It’s long been predicted that a solar eclipse would cause a bow wave in Earth’s ionosphere. The August 2017 eclipse—called the “Great American Eclipse” because it crossed the continental US— gave scientists a chance to test that prediction. Scientists at MIT’s Haystack Observatory used more than 2,000 GNSS (Global Navigation Satellite System) receivers across the continental US to observe this type of bow wave for the first time.
The Great American Eclipse took 90 minutes to cross the US, with totality lasting only a few minutes at any location. As the Moon’s shadow moved across the US at supersonic speeds, it created a rapid temperature drop. After moving on, the temperature rose again. This rapid heating and cooling is what caused the ionospheric bow wave.
The bow wave itself is made up of fluctuations in the electron content of the ionosphere. The GNSS receivers collect very accurate data on the TEC (Total Electron Content) of the ionosphere. This animation shows the bow wave of electron content moving across the US.
The details of this bow wave were published in a paper by Shun-Rong Zhang and colleagues at MIT’s Haystack Observatory, and colleagues at the University of Tromso in Norway. In their paper, they explain it like this: “The eclipse shadow has a supersonic motion which [generates] atmospheric bow waves, similar to a fast-moving river boat, with waves starting in the lower atmosphere and propagating into the ionosphere. Eclipse passage generated clear ionospheric bow waves in electron content disturbances emanating from totality primarily over central/eastern United States. Study of wave characteristics reveals complex interconnections between the sun, moon, and Earth’s neutral atmosphere and ionosphere.”
The ionosphere stretches from about 50 km to 1000 km in altitude during the day. It swells as radiation from the Sun reaches Earth, and subsides at night. Its size is always fluctuating during the day. It’s called the ionosphere because it’s the region where charged particles created by solar radiation reside. The ionosphere is also where auroras occur. But more importantly, it’s where radio waves propagate.
The ionosphere plays an important role in the modern world. It allows radio waves to travel over the horizon, and also affects satellite communications. This image shows some of the complex ways our communications systems interact with the ionosphere.
There’s a lot going on in the ionosphere. There are different types of waves and disturbances besides the bow wave. A better understanding of the ionosphere is important in our modern world, and the August eclipse gave scientists a chance not only to observe the bow wave, but also to study the ionosphere in greater detail.
The GNSS data used to observe the bow wave was key in another study as well. This one was also published in the journal Geophysical Research Letters, and was led by Anthea Coster of the Haystack Observatory. The data from the network of GNSS was used to detect the Total Electron Content (TEC) and the differential TEC. They then analyzed that data for a couple things during the passage of the eclipse: the latitudinal and longitudinal response of the TEC, and the presence of any Travelling Ionospheric Disturbances (TID) to the TEC.
Predictions showed a 35% reduction in TEC, but the team was surprised to find a reduction of up to 60%. They were also surprised to find structures of increased TEC over the Rocky Mountains, though that was never predicted. These structures are probably linked to atmospheric waves created in the lower atmosphere by the Rocky Mountains during the solar eclipse, but their exact nature needs to be investigated.
“… a giant active celestial experiment provided by the sun and moon.” – Phil Erickson, assistant director at Haystack Observatory.
“Since the first days of radio communications more than 100 years ago, eclipses have been known to have large and sometimes unanticipated effects on the ionized part of Earth’s atmosphere and the signals that pass through it,” says Phil Erickson, assistant director at Haystack and lead for the atmospheric and geospace sciences group. “These new results from Haystack-led studies are an excellent example of how much still remains to be learned about our atmosphere and its complex interactions through observing one of nature’s most spectacular sights — a giant active celestial experiment provided by the sun and moon. The power of modern observing methods, including radio remote sensors distributed widely across the United States, was key to revealing these new and fascinating features.”
The Great American Eclipse has come and gone, but the detailed data gathered during that 90 minute “celestial experiment” will be examined by scientists for some time.
Holy moly, that was awesome! Incredible, fantastic, amazing…there just aren’t the words to describe what it is like to experience totality. While I’m trying to come down to Earth and figure out how to explain how wonderful this was, enjoy the beautiful images captured by our readers from across the US and those from across the world who traveled to capture one of nature’s most spectacular events: a total solar eclipse.
The images from those seeing partial eclipses are wonderful, as well, and we’ll keep adding them as they come in (update, we just got some from Europe too). Great job everyone!
