On Monday, Aug. 21, for the first time in almost 100 years, all of North America will be treated to an eclipse of the sun. Those in the path of totality, running from Oregon to South Carolina, will experience one of nature’s most awe-inspiring events — a total solar eclipse.
Scientists, researchers and experts from NASA’s Marshall Space Flight Center in Huntsville, Alabama, will mobilize to experience the eclipse and share it with others. They will join participants from across the agency for a multi-hour broadcast, titled Eclipse Across America: Through the Eyes of NASA, to offer unprecedented live video of the celestial event, along with coverage of activities in parks, libraries, stadiums, festivals and museums across the nation, and on social media.
“It’s going to be a spectacular event,” said Marshall Chief Scientist James Spann. “We’ll be sharing our research and work with people and letting them know how to safely view the eclipse, not only at the events in the path of totality, but also worldwide online and on NASA Television. Excited doesn’t begin to describe how our team feels right now. It truly will be breath-taking, and we can’t wait.”
Marshall experts will be located at two of the broadcast’s 15 locations — Hopkinsville, Kentucky, and Austin Peay State University in Clarksville, Tennessee.
Marshall’s Meteoroid Environment Office’s very own Dr. Bill Cooke, created this graphic showing the idealized view through a telescope with an H-alhpa filter at maximum eclipse for 4 locations: Birmingham, which will experience a 93% eclipse, Atlanta, which will have 97% of the Sun covered, the 97% eclipse in Huntsville, and the 99.6% eclipse in Chattanooga, which shows only the tiniest sliver of Sun down on the bottom.
At NASA, we get very excited about many astronomical events — to name just a few, the return of Halley’s Comet back in 1985/86; the impact of the fragments of Comet Shoemaker-Levy 9 with Jupiter in 1992; the Leonid meteor storms of 1998, 1999, 2001 and 2002; and, of course, the upcoming total solar eclipse on Aug. 21 of this year.
Some of these events get blown a bit out of proportion. A classic example is that every time Mars comes to opposition (closest approach to Earth), the internet reverberates with the very false statement that Mars will appear as large as the Moon at that time. Nothing could be farther from the truth, as Mars, at its very closest to Earth, appears only 1/70th the apparent diameter of the Moon.
This year we have a new one — reports are circulating that this year’s Perseids will be the “brightest shower in recorded human history,” lighting up the night sky and even having some meteors visible during the day. We wish this were true… but no such thing is going to happen.
In this 30 second exposure, a meteor streaks across the sky during the annual Perseid meteor shower Thursday, Aug. 13, 2015, in Spruce Knob, West Virginia. Photo Credit: (NASA/Bill Ingalls)
For one thing, the Perseids never reach storm levels (thousands of meteors per hour). At best, they outburst from a normal rate between 80-100 meteors per hour to a few hundred per hour. The best Perseid performance of which we are aware occurred back in 1993, when the peak Perseid rate topped 300 meteors per hour. Last year also saw an outburst of just over 200 meteors per hour.
This year, we are expecting enhanced rates of about 150 per hour or so, but the increased number will be cancelled out by the bright Moon, the light of which will wash out the fainter Perseids. A meteor every couple of minutes is good, and certainly worth going outside to look, but it is hardly the “brightest shower in human history.” The Leonid meteor storms of the late 1990’s and early 2000’s were much more spectacular, and had rates 10 times greater than the best Perseid display.
So, if not this year’s Perseid shower, what was the greatest meteor show of all time? I think many meteor researchers would give that award to the 1833 Leonids, which had rates of tens of thousands, perhaps even 100,000, meteors per hour. During a good Perseid shower under ideal conditions, you can see about one meteor per minute. Now imagine yourself being back in 1833, on the night of Nov. 12. Looking outside, you would see something like 20 to 30 meteors PER SECOND. No wonder we read accounts like this one from South Carolina (Chambers, A Handbook of Descriptive and Practical Astronomy, Volume 1, 1889):
“Upwards of 100 lay prostrate on the ground…with their hands raised, imploring God to save the world and them. The scene was truly awful; for never did rain fall much thicker than the meteors fell towards the Earth; east, west, north and south, it was the same.”
Now, THAT’s a meteor shower. The 1833 storm had a profound effect on those that witnessed it; it also gave birth to modern meteor science. Those of us who study meteors dream of such a display happening sometime within our lifetimes.
But it won’t be caused by this year’s Perseids.
