A pioneering method suggests that the size of our Sun and the solar radius may be due revision.
Our host star is full of surprises. Studying our Sun is the most essential facet of modern astronomy: not only does Sol provide us with the only example of a star we can study up close, but the energy it provides fuels life on Earth, and the space weather it produces impacts our modern technological civilization.
Now, a new study, titled The Acoustic Size of the Sunsuggests that a key parameter in modern astronomy and heliophysics—the diameter of the Sun—may need a slight tweak.
Using ground-based and space-based observations, a team of researchers has been monitoring a difficult-to-see comet carefully. It’s called Comet 323P/SOHO, and it was discovered over 20 years ago in 1999. But it’s difficult to observe due to its proximity to the Sun.
They’ve found that the Sun is slowly tearing the comet to pieces.
Solar flares are complex phenomena. They involve plasma, electromagnetic radiation across all wavelengths, activity in the Sun’s atmosphere layers, and particles travelling at near light speed. Spacecraft like NASA’s Solar and Heliophysics Observatory (SOHO) and the Parker Solar Probe shed new light on the Sun’s solar flares.
But it was a Japanese-led mission called Yohkoh that spotted an unusual solar flare in 1999. This flare displayed a downward flowing motion toward the Sun along with the normal outward flow. What caused it?
A team of researchers think they’ve figured it out.
For a quarter of a century, the ESA-NASA Solar and Heliospheric Observatory (SOHO) has been essential in helping scientists understand the heart of our Solar System, the Sun. The SOHO mission launched 25 years ago this week, and to celebrate, ESA compiled a wonderful mosaic of images, and NASA put together a remarkable SOHO “greatest hits” timelapse video.
Strictly speaking, there aren’t strict boundaries between Earth and space. Our atmosphere doesn’t just end at a certain altitude; it peters out gradually. A new study from Russia’s Space Research Institute (SRI) shows that our atmosphere extends out to 630,000 km into space.
The Solar and Heliospheric Observatory (SOHO) is celebrating 22 years of observing the Sun, marking one complete solar magnetic cycle in the life of our star. SOHO is a joint project between NASA and the ESA and its mission is to study the internal structure of the sun, its extensive outer atmosphere, and the origin of the solar wind.
The activity cycle in the life of the Sun is based on the increase and decrease of sunspots. We’ve been watching this activity for about 250 years, but SOHO has taken that observing to a whole new level.
Though sunspot cycles work on an 11-year period, they’re caused by deeper magnetic changes in the Sun. Over the course of 22 years, the Sun’s polarity gradually shifts. At the 11 year mark, the orientation of the Sun’s magnetic field flips between the northern and southern hemispheres. At the end of the 22 year cycle, the field has shifted back to its original orientation. SOHO has now watched that cycle in its entirety.
SOHO is a real success story. It was launched in 1995 and was designed to operate until 1998. But it’s been so successful that its mission has been prolonged and extended several times.
SOHO’s 22 years of observation has turbo-charged our space weather forecasting ability. Space weather is heavily influenced by solar activity, mostly in the form of Coronal Mass Ejections (CMEs). SOHO has observed well over 20,000 of these CMEs.
Space weather affects key aspects of our modern technological world. Space-based telecommunications, broadcasting, weather services and navigation are all affected by space weather. So are things like power distribution and terrestrial communications, especially at northern latitudes. Solar weather can also degrade not only the performance, but the lifespan, of communication satellites.
Besides improving our ability to forecast space weather, SOHO has made other important discoveries. After 40 years of searching, it was SOHO that finally found evidence of seismic waves in the Sun. Called g-modes, these waves revealed that the core of the Sun is rotating 4 times faster than the surface. When this discovery came to light, Bernhard Fleck, ESA SOHO project scientist said, “This is certainly the biggest result of SOHO in the last decade, and one of SOHO’s all-time top discoveries.”
SOHO also has a front row seat for comet viewing. The observatory has witnessed over 3,000 comets as they’ve sped past the Sun. Though this was never part of SOHO’s mandate, its exceptional view of the Sun and its surroundings allows it to excel at comet-finding. It’s especially good at finding sun-grazer comets because it’s so close to the Sun.
“But nobody dreamed we’d approach 200 (comets) a year.” – Joe Gurman, mission scientist for SOHO.
“SOHO has a view of about 12-and-a-half million miles beyond the sun,” said Joe Gurman in 2015, mission scientist for SOHO at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “So we expected it might from time to time see a bright comet near the sun. But nobody dreamed we’d approach 200 a year.”
A front-row seat for sun-grazing comets allows SOHO to observe other aspects of the Sun’s surface. Comets are primitive relics of the early Solar System, and observing them with SOHO can tell scientists quite a bit about where they formed. If a comet has made other trips around the Sun, then scientists can learn something about the far-flung regions of the Solar System that they’ve traveled through.
Watching these sun-grazers as they pass close to the Sun also teaches scientists about the Sun. The ionized gas in their tails can illuminate the magnetic fields around the Sun. They’re like tracers that help observers watch these invisible magnetic fields. Sometimes, the magnetic fields have torn off these tails of ionized gas, and scientists have been able to watch these tails get blown around in the solar wind. This gives them an unprecedented view of the details in the movement of the wind itself.