Today, the NASA TV Public Channel is live-streaming their coverage of the totality of the 2017 Solar Eclipse as it covers a path reaching across the continental United States – from Oregon to South Carolina. The event, titled “Solar Eclipse: Through the Eyes of NASA“, begins at 1 p.m. EDT (11 am PDT). Be sure to check it out by following the link below:
Also, NASA has promised a plethora of information on this eclipse, which will include “images captured before, during and after the eclipse by 11 spacecraft, at least three NASA aircraft, more than 50 high-altitude balloons, and the astronauts aboard the International Space Station – each offering a unique vantage point for the celestial event.”
If you’re just reading this now, there’s still time! Head on over and see it all unfold!
On Monday, August 21, 2017, there’s going to be a total eclipse of the Sun, visible to path that goes right through the middle of the United States. You should be making plans to see this, and we’re here to help you know where to go and what to do.
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Imagine if you will, that you are a human being living in prehistoric times. You look up at the sky and see the Sun slowly being blocked out, becoming a ominous black sphere that glows around the edges. Could you really be faulted for thinking that this was some sort of supernatural event, or that the end of the world was nigh?
Of course not. Which is why for thousands of years, human beings believed that solar eclipses were just that – a sign of death or a bad omen. But in fact, an eclipse is merely what happens when one stellar object passes in front of another and obscures it. In astronomy, this happens all the time; and between the Sun, the Moon, and the Earth, total eclipses have been witnessed countless times throughout history.
The general term for when one body passes in front of another in a solar system is transit. This term accurately describes how, depending on your vantage point, stellar bodies pass in front of each other on a regular basis, thus causing the reflected light from that body to be temporarily obscured.
However, when we are talking about how the Moon can pass between the Earth and the Sun, and how the Earth can pass between the Sun and the Moon, we use the term eclipse. This is also known as a syzygy, an astronomical term derived from ancient Greek (meaning “yoked together”) that describes a straight-line configuration between three celestial bodies.
Total Solar Eclipse:
When the Moon passes between the Sun and the Earth, and the Moon fully occults (blocks) the Sun, it is known as the solar eclipse. The type of solar eclipse – total or partial – depends on the distance of the Moon from the Earth during the event.
During an eclipse of the Sun, only a thin path on the surface of the Earth is actually able to experience a total eclipse – which is called the path of totality. People on either side of that path see a partial eclipse, where the Sun is only partly obscured by the Moon, relative to those who are standing in the center and witnessing the maximum point of eclipse.
A total solar eclipse occurs when the Earth intersects the Moon’s umbra – i.e. the innermost and darkest part of its shadow. These are relatively brief events, generally lasting only a few minutes, and can only be viewed along a relatively narrow track (up to 250 km wide). The region where a partial eclipse can be observed is much larger.
During a solar eclipse, the Moon can sometimes perfectly cover the Sun because its size is nearly the same as the Sun’s when viewed from the Earth. This, of course, is an illusion brought on by the fact that the Moon is much closer to us than the Sun.
And since it is closer, it can block the light from the Sun and cast a shadow on the surface of the Earth. If you’re standing within that shadow, the Sun and the Moon appear to line up perfectly, so that the Moon is completely darkened.
After a solar eclipse reaches totality, the Moon will continue to move past the Sun, obscuring smaller and smaller portions of it and allowing more and more light to pass.
Total Lunar Eclipse:
A total eclipse of the Moon is a different story. In this situation, the entire Moon passes into the Earth’s shadow, darkening it fully. A partial lunar eclipse occurs when the shadow of the Earth doesn’t fully cover the Moon, so only part of the Moon is darkened.
Unlike a solar eclipse, a lunar eclipse can be observed from nearly anywhere in an entire hemisphere. In other words, observers all across planet Earth can see this darkening and it appears the same to all. For this reason, total lunar eclipses are much more common and easier to observe from a given location. A lunar eclipse also lasts longer, taking several hours to complete, with totality itself usually averaging anywhere from about 30 minutes to over an hour.
There are three types of lunar eclipses. There’s a penumbral eclipse, when the Moon crosses only the Earth’s penumbra (the region in which only a portion of light is obscured); followed by a partial, when the Moon crosses partially into the Earth’s umbra (where the light is completely blocked).
Last, there is a total eclipse, when the Moon crosses entirely into the Earth’s umbra. A total lunar eclipse involves the Moon passing through all three phases, then gradually passing out of the Earth’s shadow and becoming bright again. Even during a total lunar eclipse, however, the Moon is not completely dark.
Sunlight is still refracted through the Earth’s atmosphere and enters the umbra to provide faint illumination. Similar to what happens during a sunset, the atmosphere scatters shorter wavelength light, causing it to take on a red hue. This is where the phrase ‘Blood Moon‘ comes from.
