A Big Hole in the Sun’s Atmosphere

Dec. 6, 2018:  A large hole in the sun’s atmosphere is facing Earth and spewing a stream of solar wind in our direction. NASA’s Solar Dynamics Observatory is monitoring the structure, shown here in a false-color UV image taken on Dec. 6th:

The hole (technical term: “coronal hole”) is so large it almost completely bisects the solar disk, stretching more than a million km across the sun’s equator.

We’ve seen this coronal hole before. It has been spinning around with the sun, lashing Earth with solar wind approximately once a month since September. Last month, the lashing commenced on Nov. 9th, lasted for almost 3 days, and caused sharp tremors in the geomagnetic field. Solar winds blowing faster than 600 km/s sparked an explosion of Phoenix-shaped auroras over Norway:

“The display over Senja, Norway, on Nov. 11th was nothing short of magical,” recalls photographer Adrien Mauduit. “Huge colorful pillars took the shape of a fiery bird.”

The same stream of solar wind will return on Dec. 8th or 9th and it may be even more potent this time because the underlying coronal hole has hrown larger in the intervening month. Arctic sky watchers, mark your calendars and warm your cameras. The Phoenix might rise again. Free: Aurora Alerts.

Realtime Aurora Photo Gallery

ZEN ASTRONAUT: Are the holidays stressing you out? Get your zen from the edge of space. On Dec. 2, 2018, the students of Earth to Sky Calculus launched a cosmic ray balloon to the stratosphere. This meditating spaceman pendant went along for the ride:

The students are selling the pendants to support their ballooning program. You can have one for $129.95. They make great gifts for space fans and are guaranteed to soothe holiday stress. Each premium stainless steel pendant comes with a greeting card showing the astronaut in flight and telling the story of its journey to the edge of space and back again.

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A Comet as Big as the Full Moon

Dec. 4, 2018: On Dec. 16th, Comet 46P/Wirtanen will approach Earth less than 11.5 million km away–making it one of the 10 closest-approaching comets of the Space Age. It’s a small comet, with a nucleus barely 1 km wide, but such proximity makes even a small things appear large. The comet’s gaseous atmosphere is now as wide as a full Moon. Mike Broussard of Perry, Louisiana, photographed the comet on Dec. 2nd and inserted the Moon for scale:

“The comet still has a couple of weeks before closest approach and it is already as big as a full Moon,” says Broussard, who could see the comet with his naked eye–“just barely using averted vision and only when it was in the darkest section of the sky,” he adds.

Despite its close approach, 46P/Wirtanen will never become a Great Comet like Comet Hayakutake in 1996 or Comet Hale-Bopp in 1997. Wirtanen’s relatively small core of dirty ice cannot produce enough gas and dust to create a really bright, flamboyant tail. The best case scenario is probably a big diffuse cloud of magnitude +3 or +4, barely visible to the unaided eye but an easy target for binoculars and small wide-field telescopes.

Last night in Cape Cod, Massachusetts, photographer Chris Cook didn’t even need a telescope to capture Wirtanen’s green glow. He took this picture using a Canon 6D digital camera with a 35 mm lens:

“This was my first sighting of Comet 46P/Wirtanen–just under naked eye visibility for my skies, but in 7×50 binoculars I could see a very large coma (ball of gas) almost 1° in diameter!” reports Cook. “It reminds me of Comet Hayakutake’s massive coma but not nearly as bright.”

Celebrated astrophotographer Juan Carlos Casado, who last night took his own HDR image of the comet above a church tower in Spain, offers some advice to novices: “Use Raw file format, a fast lens (at least f/2.8) and ISO settings between 1600 and 3200. The exposure will depend on the focal length. I normally use the 500 rule–that is, exposure = 500 / focal (mm) with a tripod. It also helps in areas with light pollution to use an antipollution filter. I am now using Optolong L-Pro clip filter which gives excellent color balance.”

