To the naked eye, the Sun puts out energy in a continual, steady state, unchanged through human history. (Don’t look at the sun with your naked eye!) But telescopes tuned to different parts of the electromagnetic spectrum reveal the Sun’s true nature: A shifting, dynamic ball of plasma with a turbulent life. And that dynamic, magnetic turbulence creates space weather.
Space weather is mostly invisible to us, but the part we can see is one of nature’s most stunning displays, the auroras. The aurora’s are triggered when energetic material from the Sun slams into the Earth’s magnetic field. The result is the shimmering, shifting bands of color seen at northern and southern latitudes, also known as the northern and southern lights.
There are two things that can cause auroras, but both start with the Sun. The first involves solar flares. Highly-active regions on the Sun’s surface produce more solar flares, which are sudden, localized increase in the Sun’s brightness. Often, but not always, a solar flare is coupled with a coronal mass ejection (CME).
A coronal mass ejection is a discharge of matter and electromagnetic radiation into space. This magnetized plasma is mostly protons and electrons. The CME ejection often just disperses into space, but not always. If it’s aimed in the direction of the Earth, chances are we get increased auroral activity.
The second cause of auroras are coronal holes on the Sun’s surface. A coronal hole is a region on the surface of the Sun that is cooler and less dense than surrounding areas. Coronal holes are the source of fast-moving streams of material from the Sun.
Whether it’s from an active region on the Sun full of solar flares, or whether it’s from a coronal hole, the result is the same. When the discharge from the Sun strikes the charged particles in our own magnetosphere with enough force, both can be forced into our upper atmosphere. As they reach the atmosphere, they give up their energy. This causes constituents in our atmosphere to emit light. Anyone who has witnessed an aurora knows just how striking that light can be. The shifting and shimmering patterns of light are mesmerizing.
The auroras occur in a region called the auroral oval, which is biased towards the night side of the Earth. This oval is expanded by stronger solar emissions. So when we watch the surface of the Sun for increased activity, we can often predict brighter auroras which will be more visible in southern latitudes, due to the expansion of the auroral oval.
Something happening on the surface of the Sun in the last couple days could signal increased auroras on Earth, tonight and tomorrow (March 28th, 29th). A feature called a trans-equatorial coronal hole is facing Earth, which could mean that a strong solar wind is about to hit us. If it does, look north or south at night, depending on where your live, to see the auroras.
Of course, auroras are only one aspect of space weather. They’re like rainbows, because they’re very pretty, and they’re harmless. But space weather can be much more powerful, and can produce much greater effects than mere auroras. That’s why there’s a growing effort to be able to predict space weather by watching the Sun.
A powerful enough solar storm can produce a CME strong enough to damage things like power systems, navigation systems, communications systems, and satellites. The Carrington Event in 1859 was one such event. It produced one of the largest solar storms on record.
That storm occurred on September 1st and 2nd, 1859. It was preceded by an increase in sun spots, and the flare that accompanied the CME was observed by astronomers. The auroras caused by this storm were seen as far south as the Caribbean.
The same storm today, in our modern technological world, would wreak havoc. In 2012, we almost found out exactly how damaging a storm of that magnitude could be. A pair of CMEs as powerful as the Carrington Event came barreling towards Earth, but narrowly missed us.
We’ve learned a lot about the Sun and solar storms since 1859. We now know that the Sun’s activity is cyclical. Every 11 years, the Sun goes through its cycle, from solar maximum to solar minimum. The maximum and minimum correspond to periods of maximum sunspot activity and minimum sunspot activity. The 11 year cycle goes from minimum to minimum. When the Sun’s activity is at its minimum in the cycle, most CMEs come from coronal holes.
NASA’s Solar Dynamics Observatory (SDO), and the combined ESA/NASA Solar and Heliospheric Observatory (SOHO) are space observatories tasked with studying the Sun. The SDO focuses on the Sun and its magnetic field, and how changes influence life on Earth and our technological systems. SOHO studies the structure and behavior of the solar interior, and also how the solar wind is produced.
Several different websites allow anyone to check in on the behavior of the Sun, and to see what space weather might be coming our way. The NOAA’s Space Weather Prediction Center has an array of data and visualizations to help understand what’s going on with the Sun. Scroll down to the Aurora forecast to watch a visualization of expected auroral activity.
NASA’s Space Weather site contains all kinds of news about NASA missions and discoveries around space weather. SpaceWeatherLive.com is a volunteer run site that provides real-time info on space weather. You can even sign up to receive alerts for upcoming auroras and other solar activity.
How would you like to take an all-expenses-paid trip to the Sun? NASA is inviting people around the world to submit their names to be placed on a microchip aboard the Parker Solar Probe mission that will launch this summer. As the spacecraft dips into the blazing hot solar corona your name will go along for the ride. To sign up, submit your name and e-mail. After a confirming e-mail, your digital “seat” will be booked. You can even print off a spiffy ticket. Submissions will be accepted until April 27, so come on down!