SOHO is still going strong, and keeping an eye on the Sun from its location about 1.5 million km from Earth. There, it travels in a halo orbit around LaGrange point 1. (It’s orbit is adjusted so that it can communicate clearly with Earth without interference from the Sun.)
Beyond the important science that SOHO provides, it’s also a source of amazing images. There’s a whole gallery of images here, and a selection of videos here.
You can also check out daily views of the Sun from SOHO here.
Over the course of April 28–29 a gigantic filament, briefly suspended above the surface* of the Sun, broke off and created an enormous snakelike eruption of plasma that extended millions of miles out into space. The event was both powerful and beautiful, another demonstration of the incredible energy and activity of our home star…and it was all captured on camera by two of our finest Sun-watching spacecraft.
Watch a video of the event below.
Made from data acquired by both NASA’s Solar Dynamics Observatory (SDO) and the joint ESA/NASA SOHO spacecraft, the video was compiled by astronomer and sungrazing comet specialist Karl Battams. It shows views of the huge filament before and after detaching from the Sun, and gives a sense of the enormous scale of the event.
At one point the plasma eruption spanned a distance over 33 times farther than the Moon is from Earth!
Filaments are long channels of solar material contained by magnetic fields that have risen up from within the Sun. They are relatively cooler than the visible face of the Sun behind them so they appear dark when silhouetted against it; when seen rising from the Sun’s limb they look bright and are called prominences.
When the magnetic field lines break apart, much of the material contained within the filaments gets flung out into space (a.k.a. a CME) while some gets pulled back down into the Sun. These events are fairly common but that doesn’t make them any less spectacular!
Like coins, most comet have both heads and tails. Occasionally, during a close passage of the Sun, a comet’s head will be greatly diminished yet still retain a classic cometary outline. Rarely are we left with nothing but a tail. How eerie it looks. Like a feather plucked from some cosmic deity floating down from the sky. Welcome to C/2015 D1 SOHO, the comet that almost didn’t make it.
It was discovered on Feb. 18 by Thai amateur astronomer and writer Worachate Boonplod from the comfort of his office while examining photographs taken with the coronagraph on the orbiting Solar and Heliospheric Observatory (SOHO). A coronagraph blocks the fantastically bright Sun with an opaque disk, allowing researchers to study the solar corona as well as the space near the Sun. Boonplod regularly examines real-time SOHO images for comets and has a knack for spotting them; in 2014 alone he discovered or co-discovered 35 comets without so much as putting on a coat.
Learn why there are so many sungrazing comets
Most of them belong to a group called Kreutz sungrazers, the remains of a much larger comet that broke to pieces in the distant past. The vast majority of the sungrazers fritter away to nothing as they’re pounded by the Sun’s gravity and vaporize in its heat. D1 SOHO turned out to be something different – a non-group comet belonging to neither the Kreutz family nor any other known family.
After a perilously close journey only 2.6 million miles from the Sun’s 10,000° surface, D1 SOHO somehow emerged with two thumbs up en route to the evening sky. After an orbit was determined, we published a sky map here at Universe Today encouraging observers to see if and when the comet might first become visible. Although it was last seen at around magnitude +4.5 on Feb. 21 by SOHO, hopes were high the comet might remain bright enough to see with amateur telescopes.
On Wednesday evening Feb. 25, Justin Cowart, a geologist and amateur astronomer from Alto Pass, Illinois figured he’d have a crack at it. Cowart didn’t have much hope after hearing the news that the comet may very well have crumbled apart after the manner of that most famous of disintegrators, Comet ISON . ISON fragmented even before perihelion in late 2013, leaving behind an expanding cloud of exceedingly faint dust.
Cowart set up a camera and tracking mount anyway and waited for clearing in the west after sunset. Comet D1 SOHO was located some 10° above the horizon near the star Theta Piscium in a bright sky. Justin aimed and shot:
“I was able to see stars down to about 6th magnitude in the raw frames, but no comet,” wrote Cowart. “I decided to stack my frames and see if I could do some heavy processing to bring out a faint fuzzy. To my surprise, when DeepSkyStacker spit out the final image I could see a faint cloud near Theta Picsium, right about where the comet expected to be!”
Cowart sent the picture off to astronomer Karl Battams, who maintains the Sungrazer Project website, for his opinion. Battams was optimistic but felt additional confirmation was necessary. Meanwhile, comet observer José Chambogot involved in the discussion and plotted D1’s position on a star atlas (in the blinking photo above) based on a recent orbit calculation. Bingo! The fuzzy streak in Justin’s photo matched the predicted position, making it the first ground-based observation of the new visitor.
Comet D1 SOHO’s orbit is steeply inclined (70°) to the Earth’s orbit. After rounding the Sun, it turned sharply north and now rises higher in the western sky with each passing night for northern hemisphere skywatchers. Pity that the Moon has been a harsh mistress, washing out the sky just as the comet is beginning to gain altitude. These less-than-ideal circumstances haven’t prevented other astrophotographers from capturing the rare sight of a tailless comet. On Feb. 2, Jost Jahn of Amrum, Germany took an even clearer image, confirming Cowart’s results.