On the nights of closest approach, 46P/Wirtanen can be found in the constellation Taurus rising in the east at sunset and high in the sky at midnight. Sky watchers in the northern hemisphere may orient themselves using these sky maps: Dec. 5, Dec. 6, Dec. 7, Dec. 8, Dec. 9, Dec. 10, Dec. 11, Dec. 12, Dec. 13, Dec. 14, Dec. 15, Dec. 16

More resources: orbital elements; ephemeris; 3D orbit; light curve.

Hyperactive Comet Approaches Earth

Nov. 26, 2018: Small but hyperactive Comet 46P/Wirtanen is approaching Earth and could soon become visible to the naked eye. On Dec. 16th, the kilometer-wide ball of dirty ice will be less than 11.5 million km away–making it one of the 10 closest-approaching comets of the Space Age. It already looks magnificent through amateur telescopes. On Nov. 26th, Gerald Rhemann took this picture using a 12-inch reflector in Farm Tivoli, Namibia:

“The comet is currently gliding through the southern constellation Fornax,” says Rhemann. “If you look carefully at the image, you can see galaxy NGC 922 near the comet’s head, and another galaxy ESO 479-2 on the left.”

Rhemann says that the comet’s emerald green atmosphere is 50 arcminutes wide. In other words–almost twice as wide as a full Moon. Its apparent diameter could double in the weeks ahead as the comet comes even closer. Because Wirtanen’s brightness is spread over such a wide area, it is diluted just below the limit of naked eye visibility, with a current magnitude near +6.0. We don’t yet know if the comet will ultimately become visible to the unaided eye–but it will certainly be an easy target for binoculars and backyard telescopes in December.

The nucleus of 46P/Wirtanen is small (~1 km) compared to greater comets such as Hale-Bopp (~30 km) and Halley (~15 km). It makes up for this deficit by hyperactivity. Recent measurements show that the core of 46P/Wirtanen is spinning once every 8.9 hours and spewing almost 1028 water molecules every second. This exceeds the expected production of such a small comet.

Comet Wirtanen passes through the inner solar system every 5.4 years. Right now it is just below the orbit of Earth, and the gap is narrowing. Click on the image above to explore the comet’s approach, courtesy of NASA/JPL.

More resources: sky map; ephemeris; 3D orbit; light curve.

Realtime Comet Photo Gallery

Martian Cubesats to Broadcast Mars Landing

Nov. 25, 2018: For the first time ever, cubesats are approaching Mars. Their mission: To experience 7 minutes of terror. If all goes as planned, on Monday the two tiny spacecraft will watch NASA’s InSight lander touchdown on the Red Planet, relaying updates to Earth in near-real time.

PIA22316_hires_crop

InSight is the latest NASA probe to land on Mars–or disintegrate in the attempt. On Nov. 26th, it will tear through the planet’s atmosphere in a fireball, shedding more than 12,000 mph of velocity in just under 7 minutes. NASA hopes InSight will touchdown gently on the plains of Elysium Planitia where it can drill into Mars, using seismometers, heat flow sensors, and radios to study the planet’s interior.

Officially the two cubesats are known as MarCO-A and MarCO-B, but JPL engineers have nicknamed them “WALL-E” and “Eva.” They were launched alongside the lander on May 5, 2018. Mission controllers weren’t even sure the tiny spacecraft would survive the journey across interplanetary space–but they did. Now they will act as radio relay stations. Instead of waiting several hours for InSight to report back to Earth, WALL-E and Eva will relay entry, descent and landing data much sooner. This is the first time cubesats have traveled beyond Earth orbit, so it will be a significant achievement if they succeed.

NASA will broadcast the landing on NASA TV starting at 2 p.m. EST on Monday, Nov. 26th. Tune in here.

Realtime Space Weather Photo Gallery

Quiet Sun Makes “Musical Waves” in Earth’s Magnetic Field

Nov. 23, 2018: When a stream of solar wind hits Earth, magnetometers around the Arctic Circle normally go haywire, their needles swinging chaotically as local magnetic fields react to the buffeting of the solar wind. On Nov. 18th, however, something quite different happened. Solar wind hit Earth and produced … a pure, almost-musical sine wave:

Rob Stammes recorded the event from the Polarlightcenter, a magnetic observatory in the Lofoten Islands of Norway. “A very stable ~15 second magnetic oscillation commenced and persisted for several hours,” he says. “The magnetic field was swinging back and forth by 0.06 degrees, peak to peak, with the regularity of a metronome.”