Cooke leads NASA’s Meteoroid Environment Office at the agency’s Marshall Space Flight Center.
The motion of the moon is what causes eclipses, but the dramatic change in sunlight is what makes them so impressive to observers. But what exactly is happening when the moon passes in front of the sun?
The moon is blocking the sun’s light from reaching Earth, but there is more to the situation than just that. Their relative distance to Earth is one of the most important factors.
The sun is about 400 times farther from Earth than the moon and has a diameter about 400 times larger than the moon. As a result, both the sun and moon (near perigee) appear to be the same size in the sky, allowing the moon to perfectly block out the sun and cast a shadow on Earth during a total eclipse.
The shadow we see while in the path of totality is called the umbra, and the shadow of the surrounding partial eclipse is a penumbra. The shadow from an annular eclipse (when the moon appears smaller than the sun during an eclipse, and so a ring of light is visible around it) is called an anteumbra.
The physics of how each type of shadow is formed is difficult to explain but easy to visualize, so before I tell you about them, here is a picture (technically a ray diagram) of what happens during an eclipse:
Each of the three types of solar eclipse are caused by the moon blocking light from different parts of the sun. Credit: Wikimedia Cmglee
For a total eclipse, the moon has to block out all of the sun’s light. To put the moon in the best position, imagine that a person on Earth is standing under the exact middle of the moon, the centerline of a total solar eclipse.
In this case, light coming from the middle of the sun is clearly going to be blocked by the moon, since it is directly in the way and visible light cannot penetrate rock. The most difficult light to block will be coming from the top and bottom of the sun.
To figure out whether the light will be blocked, a bit of drawing can help. If the light is coming from the exact bottom of the sun and you are wondering if a person can see the light while under the exact center of the moon, draw a line between where the light starts and the person’s eyes.
Does the moon get in the way of the line? If yes, then the person is experiencing a total solar eclipse. None of the sun’s light can get past the moon, so the sun is fully blocked.
If the answer is no, but the person is still standing under the center of the moon, then they are in an annular eclipse. The moon is in the perfect position to block all of the sun’s light, but it still fails to do so. In this case, it will appear to be a large black circle with a ring of sunlight called an annulus around it.
A partial eclipse is the most difficult to explain, since it has the most variability. All but a sliver of the sun may be blocked, or the moon can barely cover any of the sun. In general though, a partial solar eclipse happens when the moon is not quite directly between the observer and sun, but is still in the way of some sunlight.
You can use the same process for determining whether a person is experiencing a total solar eclipse to figure out if they are in the penumbral shadow of the moon. A slight complication is that the moon is off center, so it matters more where the origin point of the light is.
If the person is standing a little north of the moon’s center, then the line from origin to person should start from the sun’s southernmost point, the bottom, since the northern light is less likely to be blocked due to the moon being a bit more to the south from the person’s perspective.
If any of the sun’s light is blocked by the moon, then the person is experiencing a partial solar eclipse. The limit of this blockage, where only the slightest amount of sunlight is blocked, is the edge of the penumbra shadow.
If the moon is not blocking any light, then the moon may be close to the sun but there is no eclipse happening on that spot of Earth.
On Aug. 21, 2017, a total solar eclipse will cross the full continental United States along a narrow, 70-mile-wide path from Oregon to South Carolina.
The last total eclipse in the U.S. was in 1979. And the last total solar eclipse that crossed the entire continental U.S. happened in 1918. But why? Why has it been 99 years, and why have the intervening partial and even total eclipses caught only parts of the country?
In short, celestial geometry is complicated but predictable. Much like many other aspects of the cosmos, it is cyclic.
Need a minute to catch up? Go ahead. We’ll wait. Credit: NASA
Eclipse cycles arise from a natural harmony between three motions of the moon’s orbit. We call them “months” due to their repetitive nature.
The synodic month governs the moon’s phases. It’s measured by the time it takes to go from one new moon to the next, which takes about 29 ½ days. In that time, the moon rotates once around its own axis and goes around Earth once.
From the perspective of a solar eclipse, the new moon phase is important. It’s the point in the moon’s orbit when it passes between Earth and the sun. A total solar eclipse can only happen at a new moon, and only when the other types of movement line up as well.
When the moon, on its orbit around Earth, reaches the point closest to the sun we can’t see the moon reflecting sunlight, so it appears dark. This is the new moon. Credit: NASA/Genna Duberstein
New moons happen once a month, but we don’t see eclipses every month because the moon’s orbit is tipped by about five degrees from Earth’s orbit around the sun. On most months, the new moon casts its shadow either above or below Earth, making a solar eclipse a rare treat.