Since the Moon orbits the Earth, you would expect to see an eclipse of the Sun and the Moon once a lunar month. However, this does not happen simply because the Moon’s orbit isn’t lined up with the Sun. In fact, the Moon’s orbit is tilted by a few degrees – 1.543º between the angle of the ecliptic and the lunar equator, to be exact.
This means that three objects only have the opportunity to line up and cause an eclipse a few times a year. It’s possible for a total of 7 solar and lunar eclipses every year, but that only happens a few times every century.
Other Types of Eclipses:
The term eclipse is most often used to describe a conjunction between the Earth, Sun and Moon. However, it can also refer to such events beyond the Earth–Moon system. For example, a planet moving into the shadow of one of its moons, a moon passing into the shadow of its host planet, or a moon passing into the shadow of another moon.
For instance, during the Apollo 12 mission in 1969, the crew was able to observe the Sun being eclipsed by the Earth. In 2006, during its mission to study Saturn, the Cassini spacecraft was able to capture the image above, which shows the gas giant transiting between the probe and the Sun.
In July of 2015, when the New Horizons mission passed through the shadow of Pluto, it was able to capture a stunning image of the dwarf planet eclipsing the Sun. The image was taken at a distance of about 2 million km (1.25 million miles), which provided the necessary vantage point to see the disc of the Sun become fully obscured.
On top of that, many other bodies in the Solar System can experience eclipses as well. These include the four gas giants, all of which have major moons that periodically transit between the planet and either Earth-based or space-based observatories.
The most impressive and common of these involve Jupiter and its four largest moons (Io, Europa, Ganymede and Callisto). Given the size and low axial tilt of these moons, they often experience eclipses with Jupiter as a result of transits, relative to our instruments.
A well-known example occurred in April of 2014, when the Hubble Space Telescope caught an image of Ganymede passing in front at of Jupiter. At the time the image was taken, Ganymede was casting its shadow within Jupiter’s Great Red Spot, which lent the planet a cyclops-like appearance (see below).
The other three gas giants are known to experiences eclipses as well. However, these only occur at certain periods the planet’s orbit of the Sun, due to their higher inclination between the orbits of their moons and the orbital plane of the planets. For instance, Saturn’s largest moon Titan has been known to only occult the ringed gas giant once about every 15 years.
Pluto has also been known to experience eclipses with is largest moon (and co-orbiting body) Charon. However, in all of these cases, the eclipses are never total, as they do not have the size to obscure the much larger gas giant. Instead, the passage of the moons in front of the larger celestial bodies either cast small shadows on the cloud tops of the gas giants, or lead to an annular eclipse at most.
Similarly, on Mars, only partial solar eclipses are ever possible. This is because Phobos or Deimos are not large enough (or distant enough in their orbits) to cover the Sun’s disc, as seen from the surface of the planet. Phobos and Deimos have also been known to experience lunar eclipses as they slip into the shadow of Mars.
Martian eclipses have been photographed numerous times from both the surface and from orbit. For example, in 2010, the Spirit rover captured images of a Martian lunar eclipse as Phobos, the larger of the two martian moons, was photographed while slipping into the shadow of Mars.
Also, between Nov. 4 and Nov. 5, 2010, the Opportunity rover captured several images (later turned into movies) of a Martian sunset. In the course of imaging the Sun for a total of 17 minutes, Opportunity captured stills of the Sun experiencing a solar eclipse. And on September 13th, 2012 – during the 37th day of its mission (Sol 27) – the Curiosity rover captured an image of Phobos transiting the Sun.
As far as astronomical events go, total eclipses (Lunar and Solar) are not uncommon occurrences. If you ever want to witness a one, all you need to do is keep track of when one will be visible from your part of the world. Some good resources for this are NASA’s Eclipse Website and timeanddate.com.
Or, if you’re the really adventurous type, you can find out where on Earth the next path of totality is going to be, and then book a vacation to go there. Get to the right spot at the right time, and you should be getting the view of a lifetime!
We have written many articles about the eclipse for Universe Today. Here’s a list of articles about specific times when a total Lunar Eclipse took place, and here’s a list of Solar Eclipse articles. And be sure to check out this article and video of an Annular Eclipse.
If the Sun, Earth and Moon are lined up, shouldn’t we get a lunar and solar eclipse every month? Clearly, we don’t, but why not?