Imagine blowing across a piece of paper, making it flutter with your breath. The solar wind can have a similar effect on magnetic fields. The waves Stammes recorded are essentially flutters propagating down the flanks of Earth’s magnetosphere excited by the breath of the sun. Researchers call them “pulsations continuous” — or “Pc” for short.

“A very sensitive magnetometer is required to record these delicate waves,” says Stammes. “I use a mechanical magnetometer with bar magnets suspended from a special wire. LEDs and light detectors in an isolated dark box record the motion of the magnets, while vanes in oil damp out non-magnetic interference.”

Pc waves are classified into 5 types depending on their period. The waves Stammes recorded fall into the range 15 to 45 seconds–that is, Pc3. Researchers have found that Pc3 waves sometimes flow around Earth’s magnetic field and cause a “tearing instability” in our planet’s magnetic tail. This, in turn, can set the stage for an explosion as magnetic fields in the tail reconnect.

A quartet of NASA spacecraft recently flew through just such an explosion. Last week, researchers from the University of New Hampshire reported that four Magnetospheric Multiscale (MMS) spacecraft spent several seconds inside a magnetic reconnection event as they were orbiting through Earth’s magnetic tail. Sensors on the spacecraft recorded jets of high energy particles emerging from the blast site. One jet was aimed squarely at Earth and probably sparked auroras when it hit the upper atmosphere.

Stammes has recorded many Pc waves in the past, “but this is the first time I have detected category Pc3,” he says. “This was a very rare episode indeed.”

Realtime Space Weather Photo Gallery

A Sunspot from the Next Solar Cycle

Nov. 19, 2018: Over the weekend, a small sunspot materialized in the sun’s northern hemisphere, then, hours later, vanished again. Such an occurrence is hardly unusual during solar minimum when sunspots are naturally small and short-lived. However, this ephemeral spot was noteworthy because its magnetic field was reversed–marking it as a member of the next solar cycle.

Shown above is a magnetic map of the sun from NASA’s Solar Dynamics Observatory on Nov. 17th. Two sunspot groups visible at 21:00 UT are inset.

Note sunspot AR2727 just north of the sun’s equator. It is a member of decaying Solar Cycle 24, the cycle that peaked back in 2012-2014. Next, compare its magnetic polarity to that of the other, unnumbered sunspot high above it. They are opposite. According to Hale’s Law, this means the two sunspots belong to different solar cycles. The high latitude sunspot appears to be a harbinger of Solar Cycle 25.

Solar cycles always mix together at their boundaries. Indeed, ephemeral sunspots possibly belonging to Solar Cycle 25 have already been reported on Dec. 20, 2016, and April 8, 2018. Now we can add Nov. 17, 2018, to list. The slow transition between Solar Cycle 24 and Solar Cycle 25 appears to be underway.

What does this mean? First, it suggests that the solar cycle is still operative. This contradicts widespread internet buzz that a Grand Minimum is in the offing, with no new sunspots expected for decades as the solar cycle grinds to a halt. Second, if patterns of previous solar cycles hold, Solar Minimum is not finished. It will probably continue to deepen in the year or so ahead even as new Solar Cycle 25 sunspots occasionally pop up, promising an ultimate end to the lassitude.

The 2018 Leonid Meteor Shower

Nov. 16, 2018: Earth is entering a stream of debris from comet Tempel-Tuttle, source of the annual Leonid meteor shower. Last night, NASA’s network of all-sky meteor cameras detected five Leonid fireballs over the USA, numbers that will grow as we enter the weekend. Forecasters expect the shower to peak on Nov. 17th and 18th with rates as high as 15 meteors per hour.

The Leonids are famous for storming. As often as a few times each century, Earth hits a dense filament of Comet Tempel-Tuttle’s dusty debris, causing thousands of meteors per hour to stream out of the constellation Leo. Such a display in 1833 kickstarted modern meteor astronomy with an outburst of 100,000 Leonids per hour. Many readers still remember the Leonid fireballs of 1998 and the meteor storms of 1999, 2001 and 2002.

