of 50,000 astronomical units (1 AU is the distance from the Earth to the Sun), or 1 light-year. In fact, the influence of the Sun’s gravity could extend out to 2 light-years away, the point at which the pull from other stars is stronger.
Surface gravity of the Sun: 27.94 g
Density of the Sun
The density of the Sun is 1.4 grams per cubic centimeter. Just to give you a comparison, the density of water is 1 g/cm3. In other words, if you could find a pool large enough, the Sun would sink down and not float. And this seems kind of counter-intuitive. Isn’t the Sun made of hydrogen and helium, the two lightest elements in the Universe? So how can the density of the Sun be so high?
Well, it all comes down to gravity. But first, let’s calculate the density of the Sun for ourselves.
Formula for density is to divide mass by volume. The mass of the Sun is 2 x 1033 grams, and the volume is 1.41 x 1033 cm3. And so, if you do the math, the density of the Sun works out to be 1.4 g/cm3. Interior of the Sun. Image credit: NASA
The Sun holds itself together with gravity. Although the outermost layers of the Sun might be less dense, the intense gravity crushes the inner regions to enormous pressures. At the core of the Sun, the pressure is more than 1 million metric tons/cm sq – that’s equivalent to more than 10 billion times the atmosphere of the Earth. And once you get those kinds of pressures, fusion can ignite.
Density of the Sun: 1.622 x 105 kg/m3
Volume of the Sun
The volume of the Sun is 1.412 x 1018 km3. That’s a lot of cubic kilometers. Do you need something to compare this with? The volume of the Sun is so great that it would take 1.3 million planets the size of the Earth to fill it up. Or you could fill it with almost 1000 planets the size of Jupiter.
Volume of the Sun in cubic kilometers: 1.412 x 1018 km3
Volume of the Sun compared to Earth: 1,300,000
Circumference of the Sun
The circumference of the Sun is 4,379,000 km.
Just for comparison, the equatorial circumference of the Earth is 40,075 km. So, the circumference of the Sun is 109 times larger than the circumference of the Earth. And the circumference of the Sun is 9.7 times bigger than the circumference of Jupiter.
Even though the CME unleashed by active region 1429 initially hit Earth a bit softer than expected yesterday (read why here), it ended up gaining some extra “oomph” once the magnetic fields lined up right… enough to ignite some amazing displays of aurorae like the one shown above over Iceland, photographed by Jónína Óskarsdóttir!
And that wasn’t the last we’d hear from AR1429 either; at around 10:30 pm EST on March 8, the region lit up again with an M6.3 flare… although smaller than the previous X5.4-class flare, it produced a temporary radio blackout and released another Earth-directed CME, which is expected to arrive in the coming hours.
Dr. Alex Young, solar physicist at NASA’s Goddard Space Flight Center, reported this morning on his blog The Sun Today:
The flare produced a temporary radio blackout as well as a possible Earth directed CME. We will have to wait and see. The sunspot group still shows potential for more activity as the region sits near the central meridian of the Sun. Facing directly at Earth this is a prime location to produce more geo-effective solar activity.
Here is a look at the flare captured by the 131 Angstrom wavelength camera on the Solar Dynamics Observatory (SDO). This shows us the super hot 5-10 million degree plasma produced by the solar flare.
M6.3-class flare from AR1429. (NASA/SDO/AIA team)
Dr. Young also noted that bright aurorae could be visible in lower latitudes as a result of the latest CME, expected to impact Earth at 1:50 am EST:
Aurora watchers at higher latitudes such as the northern US should keep their eyes out in the early morning and maybe even into tonight depending upon how this storm progresses.
Many times the size of Earth, active region 1429 has been the source of at least five significant flares over the past week. As it moves across the face of the Sun, its shape has become more and more complex — a sure sign, notes Dr. Young, that magnetic forces within it are twisting further and further towards a breaking point. And when they snap, there’s a flare.
“It’s interesting, they kind of look like a mole,” Dr. Young said during an interview on March 8. “And when you monitor a mole, they tell you as long as it stays in a nice symmetric shape and it doesn’t become really complicated and complex, it’s okay. It’s the same sort of thing with sunspots… when they become complicated and twisted, then that mean the magnetic fields inside of them have become more twisted, like a rubber band twisting around until little knots pop up in it. And right now we have been monitoring that sunspot and it is getting more complex.”
As far as the effects we see here on Earth are concerned, that’s all about the resulting CME — the enormous cloud of charged solar particles that gets blown out into the Solar System. If that cloud impacts Earth’s magnetic field, and if the direction of the cloud happens to be opposite the direction that Earth’s magnetic field is pointed, a lot of energy is “pumped into” our magnetosphere, resulting in a geomagnetic storm.
AR1429 (NASA/SDO/HMI Intensitygram)
During yesterday’s CME impact the Earth’s magnetic field was pointed north — the same direction as the CME. As a result much of the solar material simply flowed along and over it. But the wake ended up getting caught up in the south-directed part of the field, ramping up the energy index (measured as Kp) as the hours progressed. As yet there’s no way to know for certain how a particular CME will align with Earth’s magnetic field.
According to physicist Dr. Philip Scherrer of Stanford University, “we still need better — or perhaps faster — models” to be able to accurately predict the orientation of incoming CMEs. “We are perhaps a few years of research away from completing the picture.”
Currently the geomagnetic storm level is at G3, which according to the NOAA’s Space Weather Scale could result in voltage problems on power systems, increased drag on satellites and “intermittent satellite navigation and low-frequency radio navigation problems… and aurora has been seen as low as Illinois and Oregon.”
So keep an eye out for northern lights in tonight’s skies, and stay tuned for more updates!
Thanks to Dr. Alex Young for the information! You can follow him on Facebook and Twitter and on his personal blog The Sun Today. Also thanks to Dr. Phil Scherrer at Stanford University and SpaceWeather.com for the heads-up on Jónína’s photo. See more of her aurora photography here. (Used with permission.)