The Parker Solar Probe is the size of a small car and named for Prof. Eugene Parker, a 90-year-old American astrophysicist who in 1958 discovered the solar wind. It’s the first time that NASA has named a spacecraft after a living person. The Parker probe will launch between July 31 and August 19 but not immediately head for the Sun. Instead it will make a beeline for Venus for the first of seven flybys. Each gravity assist will slow the craft down and reshape its orbit (see below), so it later can pass extremely close to the Sun. The first flyby is slated for late September.
When heading to faraway places, NASA typically will fly by a planet to increase the spacecraft’s speed by robbing energy from its orbital motion. But a probe can also approach a planet on a different trajectory to slow itself down or reconfigure its orbit.
The spacecraft will swing well within the orbit of Mercury and more than seven times closer than any spacecraft has come to the Sun before. When closest at just 3.9 million miles (6.3 million km), it will pass through the Sun’s outer atmosphere called the corona and be subjected to temperatures around 2,500°F (1,377°C). The primary science goals for the mission are to trace how energy and heat move through the solar corona and to explore what accelerates the solar wind as well as solar energetic particles.
The vagaries of the solar wind, a steady flow of particles that “blows” from the Sun’s corona at more than million miles an hour, can touch Earth in beautiful ways as when it energizes the aurora borealis. But it can also damage spacecraft electronics and poorly protected power grids on the ground. That’s why scientists want to know more about how the corona works, in particular why it’s so much hotter than the surface of the Sun — temperatures there are several million degrees.
As you can imagine, it gets really, really hot near the Sun, so you’ve got to take special precautions. To perform its mission, the spacecraft and instruments will be protected from the Sun’s heat by a 4.5-inch-thick carbon-composite shield, which will keep the four instrument suites designed to study magnetic fields, plasma and energetic particles, and take pictures of the solar wind, all at room temperature.
Similar to how the Juno probe makes close passes over Jupiter’s radiation-fraught polar regions and then loops back out to safer ground, the Parker probe will make 24 orbits around the Sun, spending a relatively short amount of face to face time with our star. At closest approach, the spacecraft will be tearing along at about 430,000 mph, fast enough to get from Washington, D.C., to Tokyo in under a minute, and will temporarily become the fastest manmade object. The current speed record is held by Helios-B when it swung around the Sun at 156,600 mph (70 km/sec) on April 17, 1976.
Many of you saw last August’s total solar eclipse and marveled at the beauty of the corona, that luminous spider web of light around Moon’s blackened disk. When closest to the Sun at perihelion the Parker probe will fly to within 9 solar radii (4.5 solar diameters) of its surface. That’s just about where the edge of the furthest visual extent of the corona merged with the blue sky that fine day, and that’s where Parker will be!
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.
In today’s modern, fast-paced world, human activity is very much reliant on electrical infrastructure. If the power grids go down, our climate control systems will shut off, our computers will die, and all electronic forms of commerce and communication will cease. But in addition to that, human activity in the 21st century is also becoming increasingly dependent upon the infrastructure located in Low Earth Orbit (LEO).
Aside from the many telecommunications satellites that are currently in space, there’s also the International Space Station and a fleet of GPS satellites. It is for this reason that solar flare activity is considered a serious hazard, and mitigation of it a priority. Looking to address that, a team of scientists from Harvard University recently released a study that proposes a bold solution – placing a giant magnetic shield in orbit.
The study – which was the work of Doctor Manasavi Lingam and Professor Abraham Loeb from the Harvard Smithsonian Center for Astrophysicist (CfA) – recently appeared online under the title “Impact and Mitigation Strategy for Future Solar Flares“. As they explain, solar flares pose a particularly grave risk in today’s world, and will become an even greater threat due to humanity’s growing presence in LEO.
Solar flares have been a going concern for over 150 years, ever since the famous Carrington Event of 1859. Since that time, a great deal of effort has been dedicated to the study of solar flares from both a theoretical and observational standpoint. And thanks to the advances that have been made in the past 200 years in terms of astronomy and space exploration, much has been learned about the phenomena known as “space weather”.
At the same time, humanity’s increased reliance on electricity and space-based infrastructure have also made us more vulnerable to extreme space weather events. In fact, if the Carrington event were to take place today, it is estimated that it would cause global damage to electric power grids, satellites communications, and global supply chains.
The cumulative worldwide economic losses, according to a 2009 report by the Space Studies Board (“Severe Space Weather Events–Understanding Societal and Economic Impacts”), would be $10 trillion, and recovery would take several years. And yet, as Professor Loeb explained to Universe Today via email, this threat from space has received far less attention than other possible threats.
“In terms of risk from the sky, most of the attention in the past was dedicated to asteroids,” said Loeb. “They killed the dinosaurs and their physical impact in the past was the same as it will be in the future, unless their orbits are deflected. However, solar flares have little biological impact and their main impact is on technology. But a century ago, there was not much technological infrastructure around, and technology is growing exponentially. Therefore, the damage is highly asymmetric between the past and future.”
To address this, Lingham and Loeb developed a simple mathematical model to assess the economic losses caused by solar flare activity over time. This model considered the increasing risk of damage to technological infrastructure based on two factors. For one, they considered the fact that the energy of a solar flares increases with time, then coupled this with the exponential growth of technology and GDP.