2018 is not a storm year, however. Earth will thread the needle between dense filaments, scooping up a lesser amount of dust. Each speck will hit Earth’s upper atmosphere at ~72 km/s (160,000 mph) producing a swift meteor emerging from the constellation Leo. The best time time to look is during the hours before dawn on Saturday, Nov. 17th, and Sunday, Nov. 18th, when the Lion is high in the southeastern sky.

If you do set your alarm for dawn, there’s more to see besides Leonids. For one thing, amateur astronomers have just discovered a new comet in the constellation Virgo. Comet Machholz-Fujikawa-Iwamoto (C/2018 V1) is an easy target for backyard telescopes, shining like a green fuzzy star of 8th magnitude. Use these orbital elements to point your optics.

Not far from the comet, Venus is having a close encounter with the brightest star in Virgo, Spica. Alan Dyer photographed the pair rising over the plains of Alberta, Canada, yesterday morning:

“Venus and Spica rose together as morning stars in the dawn twilight on Nov. 15th,” says Dyer. “Light clouds added the natural glows and enlarged Venus, so it really does look ‘big’ here!”

Amateur Astronomers Discover a Bright New Comet

Nov. 12, 2018: There’s a new comet in the morning sky. Discovered just last week by three amateur astronomers–one in Arizona and two in Japan–Comet Machholz-Fujikawa-Iwamoto (C/2018 V1) has quadrupled in brightness over the past few days. “It is now glowing like a fuzzy 8th magnitude star in the constellation Virgo,” reports Michael Jäger of Turmkogel, Austria, who photographed it on Nov. 11th:

“The discovery of a comet by amateur astronomers is a rare event nowadays because robotic Near-Earth-Object search programs usually catch them first,” he says. “My special congratulations to the three discoverers.”

Comet Machholz-Fujikawa-Iwamoto appears to be a first-time visitor to the inner solar system. It is plunging toward the sun on nearly-parabolic orbit that will take it just inside the orbit of Mercury. Closest approach to the sun (0.38 AU) is on Dec. 3-4; closest approach to Earth (0.67 AU) is Nov. 27th.


Click to view the comet’s 3D orbit

Fresh comets like this one are notoriously unpredictable. They can surge in brightness, seeming to promise a spectacular display, when suddenly they fizzle as fragile deposits of ice are exhausted by solar heat. No one knows if Comet Machholz-Fujikawa-Iwamoto will even become a naked eye object. At the moment it is an easy target for backyard telescopes with the promise of … unpredictability. Stay tuned!

Resources: 3D Orbit; Ephemeris; Orbital Elements; Sky Maps.

Realtime Comet Photo Gallery

Space Weather in Wartime: A Sunspot Detonates Naval Mines

Nov. 9, 2018: Rewind almost 50 years. On Aug. 2nd, 1972, giant sunspot MR11976 began to explode. For the next 2 days it unleashed a series of X-class flares, causing deep radio blackouts on Earth and punishing the solar panels and onboard electronics of satellites in Earth orbit. One CME (cloud of plasma) rocketed across the sun-Earth divide in only 14.6 hours–a record that still stands today. Resulting geomagnetic storms sparked auroras so bright, they cast shadows in countries as far south as Britian.


Above: Images of giant sunspot MR11976 from the Paris Observatory. [more]

The 1972 solar storm is legendary at NASA because it occurred in between two Apollo missions: the crew of Apollo 16 had returned to Earth in April and the crew of Apollo 17 was preparing for a moon landing in December. If the timing had only been a little different, astronauts could have been sickened by radiation, requiring an emergency return home for medical attention.

Turns out, it’s legendary in the Navy, too. According to a research paper just accepted for publication in the journal Space Weather, declassified Naval archives reveal an extraordinary explosion in the sea lanes near Vietnam: “On 4 August (1972) TF-77 aircraft reported some two dozen explosions in a minefield near Hon La over a 30-second time span…Ultimately the Navy concluded that the explosions had been caused by the magnetic perturbations of solar storms, the most intense in more than two decades.”


