By Kevin Matyi
By Kevin Matyi
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.
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.
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.
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.
For more information on the eclipse, where to view it and how to view it safely (wear eye protection!), visit https://eclipse2017.nasa.gov/sun.
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!
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.
Links to videos of this event:
Lisle, IL Police Department
From Highway in Wisconsin:
Chillicothe IL Police Department:
Morton Grove Police Squad
Roof of Atmospheric, Oceanic & Space Sciences Building – University of Wisconsin https://www.youtube.com/watch?v=LHubXCtdEbo
Looking over Lake Michigan, from Michigan Coast: (looking too north to see the meteor itself) http://www.earthcam.com/usa/michigan/grandhaven/lakemichigan/?cam=lakemichigan
Bright flash at 2:25:13
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.
For more information on NASA’s Marshall Space Flight Center, visit https://www.nasa.gov/centers/marshall/home/index.html.
For more information on the U.S. Space & Rocket Center, visit http://rocketcenter.com.
Make plans now to stay up late or set the alarm early next week to see a cosmic display of “shooting stars” light up the night sky. Known for it’s fast and bright meteors, the annual Perseid meteor shower is anticipated to be one of the best potential meteor viewing opportunities this year.
The Perseids show up every year in August when Earth ventures through trails of debris left behind by an ancient comet. This year, Earth may be in for a closer encounter than usual with the comet trails that result in meteor shower, setting the stage for a spectacular display.
“Forecasters are predicting a Perseid outburst this year with double normal rates on the night of Aug. 11-12,” said Bill Cooke with NASA’s Meteoroid Environments Office in Huntsville, Alabama. “Under perfect conditions, rates could soar to 200 meteors per hour.”
An outburst is a meteor shower with more meteors than usual. The last Perseid outburst occurred in 2009.
How to Watch the Perseids
The best way to see the Perseids is to go outside between midnight and dawn on the morning of Aug. 12. Allow about 45 minutes for your eyes to adjust to the dark. Lie on your back and look straight up. Increased activity may also be seen on Aug. 12-13.
For stargazers experiencing cloudy or light-polluted skies, a live broadcast of the Perseid meteor shower will be available via Ustream overnight on Aug. 11-12 and Aug. 13-14, beginning at 10 p.m. EDT.
Read more about the Perseids here.
For a few seconds early Thursday, night turned into day as an extremely bright fireball lit the pre-dawn sky over much of Arizona, blinding all-sky meteor cameras as far away as western New Mexico.
Based on the latest data, a small asteroid estimated at 5 feet (1-2 meters) in diameter – with a mass of a few tons and a kinetic energy of approximately half a kiloton – entered Earth’s atmosphere above Arizona just before 4 a.m. local (MST) time. NASA estimates that the asteroid was moving at about 40,200 miles per hour (64,700 kilometers per hour).
Video obtained from the NASA meteor camera situated at the MMT Observatory on the site of the Fred Lawrence Whipple Observatory, located on Mount Hopkins, Arizona, in the Santa Rita Mountains.
Read more here.
We observed a fireball the morning of May 4 around 12:50am EDT, traveling southwest at about 77,000 mph over the Nantahala National Forest on the Tennessee/North Carolina state line. At its brightest point, it rivaled the full moon. According to Dr. Bill Cooke in NASA’s Meteoroid Environment Office at NASA’s Marshall Space Flight Center in Huntsville, Ala. , “The fireball was bright enough to be seen through clouds, which is an attention getter. In Chickamauga, Ga., one would have thought it was a flash of lightning lighting up the clouds beneath.”