What they determined was that on longer time scales, the rare types of solar flares that are very powerful become much more likely. Coupled with humanity’s growing presence and dependence on spacecraft and satellites in LEO, this will add up to a dangerous conjunction somewhere down the road. Or as Loeb explained:
“We predict that within ~150 years, there will be an event that causes damage comparable to the current US GDP of ~20 trillion dollars, and the damage will increase exponentially at later times until technological development will saturate. Such a forecast was never attempted before. We also suggest a novel idea for how to reduce the damage from energetic particles by a magnetic shield. This was my idea and was not proposed before.”
To address this growing risk, Lingham and Loeb also considered the possibility of placing a magnetic shield between Earth and the Sun. This shield would be placed at the Earth-Sun Lagrange Point 1, where it would be able to deflect charged particles and create an artificial bowshock around Earth. In this sense, this shield would protect Earth’s in a way that is similar to what its magnetic field already does, but to greater effect.
Based on their assessment, Lingham and Loeb indicate that such a shield is technically feasible in terms of its basic physical parameters. They were also able to provide a rudimentary timeline for the construction of this shield, not to mention some rough cost assessments. As Loeb indicated, such a shield could be built before this century is over, and at a fraction of the cost of what would be incurred from solar flare damage.
“The engineering project associated with the magnetic shield that we propose could take a few decades to construct in space,” he said. “The cost for lifting the needed infrastructure to space (weighting 100,000 tons) will likely be of order 100 billions of dollars, much less than the expected damage over a century.”
Interestingly enough, the idea of using a magnetic shield to protect planets has been proposed before. For example, this type of shield was also the subject of a presentation at this year’s “Planetary Science Vision 2050 Workshop“, which was hosted by NASA’s Planetary Science Division (PSD). This shield was recommended as a means of enhancing Mars’ atmosphere and facilitating crewed mission to its surface in the future.
During the course of the presentation, titled “A Future Mars Environment for Science and Exploration“, NASA Director Jim Green discussed how a magnetic shield could protect Mars’ tenuous atmosphere from solar wind. This would allow it to replenish over time, which would have the added benefit of warming Mars up and allowing liquid water to again flow on its surface. If this sounds similar to proposals for terraforming Mars, that’s because it is!
Beyond Earth and the Solar System, the implications for this study are quite overwhelming. In recent years, many terrestrial planets have been found orbiting within nearby M-type (aka. red dwarf) star systems. Because of the way these planets orbit closely to their respective suns, and the variable and unstable nature of M-type stars, scientists have expressed doubts about whether or not these planets could actually be habitable.
In short, scientists have ventured that over the course of billions of years, rocky planets that orbit close to their suns, are tidally-locked with them, and are subject to regular solar flares would lose their atmospheres. In this respect, magnetic shields could be a possible solution to creating extra-solar colonies. Place a large shield in orbit at the L1 Lagrange point, and you never have to worry again about powerful magnetic storms ravaging the planet!
On top of that, this study offers a possible resolution to the Fermi Paradox. When looking for sign of Extra-Terrestrial Intelligence (ETI), it might make sense to monitor distant stars for signs of an orbiting magnetic shield. As Prof. Leob explained, such structures may have already been detected around distant stars, and could explain some of the unusual observations astronomers have made:
“The imprint of a shield built by another civilization could involve the changes it induces in the brightness of the host star due to occultation (similar behavior to Tabby’s star) if the structure is big enough. The situation could be similar to Dyson’s spheres, but instead of harvesting the energy of the star the purpose of the infrastructure is to protect a technological civilization on a planet from the flares of its host star.”
It is a foregone conclusion that as time and technology progress, humanity’s presence in (and reliance on) space will increase. As such, preparing for the most drastic space weather events the Solar System can throw at us just makes sense. And when it comes to the big questions like “are we alone in the Universe?”, it also makes sense to take our boldest concepts and proposals and consider how they might point the way towards extra-terrestrial intelligence.
Earth doesn’t have a corner on auroras. Venus, Mars, Jupiter, Saturn, Uranus and Neptune have their own distinctive versions. Jupiter’s are massive and powerful; Martian auroras patchy and weak.
Auroras are caused by streams of charged particles like electrons that originate with solar winds and in the case of Jupiter, volcanic gases spewed by the moon Io. Whether solar particles or volcanic sulfur, the material gets caught in powerful magnetic fields surrounding a planet and channeled into the upper atmosphere. There, the particles interact with atmospheric gases such as oxygen or nitrogen and spectacular bursts of light result. With Jupiter, Saturn and Uranus excited hydrogen is responsible for the show.
Auroras on Earth, Jupiter and Saturn have been well-studied but not so on the ice-giant planet Uranus. In 2011, the Hubble Space Telescope took the first-ever image of the auroras on Uranus. Then in 2012 and 2014 a team from the Paris Observatory took a second look at the auroras in ultraviolet light using the Space Telescope Imaging Spectrograph (STIS) installed on Hubble.
Two powerful bursts of solar wind traveling from the sun to Uranus stoked the most intense auroras ever observed on the planet in those years. By watching the auroras over time, the team discovered that these powerful shimmering regions rotate with the planet. They also re-discovered Uranus’ long-lost magnetic poles, which were lost shortly after their discovery by Voyager 2 in 1986 due to uncertainties in measurements and the fact that the planet’s surface is practically featureless. Imagine trying to find the north and south poles of a cue ball. Yeah, something like that.