Coincidences happen all the time. Right, Universe? One of the most amazing is that Moon and the Sun appear to be almost exactly the same size in the sky and they’re both the size of your pinky fingernail held at arm’s length. These coincidences just keep piling up. Thanks Universe?
There are two kinds of eclipses: solar and lunar. Well, there’s a third kind, but we’d best not think about that.
A solar eclipse occurs when the Moon passes in between the Earth and Sun, casting a shadow down on the surface of our planet. If you’re in the path of the shadow, the Moon destroys the Sun. No, wait, I mean the Moon blocks the Sun briefly.
A lunar eclipse happens when the Moon passes through the Earth’s shadow. We see one limb of the Moon darken until the entire thing is in shadow.
You’ve got the Sun, Earth and Moon all in a line. Where they’re like this, it’s a solar eclipse, and when they’re like this, it’s a lunar eclipse.
If the Moon takes about a month to orbit the Earth, shouldn’t we get an eclipse every two weeks? First a solar eclipse, and then two weeks later, lunar eclipse, back and forth? And occasionally a total one of the heart? But we don’t get them every month, in fact, it can take months and months between eclipses of any kind.
If the Sun, Earth and Moon were truly lined up perfect, this would be the case. But the reality is that they’re not lined up. The Moon is actually on an inclined plane to the Earth.
Imagine the Solar System is a flat disk, like a DVD. You kids still know what those are, right? This is the plane of the ecliptic, and all of the planets are arranged in that disk.
But the Moon is on another disk, which is inclined at an angle of 5.14 degrees. So, if you follow the orbit of the Moon as it goes around the Earth, sometimes it’s above the plane of the ecliptic and sometimes it’s below. So the shadow cast by the Moon misses the Earth, or the shadow cast by the Earth misses the Moon.
But other times, the Sun, Moon and Earth are aligned, and we get eclipses. In fact, eclipses tend to come in pairs, with a solar eclipse followed by a lunar eclipse, because everything is nicely aligned.
Wondering why the Moon turns red during a lunar eclipse? It’s the same reason we see red sunsets here on Earth – the atmosphere filters out the green to violet range of the spectrum, letting the red light pass through.
The Earth’s atmosphere refracts the sunlight so that it’s bent slightly, and can illuminate the Moon during the greatest eclipse. It’s an eerie sight, and well worth hanging around outside to watch it happen. We just had recently had a total lunar eclipse, did you get a chance to see it? Wasn’t it awesome?
Don’t forget about the total solar eclipse that’s going to be happening in August, 2017. It’s going to cross the United States from Oregon to Tennessee and should be perfect viewing for millions of people in North America. We’ve already got our road trip planned out.
Are you planning to see the 2017 eclipse? Tell us your plans in the comments below.
First, the bad news. This weekend’s partial solar eclipse only touches down across the very southern tip of the African continent, Madagascar, a few remote stations in Antarctica, and a few wind-swept islands in the southern Indian Ocean. More than likely, the only views afforded humanity by Sunday’s partial solar eclipse will come out of South Africa, where the eclipse will be about 40% partial around 5:30 Universal Time (UT).
It’s the curious circumstances surrounding the September 13th eclipse that conspire to hide it from the majority of humanity. First, the Moon reaches its ascending node along the plane of the ecliptic at 4:38 UT on Monday, September 14th, nearly 22 hours after New phase. The umbra, or dark inner core of the shadow of Earth’s Moon ‘misses’ the Earth, passing about 380 kilometres or 230 miles above the South Pole. The outer penumbra of the Moon’s shadow just brushes the planet Earth, assuring a 79% maximum obscuration of the Sun over Antarctica around 6:55 UT.
Second, the Moon also reaches its most distant apogee for 2015 on September 14th at 11:29 UT, 406,465 kilometers from the Earth. This is just over 28 hours after New, assuring that the umbra of the Moon falls 25,000 kilometres short of striking the Earth. The eclipse would be an annular one, even if we were in line to see it.
Observers will see the eclipse begin at sunrise over South Africa and the Kalahari Desert, great for photography and catching the eclipse along with foreground objects. Observers will need to follow solar observing safety protocols during all stages of the eclipse. A high value neutral density filter will bring out the silhouette of foreground objects while preserving the image of the partially eclipsed Sun, but remember that such a filter is for photographic use only.
P1, or the first contact of the Moon’s penumbra with the Earth occurs on the morning of the 13th over the Angola/South Africa border at 4:41 UT, and the shadow footprint races across the southern Indian Ocean to depart Earth near the Antarctic coast (P4) at 09:06 UT.