The moon’s tilted orbit meets the sun-Earth plane at two points called nodes. A draconic month is the time it takes the moon to return to the same node. The moon’s orbital nodes drift over time, which is why a single location on Earth’s surface might wait hundreds of years between total eclipses.
As the moon orbits Earth, it also wobbles up and down, making total eclipses rarer than they otherwise would be. Credit: NASA
The moon’s path around Earth is not a perfect circle, which means the distance between us and the moon changes all the time. When the moon is closest to Earth in its orbit we call it perigee, and apogee when it’s farthest. This change in distance gives rise to the anomalistic month, the time from perigee to perigee.
The farther away the moon is from Earth, the smaller it appears. When the moon blocks all of the sun’s light, a total eclipse occurs, but when the moon is farther away — making it appear smaller from our vantage point on Earth — it blocks most, but not all of the sun. This is called an annular eclipse, which leaves a ring of the sun’s light still visible from around the moon. This alignment usually occurs every year or two, but is only visible from a small area on Earth.
When moon is too small to cover the entire sun’s disk, a ring or “annulus” of bright sunlight surrounds the moon. Credit: NASA/Cruikshank
A total solar eclipse requires the alignment of all three cycles — the synodic, anomalistic, and draconic months. This happens every 18 years 11 days and 8 hours, a period known as a saros.
One saros period after an eclipse, the sun, moon and Earth return to approximately the same relative geometry, a near straight line, and a nearly identical eclipse will occur. The moon will have the same phase and be at the same node and the same distance from Earth. Earth will be nearly the same distance from the sun, and tilted to it in nearly the same orientation.
The extra eight hours is the reason why successive eclipses in the same saros cycle happen over different parts of Earth. Earth rotates an extra third of the way around its axis. Each total solar eclipse track looks similar to the previous one, but it’s shifted 120 degrees westward.
Earth turning on its axis impacts where total solar eclipses occur. Credit: Espenak & Meeus
During this year’s total solar eclipse, anyone within the path of totality will be able to see one of nature’s most awe-inspiring sights. This path, where the moon will completely cover the sun and the sun’s tenuous atmosphere — the corona — can be seen, will stretch from Salem, Oregon to Charleston, South Carolina. Observers outside this path will still see a partial solar eclipse where the moon covers part of the sun’s disk. A total solar eclipse presents the rare opportunity to observe the corona and chromosphere, and eclipse observations are important for understanding why sun’s atmosphere is 1 million degrees hotter than its surface.
Want to find out more about this year’s total solar eclipse — like what totality means and why the path of totality is so much smaller than the overall eclipse? Wonder how long it takes photons from the sun to reach Earth? Curious about dark matter and what we know about it? All are possibilities in the newly revamped Watch the Skies blog.
Hello and welcome back! We will be posting content more regularly, although it will be somewhat changed from before. You can look forward to new articles explaining different astronomy topics, breaking down complex science and jargon in a way that people can understand.
We’ll kick things off this week with some solar eclipse science. So come back then to learn more about just how wonderful and strange our universe can get!
Credit: ESO/José Francisco Salgado
Kevin Matyi is a summer intern in the Office of Communications at NASA’s Marshall Space Flight Center.
There was a very bright green fireball seen by hundreds of eyewitnesses surrounding Lake Michigan early this morning at 1:25:13 AM Central Time (February 6, 2017). The reports from these individuals and the video information from dash cameras and other cameras in the region indicate that the meteor originated 62 miles above West Bend, Wisconsin and moved northeast at about 38,000 miles per hour. It disrupted about 21 miles above Lake Michigan, approximately 9 miles east of the town of Newton. The explosive force of this disruption was recorded on an infrasound station in Manitoba, some 600 miles away – these data put the lower limit energy of the event at about 10 tons of TNT, which means we are dealing with a meteoroid – orbit indicates an asteroidal fragment – weighing at least 600 pounds and 2 feet in diameter. Doppler weather radar picked up fragments (meteorites) falling into Lake Michigan near the end point of the trajectory.
Ground track and Doppler radar signature (done by Marc Fries at NASA Johnson Space Center); an animation of the orbit and approach of the meteoroid is being prepared and should be available soon. We will continue to look at data as it comes in and revise the calculations if necessary.