In both photos, the auroras look like glowing dots or patchy spots. Because Uranus’ magnetic field is inclined 59° to its spin axis (remember, this is the planet that rotates on its side!) , the auroral spots appear far from the planet’s north and south geographic poles. They almost look random but of course they’re not. In 2011, the spots lie close to the planet’s north magnetic pole, and in 2012 and 2014, near the south magnetic pole — just like auroras on Earth.
An auroral display can last for hours here on the home planet, but in the case of the 2011 Uranian lights, they pulsed for just minutes before fading away.
Want to know more? Read the team’s findings in detail here.
Coronal Mass Ejections (aka. solar flares) are a seriously hazardous thing. Whenever the Sun emits a burst of these charged particles, it can play havoc with electrical systems, aircraft and satellites here on Earth. Worse yet is the harm it can inflict on astronauts stationed aboard the ISS, who do not have the protection of Earth’s atmosphere. As such, it is obvious why scientists want to be able to predict these events better.
For this reason, the Smithsonian Astrophysical Observatory and the Charles Stark Draper Laboratory – a Cambridge, Massachusetts-based non-profit engineering organization – are working to develop specialized sensors for NASA’s proposed solar spacecraft. Launching in 2018, this spacecraft will fly into the Sun atmosphere and “touch” the face of the Sun to learn more about its behavior.
This spacecraft – known as the Solar Probe Plus (SPP) – is currently being designed and built by the Johns Hopkins University Applied Physics Laboratory. Once it is launched, the SPP will use seven Venus flybys over nearly seven years to gradually shrink its orbit around the Sun. During this time, it will conduct 24 flybys of the Sun and pass into the Sun’s upper atmosphere (corona), passing within 6.4 million km (4 million mi) of its surface.
At this distance, it will have traveled 37.6 million km (23.36 million mi) closer to the Sun than any spacecraft in history. At the same time, it will set a new record for the fastest moving object ever built by human beings – traveling at speeds of up to 200 km/sec (124.27 mi/s). And last but not least, it will be exposed to heat and radiation that no spacecraft has ever faced, which will include temperatures in excess of 1371 °C (2500 °F).
As Seamus Tuohy, the Director of the Space Systems Program Office at Draper, said in a CfA press release:
“Such a mission would require a spacecraft and instrumentation capable of withstanding extremes of radiation, high velocity travel and the harsh solar condition—and that is the kind of program deeply familiar to Draper and the Smithsonian Astrophysical Observatory.”
In addition to being an historic first, this probe will provide new data on solar activity and help scientists develop ways of forecasting major space-weather events – which impact life on Earth. This is especially important in an age when people are increasingly reliant on technology that can be negatively impacted by solar flares – ranging from aircraft and satellites to appliances and electrical devices.
According to a recent study by the National Academy of Sciences, it is estimated that a huge solar event today could cause two trillion dollars in damage in the US alone – and places like the eastern seaboard would be without power for up to a year. Without electricity to provide heating, utilities, light, and air-conditioning, the death toll from such an event would be significant.
As such, developing advanced warning systems that could reliably predict when a coronal mass ejection is coming is not just a matter of preventing damage, but saving lives. As Justin C. Kasper, the principal investigator at the Smithsonian Astrophysical Observatory and a professor in space science at the University of Michigan, said:
“[I]n addition to answering fundamental science questions, the intent is to better understand the risks space weather poses to the modern communication, aviation and energy systems we all rely on. Many of the systems we in the modern world rely on—our telecommunications, GPS, satellites and power grids—could be disrupted for an extended period of time if a large solar storm were to happen today. Solar Probe Plus will help us predict and manage the impact of space weather on society.”
To this end, the SPP has three major scientific objectives. First, it will seek to trace the flow of energy that heats and accelerates the solar corona and solar wind. Second, its investigators will attempt to determine the structure and dynamics of plasma and magnetic fields as the source of solar wind. And last, it will explore the mechanisms that accelerate and transport energetic particles – specifically electrons, protons, and helium ions.
To do this, the SPP will be equipped with an advanced suite of instruments. One of the most important of these is the one built by the Smithsonian Astrophysical Observatory with technical support from Draper. Known as the Faraday Cup – and named after famous electromagnetic scientists Michael Faraday – this device will be operated by SAO and the University of Michigan in Ann Arbor.
Designed to withstand interference from electromagnetic radiation, the Farady Cup will measure the velocity and direction of the Sun’s charged particles, and will be only two positioned outside of the SPP’s protective sun shield – another crucial component. Measuring 11.43 cm (4.5 inches) thick, this carbon composition shield will ensure that the probe can withstand the extreme conditions as it conducts its many flybys through the Sun’s corona.
Naturally, the mission presents several challenges, not the least of which will be capturing data while operating within an extreme environment, and while traveling at extreme speeds. But the payoff is sure to be worth it. For years, astronomers have studied the Sun, but never from inside the Sun’s atmosphere.