New Moon occurs on September 13th at 6:43 UT, marking the start of lunation 1147.
For saros buffs, this eclipse is a part of saros series 125 (member 54 of 73). Saros 125 started on February 4th, 1060 and produced just four total eclipses in the late 13th and early 14th centuries. Mark your calendars, as this saros will end with a brief partial eclipse on April 8th, 2358. The final total eclipse for this particular saros crossed over central Europe on July 16th, 1330, when an observation by monks near Prague noted “the Sun was so greatly obscured that of its great body, only a small extremity like a three night old Moon was seen.”
Missing out on the eclipse? The good folks over at Slooh have got you covered, with a live webcast set to start at 4:30 UT/12:30 AM EDT.
Planning an ad-hoc webcast of your own from the eclipse viewing zone? Let us know!
There are also some chances to nab the eclipse from space via solar observing satellites in low Earth orbit:
The European Space Agency’s Proba-2 will see eclipses on the following passes – 5:01 UT (partial)/6:31 UT (annular) 8:00 UT (partial).
And JAXA’s Hinode mission will see the same at the following times: 5:56 UT (Partial)/7:46 UT (partial). Unfortunately, there are no good circumstances for an ISS transit this time around, as the ISS never passes far enough south in its orbit.
Looking for more? You can always participate in the exciting pastime of slender moonspotting within 24 hours post or prior to the New Moon worldwide. This feat of extreme visual athletics favors the morning of Saturday, September 12th to sight the slim waning crescent Moon the morning before the eclipse, or the evenings of September 13th and 14th, to spy the waxing crescent Moon on the evenings after.
And this eclipse sets us up for the grand finale: the last total lunar eclipse of the ongoing tetrad on September 28th, visible from North America and Europe. And yes, the Moon will be near perigee to boot… expect Super/Blood Moon wackiness to ensue.
Watch for our complete guide to the upcoming lunar eclipse, with observational tips, factoids, eclipse lunacy and more!
What does a solar eclipse look like from a fast-flying Falcon 7X jet at 14,000 meters (48,000 feet)? French journalist Guillaume Cannat described the Sun as looking black and “ruffled.”
Cannat was part of a group accompanying professional and amateur astronomers on board three Dassault Falcon 7X executive jets that flew in the narrow zone where totality of the eclipse could be observed, from southern Greenland to the geographic North Pole. Traveling through the stratosphere provided the unique opportunity to watch the total eclipse without atmospheric turbulence — which improved the view and the ride. And flying at speeds near Mach .9 also “lengthened” the view of the eclipse to over a minute.
Cannat described the view of totality:
“The crown was deployed around the black disc of the New Moon . It looks like a disheveled silver hair and matted by the solar wind. Far to the left, the planet Venus throws diamond chips, but the absorption of the window hides other celestial body that must always shine in the night daylight. Twilight slides around, bathing the distant clouds in a soft orange glow.”
Here’s a composite of several images of the eclipse that Cannat put together:
The flight was organized by French amateur astronomer Xavier Jubier who created the software Solar Eclipse Maestro. The jets were filled with observation equipment:
Cannat also filmed the eclipse in real time with a GoPro Hero 4. “The whole sequence is rendered in real time so you can relive all in live conditions,” Cannat said. “Note, left, the presence of the bright spot of the planet Venus. The visible light rays around the sun before and after the totality phase are reflections on the window; there are also occasional reflections from inside the cabin. I left her to fully convey the mood of the scene. Naturally, I urge you to watch this video in HD 1080p to capture more detail and better see the spectacular growth of the shadow on cloud strata.”
And here’s a video of the adventure from Dassault Falcon:
Read Cannat’s full account (in French) and see more images at two posts at Le Monde here and here. Our thanks to Guillaume Cannat for sharing his images with Universe Today.
At the turn of the 20th Century, Einstein’s theory of relativity stunned the physics world, but the experimental evidence needed to be found. And so, in 1919, another respected astronomer, Arthur Eddington, observed the deflection of stars by the gravity of the Sun during a solar eclipse. Here’s the story of that famous experiment. Continue reading “Astronomy Cast Ep. 371: The Eddington Eclipse Experiment”
Shining like a beacon in Earth’s sky is the Moon. We’ve seen so much of it in our lifetimes that it’s easy to take it for granted; even the human landings on the Moon in the 1960s and 1970s were eventually taken for granted by the public.
Fortunately for science, we haven’t stopped looking at the Moon in the decades after Neil Armstrong took his first step. Here are a few things to consider about Earth’s closest big neighbor.