Above: A magnetogram from Manilla reveals unusual disturbances on Aug. 4-5, 1972. [more]

The authors, led by Delores Knipp of the University of Colorado, continue: “Aerial inspections revealed additional evidence of detonations elsewhere along the coast. The wartime memoirs of a US Navy Mineman-Sailor, Chief Petty Officer Michael Gonzales,state: ‘During the first few weeks of August, a series of extremely strong solar flares caused a fluctuation of the magnetic fields, in and around, South East Asia. The resulting chain of events caused the premature detonation of over 4,000 magnetically sensitive [mines].'”

This prompted the Navy to fast-track the replacement of magnetic-influence-only mines with mines that also required seismic or acoustic triggers during periods of high solar activity.

The August 1972 storms affected Earth in ways that are are only now being fully understood almost 50 years later. Moreover, Knipp and colleagues say the storms could be a previously-unrecognized example of an extreme Carrington-class event, and they urge further scrutiny. Given the experience of the US Navy, who can argue? Read the original research here.

Did an Alien Light Sail just Visit the Solar System?

Nov. 6, 2018: It sounds like a tabloid headline, but in this case it could be real. Mainstream researchers from the Harvard Center for Astrophysics have made the case that interstellar asteroid ‘Oumuamua could in fact be an alien light sail. Their original research was posted Oct. 31st on the moderated preprint server arXiv.org.

The story of ‘Oumuamua begins in October 2017 when it was discovered by Robert Weryk using the Pan-STARRS telescope atop Hawaii’s Haleakalā volcano. Astronomers quickly realized that ‘Oumuamua was something special: The object was hurtling through the Solar System on an unbound “hyperbolic” orbit. It came from the stars. Dramatic changes in the object’s brightness suggested that it was tumbling and asymmetric–thin and wide like a cigar or perhaps a pancake.

oumuamua

This artist’s concept shows how ‘Oumuamua is usually depicted: as a cigar shaped asteroid.

On its way out of the Solar System, something unexpected happened. ‘Oumuamua accelerated as if jets of gas were pushing it forward. Astronomers who initially thought ‘Oumuamua was an asteroid now turned their attention to the comet hypothesis. Comets naturally develop jets after close approaches to the sun, and such jets could explain ‘Oumuamua’s behavior.

Just one problem: “Despite its close Solar approach of only 0.25 AU (inside the orbit of Mercury), ‘Oumuamua shows no sign of any cometary activity, no cometary tail, nor gas emission/absorption lines,” point out the Harvard researchers Shmuel Baily and Abraham Loeb. Moreover, “if outgassing was responsible for the acceleration, then the associated torques would have driven a rapid evolution in ‘Oumuamua’s spin, incompatible with observations.”

So if it’s not an asteroid, and it’s not a comet, what could it be? Loeb, who is the chair of the astronomy department at Harvard University and also chairs the advisory board for the Breakthrough Starshot light sail project, realized that the acceleration profile was key. The non-gravitational acceleration of ‘Oumuamua scaled with distance from the sun (r) as r-2 — just like a light sail would behave.

comethypothesis

The comet hypothesis. Credit: NASA/JPL-Caltech

Modeling ‘Oumuamua as a thin object pushed by solar radiation pressure, Baily and Loeb found that it would fit the observations if it were a sheet of material 0.3 mm to 0.9 mm in thickness with a mass surface density of ~0.1 grams per square cm. “Although extremely thin, such an object would survive an interstellar travel over Galactic distances of  about 5 kiloparsecs, withstanding collisions with gas and dust-grains as well as stresses from rotation and tidal forces,” they wrote.

The researchers are now calling for more observations to look for ‘Oumuamua-like visitors to the Solar System. They could be natural objects created by some unknown process in the interstellar medium–or they might be artificial. “A survey for lightsails as technosignatures in the Solar System is warranted, irrespective of whether ‘Oumuamua is one of them,” they conclude.

Although technical, Baily and Loeb’s paper is well written and unusually readable for nonspecialists. Check it out.