By flying through the birthplace of the highest-energy solar particles, the SPP is set to advance our understanding of the Sun and the origin and evolution of the solar wind. This knowledge could not only help us avoid a natural catastrophe here on Earth, but help advance our long-term goal of exploring (and even colonizing) the Solar System.
Not many people get excited about a penumbral eclipse, but when it’s a deep one and the only lunar eclipse visible in North America this year, it’s worth a closer look. What’s more, this Friday’s eclipse happens during convenient, early-evening viewing hours. No getting up in the raw hours before dawn.
During a partial or total lunar eclipse, the full moon passes first through the Earth’s outer shadow, called the penumbra, before entering the dark, interior shadow or umbra. The penumbra is nowhere near as dark as the inner shadow because varying amounts of direct sunlight filter into it, diluting its duskiness.
To better understand this, picture yourself watching the eclipse from the center of the Moon’s disk (latitude 0°, longitude 0°). As you look past the Earth toward the Sun, you would see the Sun gradually covered or eclipsed by the Earth. Less sunlight would be available to illuminate the Moon, so your friends back on Earth would notice a gradual dimming of the Moon, very subtle at first but becoming more noticeable as the eclipse progressed.
As the Moon’s leading edge approached the penumbra-umbra border, the Sun would narrow to a glaring sliver along Earth’s limb for our lucky lunar observer. Back on Earth, we’d notice that the part of the Moon closest to the umbra looked strangely gray and dusky, but the entire lunar disk would still be plainly visible. That’s what we’ll see during Friday’s eclipse. The Moon will slide right up to the umbra and then roll by, never dipping its toes in its dark waters.
During a partial eclipse, the Moon keeps going into the umbra, where the Sun is completely blocked from view save for dash of red light refracted by the Earth’s atmosphere into what would otherwise be an inky black shadow. This eclipse, the Moon only flirts with the umbra.
Because the moon’s orbit is tilted about 5° from the plane of Earth’s orbit, it rarely lines up for a perfect bullseye total eclipse: Sun – Earth – Moon in a straight line in that order. Instead, the moon typically passes a little above or below (north or south) of the small, circle-shaped shadow cast by our planet, and no eclipse occurs. Or it clips the outer edge of the shadow and we see — you guessed it — a penumbral eclipse.
Earth’s shadow varies in size depending where you are in it. Standing on the ground during twilight, it can grow to cover the entire sky, but at the moon’s distance of 239,000 miles, the combined penumbra and umbra span just 2.5° of sky or about the width of your thumb held at arm’s length.
Because the Moon travels right up to the umbra during Friday’s eclipse, it will be well worth watching.The lower left or eastern half of the moon will appear obviously gray and blunted especially around maximum eclipse as it rises in the eastern sky that Friday evening over North and South America. I should mention here that the event is also visible from Europe, Africa, S. America and much of Asia.
For the U.S., the eastern half of the country gets the best views. Here are CSTand UTtimes for the different stages. To convert from CST, add an hour for Eastern, subtract one hour for Mountain and two hours for Pacific times. UT stands for Universal Time, which is essentially the same as Greenwich or “London” Time except when Daylight Saving Time is in effect:
Eclipse begins: 4:34 p.m. (22:34 p.m. UT) Maximum eclipse (moon deepest in shadow): 6:44 p.m. (00:43 UT Feb. 11) Eclipse ends: 8:53 p.m. (2:53 UT Feb. 11)
You can see that the eclipse plays out over more than 4 hours, though I don’t expect most of us will either be able or would want to devote that much time. Instead, give it an hour or so when the Moon is maximally in shadow from 6 to 7:30 p.m. CST; 7-8:30 EST; 5-6:30 p.m. MST and around moonrise Pacific time.
This should be a fine and obvious eclipse because around the time of maximum, the darkest part of the penumbra shades the dark, mare-rich northern hemisphere of the Moon. Dark plus dark equals extra dark! Good luck and clear skies!
Water. It’s always about the water when it comes to sizing up a planet’s potential to support life. Mars may possess some liquid water in the form of occasional salty flows down crater walls, but most appears to be locked up in polar ice or hidden deep underground. Set a cup of the stuff out on a sunny Martian day today and depending on conditions, it could quickly freeze or simply bubble away to vapor in the planet’s ultra-thin atmosphere.
Evidence of abundant liquid water in former flooded plains and sinuous river beds can be found nearly everywhere on Mars. NASA’s Curiosity rover has found mineral deposits that only form in liquid water and pebbles rounded by an ancient stream that once burbled across the floor of Gale Crater. And therein lies the paradox. Water appears to have gushed willy-nilly across the Red Planet 3 to 4 billion years ago, so what’s up today?
Blame Mars’ wimpy atmosphere. Thicker, juicier air and the increase in atmospheric pressure that comes with it would keep the water in that cup stable. A thicker atmosphere would also seal in the heat, helping to keep the planet warm enough for liquid water to pool and flow.
Different ideas have been proposed to explain the putative thinning of the air including the loss of the planet’s magnetic field, which serves as a defense against the solar wind.
Convection currents within its molten nickel-iron core likely generated Mars’ original magnetic defenses. But sometime early in the planet’s history the currents stopped either because the core cooled or was disrupted by asteroid impacts. Without a churning core, the magnetic field withered, allowing the solar wind to strip away the atmosphere, molecule by molecule.