The Geminids are a meteor shower that occurs in December every year. The best night to see the shower is Dec. 13 into the early hours of Dec. 14. The Geminid meteor shower is caused by a stream of debris left by the asteroid, 3200 Phaethon. When the Earth passes through the trails of dust every December left by 3200 Phaethon, we see the Geminid meteor shower as the dust (meteoroids) burn up in Earth’s atmosphere creating meteors. Geminids travel through Earth’s atmosphere at 78,000 mph and burn up far above the surface.
To observe the Geminids (if it’s not cloudy), get away from bright lights, lay on your back and look up. Let your eyes get adjusted to the dark – you will see more meteors that way. Meteors can generally be seen all over the sky so don’t look in one particular direction. This year’s shower is also on the same night as a full (super) moon so viewing the shower will be more difficult. If you see a meteor, try and trace it backwards. If you end up in the constellation Gemini, there’s a good chance you’ve seen a Geminid.
Given clear weather and dark skies, the Geminid meteor shower can be seen by most of the world, though it is best viewed by observers in the northern hemisphere. This year’s bright moon will wash out all but the brightest Geminids, reducing the rate you can see them significantly. You can expect to see an average of one Geminid every few minutes in dark skies at the shower peak in the northern hemisphere. In the southern hemisphere, the Geminid radiant does not climb very high about the horizon, so observers will see fewer Geminids than their northern counterparts. Most of North America will miss the traditional peak, but because the Geminid activity is broad, good rates will be seen between 10:30 p.m. on Dec. 13 and dawn local time on the morning of Dec. 14. The most meteors should be visible around 2:00 a.m. local time on Dec. 14.
At 2 p.m. CT/3 p.m. ET, engineers & scientists from NASA’s Meteor Environment Office at NASA’s Marshall Space Flight Center will answer questions on the Geminids during a Reddit Ask Me Anything.
If you are in an area with cloudy skies, NASA’s Marshall Space Flight Center will broadcast footage of the shower (pending clear skies here) starting at 8 p.m. Dec. 13 until 6 a.m. on Dec. 14 on Marshall’s Ustream account. You can also see Geminid meteors on NASA’s All Sky Fireball network page. Follow’s NASA’s Meteoroid Environment Office on Facebook for information on meteor showers and fireballs throughout the year.
The annual Geminid meteor shower will peak during the overnight hours of Dec. 13-14, with best viewing typically around 2 a.m. To learn why meteors and comets are important to NASA, the public is invited to join a live Reddit Ask-Me-Anything event at 2 p.m. Dec. 12. Answering your questions will be NASA meteor experts Bill Cooke, Danielle Moser and Rhiannon Blaauw, all from NASA’s Meteoroid Environment Office at NASA’s Marshall Space Flight Center. For viewers experiencing clouds, meteor shower footage will be broadcast live from 8 p.m. Dec. 13 until 6 a.m. on Dec. 14 on Marshall’s Ustream account. Social media followers interested in joining the online conversation can tweet questions to Marshall’s Twitter account or share Geminid images by uploading them to the Geminid Meteor photo group on Marshall’s Flickr account.
On Saturday, Oct. 8, from 5:30 to 9 p.m. the public and media are invited to attend the 6th annual International Observe the Moon Night celebration, hosted by NASA’s Marshall Space Flight Center at the Davidson Center for Space Exploration at the U.S. Space & Rocket Center, both in Huntsville, Alabama.
The free event will include moon-related and solar system exhibits and hands-on activities for children and adults. Activities will include an out-of-this-world photo booth, airbrush tattoo station, and a meet and greet with Janet Ivey from “Janet’s Planet” on PBS. Live music will be provided by DJ Shell. Several large amateur telescopes will be set up to view the moon, stars, and other visible planets. Visitors can also take a virtual 3-D trip to the moon with the astronomy van, offering a magnified, command-module-like view of the lunar surface. The family movie, “Home,” will begin at dusk.
A panel discussion titled: “Planets, Moons & Meteorites Oh My!” will begin at 7:15 p.m. in the National Geographic Theater and will feature Marshall speakers Mitzi Adams, solar physicist; Dr. Barbara Cohen, planetary sceintist; Dr. Bill Cooke, manager of the Meteoroid Environments Office; and Dr. Renee Weber, planetary scientist.
The U.S. Space & Rocket Center is the official visitor center for NASA’s Marshall Space Flight Center.