To date, there have been no visual observations of D1 SOHO made with binoculars or telescopes, so it’s difficult to say exactly how bright it is. Perhaps magnitude +10? Low altitude, twilight and moonlight as well as the comet’s diffuse appearance have conspired to make it a lofty challenge. That will change soon.
Once the Moon begins its departure from the evening sky on March 6-7, a window of darkness will open. Fortuitously, D1 SOHO will be even higher up and set well after twilight ends. I’m as eager as many of you are to train my scope in its direction and bid both hello and farewell to a comet we’ll never see again.
Here are fresh maps based on the most recent orbit published by the Minor Planet Center. Assuming you wait until after Full Moon, start looking for the comet in big binoculars or a moderate to large telescope right at the end of evening twilight when it’s highest in a dark sky. The comet sets two hours after the end of twilight on March 7th from the central U.S.
A newly-discovered comet may soon become bright enough to see from a sky near you. Originally dubbed SOHO-2875, it was spotted in photos taken by the Solar and Heliospheric Observatory(SOHO) earlier this week. Astronomer Karl Battams, who maintains the Sungrazer Project website, originally thought this little comet would dissipate after its close brush with the Sun. To his surprise, it outperformed expectations and may survive long enough to see in the evening sky.
Most sungrazing comets discovered by SOHO are members of the Kreutz family, a group of icy fragments left over from the breakup of a single much larger comet centuries ago. We know they’re all family by their similar orbits. The newcomer, SOHO’s 2,875th comet discovery, is a “non-group” comet or one that’s unrelated to the Kreutz family or any other comet club for that matter. According to Battams these mavericks appear several times a year. As of today (Feb. 24) its official name is C/2015 D1 (SOHO).
What’s unusual about #2,875 is how bright it is. At least for now, it appears to have survived the Sun’s heat and gravitational tides and is turning around to the east headed for the evening sky. Before it left SOHO’s field of view on Feb. 21, the comet was still around magnitude +4-4.5.
No one can say for sure whether it has what it takes to hang on, so don’t get your hopes up just yet. Battams and others carefully calculated the comet’s changing position in the SOHO images and sent the data off to the Minor Planet Center, which today published an orbit.
Based on this preliminary orbit, I’ve plotted SOHO-2875’s path for the next couple weeks as it tracks up through Pisces and Pegasus during the early evening hours. Given that it’s probably no brighter than magnitude +6 at the moment and very low in the west at dusk, it may still be swamped in twilight’s glow.
Barring an unexpected outburst, there’s no question that the comet will fade in the coming days as its distance from both the Earth and Sun increase. Right now it’s 79 million miles from us and 28 million miles from the Sun. That puts it about 8 million miles closer to the Sun than the planet Mercury.
I drew up the chart for about 75 minutes after sunset in late twilight. Keep in mind that since the comet’s positions were determined via spacecraft imagery, which isn’t as precise as photographing it from ground observatories, its orbit is preliminary. That means it may not be on the precise path shown on the map. Be sure you search up-down and right-left of the plotted locations.
It’s also very possible the comet is in the process of disintegration after perihelion passage, so it may not be a dense, compact object but rather a diffuse cloud of glowing dust. Will it go the way of Comet ISON and fade away to nothing? Who knows? I sure don’t but can’t wait to find out what it’s up to the next clear night.
BTW, if you’ve got a software program that downloads orbital elements for comets to create your own charts, you’ll find the numbers you need in today’s Minor Planet Circular. Be sure to use the “post-perihelion” elements that predict the comet’s location from here on out.
Last year’s Thanksgiving adventure for astronomers happened when Comet ISON passed within 1.2 million kilometres (750,000 miles) of the Sun. While many people were hoping the comet would stick around and produce a good show, the comet disintegrated despite a brief flare-up shortly after passing perihelion.
Scientists have just modelled the production of dust on the comet and concluded there was a “violent outburst” that happened 8.5 hours before closest approach, when the comet spewed out 11,500 tonnes (12,765 tons) of material.
“It is most likely that the final break-up of the nucleus triggered this eruption, abruptly releasing gas and dust trapped inside the nucleus,” stated Werner Curdt from the Max Planck Institute of Solar System Research, who was the lead researcher on the project. “Within a few hours the dust production stopped completely.”
Because the last few parts of the comet’s encounter were obscured by an occulting disk on the Large Angle and Spectrometric Coronagraph on the Solar and Heliospheric Observatory (SOHO), astronomers decided to model the encounter based on other data they gathered before and after.
They did have one source of data, which was another instrument called the Solar Ultraviolet Measurements of Emitted Radiation (SUMER). It’s usually used to investigate plasma activity on the sun and not faint comets, but the scientists felt it could be repurposed. T
hey switched modes on the instrument and captured the tail in far ultraviolet light, light “emitted from the solar disc and reflected by the dust particles into space,” the European Space Agency stated.
Then they compared what they saw with computer simulations, coming up with the dust estimations.