Solar wind eats away the Martian atmosphere
Measurements from NASA’s current MAVEN mission indicate that the solar wind strips away gas at a rate of about 100 grams (equivalent to roughly 1/4 pound) every second. “Like the theft of a few coins from a cash register every day, the loss becomes significant over time,” said Bruce Jakosky, MAVEN principal investigator.
The team first considered the effects of CO2, an obvious choice since it comprises 95% of Mars’ present day atmosphere and famously traps heat. But when you take into account that the Sun shone 30% fainter 4 billion years ago compared to today, CO2 alone couldn’t cut it.
“You can do climate calculations where you add CO2 and build up to hundreds of times the present day atmospheric pressure on Mars, and you still never get to temperatures that are even close to the melting point,” said Robin Wordsworth, assistant professor of environmental science and engineering at SEAS, and first author of the paper.
Carbon dioxide isn’t the only gas capable of preventing heat from escaping into space. Methane or CH4 will do the job, too. Billions of years ago, when the planet was more geologically active, volcanoes could have tapped into deep sources of methane and released bursts of the gas into the Martian atmosphere. Similar to what happens on Saturn’s moon Titan, solar ultraviolet light would snap the molecule in two, liberating hydrogen gas in the process.
When Wordsworth and his team looked at what happens when methane, hydrogen and carbon dioxide collide and then interact with sunlight, they discovered that the combination strongly absorbed heat.
Carl Sagan,American astronomer and astronomy popularizer, first speculated that hydrogen warming could have been important on early Mars back in 1977, but this is the first time scientists have been able to calculate its greenhouse effect accurately. It is also the first time that methane has been shown to be an effective greenhouse gas on early Mars.
When you take methane into consideration, Mars may have had episodes of warmth based on geological activity associated with earthquakes and volcanoes. There have been at least three volcanic epochs during the planet’s history — 3.5 billion years ago (evidenced by lunar mare-like plains), 3 billion years ago (smaller shield volcanoes) and 1 to 2 billion years ago, when giant shield volcanoes such as Olympus Monswere active. So we have three potential methane bursts that could rejigger the atmosphere to allow for a mellower Mars.
The sheer size of Olympus Mons practically shouts massive eruptions over a long period of time. During the in-between times, hydrogen, a lightweight gas, would have continued to escape into space until replenished by the next geological upheaval.
“This research shows that the warming effects of both methane and hydrogen have been underestimated by a significant amount,” said Wordsworth. “We discovered that methane and hydrogen, and their interaction with carbon dioxide, were much better at warming early Mars than had previously been believed.”
I’m tickled that Carl Sagan walked this road 40 years ago. He always held out hope for life on Mars. Several months before he died in 1996, he recorded this:
” … maybe we’re on Mars because of the magnificent science that can be done there — the gates of the wonder world are opening in our time. Maybe we’re on Mars because we have to be, because there’s a deep nomadic impulse built into us by the evolutionary process, we come after all, from hunter gatherers, and for 99.9% of our tenure on Earth we’ve been wanderers. And, the next place to wander to, is Mars. But whatever the reason you’re on Mars is, I’m glad you’re there. And I wish I was with you.”
From here on Earth, the Sun like a smooth ball of light. And prior to Galileo’s discovery of sunposts, astronomers even thought it was a perfect orb with no imperfections. However, thanks to improved instruments and many centuries of study, we know that the Sun is much like the planets of our Solar System.
In addition to imperfections on its surface, the Sun is also made up of several layers, each of which serves its own purpose. It’s this structure of the Sun that powers this massive engine that provides the planets with all the light and heat they receive. And here on Earth, it is what provides all life forms with the energy they need to thrive and survive.
If you could take the Sun apart, and stack up its various elements, you would find that the Sun is made of hydrogen (74%) and helium (about 24%). Astronomers consider anything heavier than helium to be a metal. The remaining amount of the Sun is made of iron, nickel, oxygen, silicon, sulfur, magnesium, carbon, neon, calcium and chromium. In fact, the Sun is 1% oxygen; and everything else comes out of that last 1%.
Where did these elements come from? The hydrogen and helium came from the Big Bang. In the early moments of the Universe, the first element, hydrogen, formed from the soup of elementary particles. The pressure and temperatures were still so intense that the entire Universe had the same conditions as the core of a star.
Hydrogen was fused into helium until the Universe cooled down enough that this reaction couldn’t happen any more. The ratios of hydrogen and helium that we see in the Universe today were created in those first few moments after the Big Bang. The other elements were created in other stars. Stars are constantly fusing hydrogen into helium in their cores.
Once the hydrogen in the core runs out, they switch to fusing heavier and heavier elements, like helium, lithium, oxygen. Most of the heavier metals we see in the Sun were formed in other stars at the end of their lives. The heaviest elements, like gold and uranium, were formed when stars many times more massive that our Sun detonated in supernova explosions.
In a fraction of a second, as a black hole was forming, elements were crushed together in the intense heat and pressure to form the heaviest elements. The explosion scattered these elements across the region, where they could contribute to the formation of new stars.
Our Sun is made up of elements left over from the Big Bang, elements formed from dying stars, and elements created in supernovae. That’s pretty amazing.
Although the Sun is mostly just a ball of hydrogen and helium, it’s actually broken up into distinct layers. The layers of the Sun are created because the temperatures and pressures increase as you move towards the center of the Sun. The hydrogen and helium behave differently under the changing conditions.
The Core: Let’s start at the innermost layer of the Sun, the core of the Sun. This is the very center of the Sun, where temperatures and pressures are so high that fusion can happen. The Sun is combining hydrogen into helium atoms, and this reaction gives off the light and heat that we see here on Earth. The density of the core is 150 times the density of water, and the temperatures are thought to be 13,600,000 degrees Kelvin.
Astronomers believe that the core of the Sun extends from the center out to about 0.2 solar radius. And within this region, temperatures and pressures are so high that hydrogen atoms are torn apart to form separate protons, neutrons and electrons. With all of these free floating particles, the Sun is able to reform them into atoms of helium.
This reaction is exothermic. That means that the reaction gives off a tremendous amount of heat – 3.89 x 1033 ergs of energy every second. The light pressure of all this energy streaming from the core of the Sun is what stops it from collapsing inward on itself.
Radiative Zone: The radiative zone of the Sun starts at the edge of the core of the Sun (0.2 solar radii), and extends up to about 0.7 radii. Within the radiative zone, the solar material is hot and dense enough that thermal radiation transfers the heat of the core outward through the Sun.
The core of the Sun is where nuclear fusion reactions are happening – protons are merged together to create atoms of helium. This reaction produces a tremendous amount of gamma radiation. These photons of energy are emitted, absorbed, and then emitted again by various particles in the radiative zone.
The path that photons take is called the “random walk”. Instead of going in a straight beam of light, they travel in a zigzag direction, eventually reaching the surface of the Sun. In fact, it can take a single photon upwards of 200,000 years to make the journey through the radiative zone of the Sun.
As they transfer from particle to particle, the photons lose energy. That’s a good thing, since we wouldn’t want only gamma radiation streaming from the Sun. Once these photons reach space, they take a mere 8 minutes to get to Earth.
Most stars will have radiative zones, but their size depends on the star’s size. Small stars will have much smaller radiative zones, and the convective zone will take up a larger portion of the star’s interior. The smallest stars might not have a radiative zone at all, with the convective zone reaching all the way down to the core. The largest stars would have the opposite situation, where the radiative zone reaches all the way up to the surface.
Convective Zone: Outside the radiative zone is another layer, called the convective zone, where heat from inside the Sun is carried up by columns of hot gas. Most stars have a convective zone. In the case of the Sun, it starts at around 70% of the Sun’s radius and goes to the outer surface (the photosphere).
Gas deeper inside the star is heated up so that it rises, like globs of wax in a lava lamp. As it gets to the surface, the gas loses some of its heat, cools down, and sinks back towards the center to pick up more heat. Another example would be a pot of boiling water on the stove.
The surface of the Sun looks granulated. These granules are the columns of hot gas that carry heat to the surface. They can be more than 1,000 km across, and typically last about 8 to 20 minutes before dissipating. Astronomers think that low mass stars, like red dwarfs, have a convective zone that goes all the way down to the core. Unlike the Sun, they don’t have a radiative zone at all.
Photosphere: The layer of the Sun that we can see from Earth is called the photosphere. Below the photosphere, the Sun becomes opaque to visible light, and astronomers have to use other methods to probe its interior. The temperature of the photosphere is about 6,000 Kelvin, and gives off the yellow-white light that we see.
Above the photosphere is the atmosphere of the Sun. Perhaps the most dramatic of these is the corona, which is visible during a total solar eclipse.
Below is a diagram of the Sun, originally developed by NASA for educational purposes.
Visible, IR and UV radiation – The light that we see coming from the Sun is visible, but if you close your eyes and just feel the warmth, that’s IR, or infrared radiation. And the light that gives you a sunburn is ultraviolet (UV) radiation. The Sun produces all of these wavelengths at the same time.
Photosphere 6000 K – The photosphere is the surface of the Sun. This is the region where light from the interior finally reaches space. The temperature is 6000 K, which is the same as 5,700 degrees C.
Photosphere 6000 K – The photosphere is the surface of the Sun. This is the region where light from the interior finally reaches space. The temperature is 6000 K, which is the same as 5,700 degrees C.
Radio emissions – In addition to visible, IR and UV, the Sun also gives off radio emissions, which can be detected by a radio telescope. These emissions rise and fall depending on the number of sunspots on the surface of the Sun.
Coronal Hole – These are regions on the Sun where the corona is cooler, darker and has less dense plasma.
2100000 – This is the temperature of the Sun’s radiative zone.
Convective zone/Turbulent convection – This is the region of the Sun where heat from the core is transferred through convection. Warm columns of plasma rise to the surface in columns, release their heat and then fall back down to heat up again.
Coronal loops – These are loops of plasma in the Sun’s atmosphere that follows magnetic flux lines. They look like big arches, stretching up from the surface of the Sun for hundreds of thousands of kilometers.
Core – The is the heart of the Sun, where the temperatures and pressures are so high that nuclear fusion reactions can happen. All of the energy coming from the Sun originates from the core.
14500000 K – The temperature of the core of the Sun.
Radiative Zone – The region of the Sun where energy can only be transferred through radiation. It can take a single photon 200,000 years to get from the core, through the radiative zone, out to the surface and into space.
Neutrinos – Neutrinos are nearly mass-less particles blasted out from the Sun as part of the fusion reactions. There are millions of neutrinos passing through your body every second, but they don’t interact, so you can’t feel them.
Chromospheric Flare – The Sun’s magnetic field can get twisted up and then snap into a different configuration. When this happens, there can be powerful X-ray flares emanating from the surface of the Sun.
Magnetic Field Loop – The Sun’s magnetic field extends out above its surface, and can be seen because hot plasma in the atmosphere follows the field lines.
Spot – A sunspot. These are areas on the Sun’s surface where the magnetic field lines pierce the surface of the Sun, and they’re relatively cooler than the surrounding areas.
Prominence – A bright feature that extends above the surface of the Sun, often in the shape of a loop.
Energetic particles – There can be energetic particles blasting off the surface of the Sun to create the solar wind. In solar storms, energetic protons can be accelerated to nearly the speed of light.
X-rays – In addition to the wavelengths we can see, there are invisible X-rays coming from the Sun, especially during flares. The Earth’s atmosphere protects us from this radiation.
Bright spots and short-lived magnetic regions – The surface of the Sun has many brighter and dimmer spots caused by changing temperature. The temperature changes from the constantly shifting magnetic field.
Yes, the Sun is like an onion. Peel back one layer and you’ll find many more. But in this case, each layers is responsible for a different function. And what they add to is a giant furnace and light source that keeps us living beings here on Earth warm and illuminated!
And be sure to enjoy this video from the NASA Goddard Center, titled “Snapshots from the Edge of the Sun”:
Ever since astronomers first began using telescopes to get a better look at the heavens, they have struggled with a basic conundrum. In addition to magnification, telescopes also need to be able to resolve the small details of an object in order to help us get a better understanding of them. Doing this requires building larger and larger light-collecting mirrors, which requires instruments of greater size, cost and complexity.
However, scientists working at NASA Goddard’s Space Flight Center are working on an inexpensive alternative. Instead of relying on big and impractical large-aperture telescopes, they have proposed a device that could resolve tiny details while being a fraction of the size. It’s known as the photon sieve, and it is being specifically developed to study the Sun’s corona in the ultraviolet.
Basically, the photon sieve is a variation on the Fresnel zone plate, a form of optics that consist of tightly spaced sets of rings that alternate between the transparent and the opaque. Unlike telescopes which focus light through refraction or reflection, these plates cause light to diffract through transparent openings. On the other side, the light overlaps and is then focused onto a specific point – creating an image that can be recorded.
The photon sieve operates on the same basic principles, but with a slightly more sophisticated twist. Instead of thin openings (i.e. Fresnel zones), the sieve consists of a circular silicon lens that is dotted with millions of tiny holes. Although such a device would be potentially useful at all wavelengths, the Goddard team is specifically developing the photon sieve to answer a 50-year-old question about the Sun.
Essentially, they hope to study the Sun’s corona to see what mechanism is heating it. For some time, scientists have known that the corona and other layers of the Sun’s atmosphere (the chromosphere, the transition region, and the heliosphere) are significantly hotter than its surface. Why this is has remained a mystery. But perhaps, not for much longer.
As Doug Rabin, the leader of the Goddard team, said in a NASA press release:
“This is already a success… For more than 50 years, the central unanswered question in solar coronal science has been to understand how energy transported from below is able to heat the corona. Current instruments have spatial resolutions about 100 times larger than the features that must be observed to understand this process.”
With support from Goddard’s Research and Development program, the team has already fabricated three sieves, all of which measure 7.62 cm (3 inches) in diameter. Each device contains a silicon wafer with 16 million holes, the sizes and locations of which were determined using a fabrication technique called photolithography – where light is used to transfer a geometric pattern from a photomask to a surface.
However, in the long-run, they hope to create a sieve that will measure 1 meter (3 feet) in diameter. With an instrument of this size, they believe they will be able to achieve up to 100 times better angular resolution in the ultraviolet than NASA’s high-resolution space telescope – the Solar Dynamics Observatory. This would be just enough to start getting some answers from the Sun’s corona.
In the meantime, the team plans to begin testing to see if the sieve can operate in space, a process which should take less than a year. This will include whether or not it can survive the intense g-forces of a space launch, as well as the extreme environment of space. Other plans include marrying the technology to a series of CubeSats so a two-spacecraft formation-flying mission could be mounted to study the Sun’s corona.
In addition to shedding light on the mysteries of the Sun, a successful photon sieve could revolution optics as we know it. Rather than being forced to send massive and expensive apparatus’ into space (like the Hubble Space Telescope or the James Webb Telescope), astronomers could get all the high-resolution images they need from devices small enough to stick aboard a satellite measuring no more than a few square meters.
This would open up new venues for space research, allowing private companies and research institutions the ability to take detailed photos of distant stars, planets, and other celestial objects. It would also constitute another crucial step towards making space exploration affordable and accessible.