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HAPPY EQUINOX: Autumn begins in the Northern Hemisphere, and spring in the Southern Hemisphere, today at 4:02 p.m. EDT. That's when the sun crosses the equator heading south for the season. Astronomers call this date the equinox, because night and day are of almost equal length. It also marks the beginning of aurora season. Data prove it: Auroras love equinoxes. At this time of year, even a gentle gust of solar wind can spark a bright display. Free: Aurora Alerts
THE LAST DAY OF SUMMER IN NORWAY: The onset of autumn around the Arctic Circle brings an end to relentless summer sunlight--and a new beginning for Northern Lights. Frank Olsen of Andøya island, Norway, witnessed both on Sept. 21st:
"Last night brought an amazing sunset," says Olsen. "Its glow lasted for hours. A slow-moving aurora band completed the scene with its promise of the season ahead."
That promise could be fulfilled very soon. A solar wind stream flowing from a hole in the sun's atmosphere is heading for Earth. Estimated time of arrival: Sept.23rd or 24th. NOAA forecasters estimate a 40% chance of polar geomagnetic storms when the solar wind arrives. Free: Aurora Alerts
Realtime Aurora Photo Gallery
SPACECRAFT BUZZES EARTH EN ROUTE TO ASTEROID: NASA's OSIRIS-REx spacecraft is flying past Earth today, Sept. 22nd, using our planet's gravity to fling itself toward a potentially hazardous asteroid named "Bennu." At closest approach, OSIRIS-REx will be only 10,711 miles above Earth's surface, inside the orbit of geosynchronous satellites. This map shows the circumstances of the encounter:
During the brief hours around closest approach, the spacecraft could shine with as much reflected sunlight as a 9th to 11th magnitude star--well within reach of backyard telescopes under the ground track. Observing tips are available from NASA.
NASA is visiting Bennu ... before it visits us. Bennu crosses Earth's orbit every six years. In 2135, the asteroid may enter a "keyhole" between the Earth and the Moon where the gravitational pull of our own planet will tweak Bennu's orbit, potentially putting it on course for Earth later that century. Currently, the odds of a collision 150+ years from now are no more than about 1 in 2700--small, but enough to prompt an $800 million space mission.
Arriving in late 2018, OSIRIS-REx will spend more than a year flying in close proximity to Bennu using five instruments to survey the asteroid. The resulting maps will pinpoint a safe sampling site, where the probe can each out with a mechanical arm and gather material from the asteroid's surface. If all goes as planned, samples will be returned to Earth in the Fall of 2023, when a capsule containing bits of Bennu will land at the Utah Test and Training Range.
Realtime Space Weather Photo Gallery
TOTAL ECLIPSE OF THE HEART PENDANTS: On Aug. 21st during the Great American Solar Eclipse, the students of Earth to Sky Calculus launched 11 space weather balloons from the path of totality. They aimed to photograph the Moon's shadow from the stratosphere--and they succeeded. As a fundraiser, some of the balloons carried jewelry, such as this heart-shaped pendant floating inside the Moon's shadow more than 100,000 feet above Oregon's Malheur National Forest:
During the 2.5 hour flight, the pendants were wrapped in the Moon's shadow for more than two minutes, experiencing a spooky darkness colder than -50 C.
You can have one for $149.95. Each limited-quantity pendant comes with a unique gift card showing the jewelry passing through the Moon's shadow and floating at the top of Earth's atmosphere. The interior of the card tells the story of the flight and confirms that this gift has been to the edge of space and back again.
Far Out Gifts: Earth to Sky Store
All proceeds support hands-on STEM education
Every night, a network of
NASA all-sky cameras scans the skies above the United States for meteoritic fireballs. Automated software maintained by NASA's Meteoroid Environment Office calculates their orbits, velocity, penetration depth in Earth's atmosphere and many other characteristics. Daily results are presented here on Spaceweather.com.
On Sep. 22, 2017, the network reported 22 fireballs.
(21 sporadics, 1 Southern Taurid)
In this diagram of the inner solar system, all of the fireball orbits intersect at a single point--Earth. The orbits are color-coded by velocity, from slow (red) to fast (blue). [Larger image] [movies]
Potentially Hazardous Asteroids (
PHAs) are space rocks larger than approximately 100m that can come closer to Earth than 0.05 AU. None of the known PHAs is on a collision course with our planet, although astronomers are finding
new ones all the time.
On September 22, 2017 there were 1803 potentially hazardous asteroids.
|
Recent & Upcoming Earth-asteroid encounters: Asteroid | Date(UT) | Miss Distance | Velocity (km/s) | Diameter (m) |
2017 SP2 | 2017-Sep-17 | 5.9 LD | 22.1 | 27 |
2017 RK2 | 2017-Sep-17 | 2.5 LD | 7.7 | 9 |
2017 RX2 | 2017-Sep-18 | 6.2 LD | 12.6 | 18 |
2017 RU2 | 2017-Sep-18 | 6.8 LD | 8.9 | 25 |
2017 RG2 | 2017-Sep-19 | 7.9 LD | 8.4 | 47 |
2017 SM2 | 2017-Sep-20 | 0.8 LD | 8.5 | 12 |
2017 SR2 | 2017-Sep-20 | 0.2 LD | 10 | 7 |
2017 RQ15 | 2017-Sep-22 | 9.7 LD | 20.4 | 23 |
2017 RB15 | 2017-Sep-22 | 5.8 LD | 5 | 10 |
2017 PR25 | 2017-Sep-23 | 17.9 LD | 13.5 | 228 |
2017 RW2 | 2017-Sep-25 | 15.1 LD | 12.9 | 28 |
2017 SP10 | 2017-Sep-25 | 12.2 LD | 9.2 | 19 |
2017 RW1 | 2017-Sep-25 | 11 LD | 12.7 | 66 |
2017 RO16 | 2017-Sep-25 | 5 LD | 8.2 | 9 |
2017 RB16 | 2017-Sep-26 | 4.8 LD | 9.5 | 26 |
2017 SQ10 | 2017-Sep-27 | 16.2 LD | 7.4 | 18 |
1989 VB | 2017-Sep-29 | 7.9 LD | 6.3 | 408 |
2017 RP15 | 2017-Sep-30 | 14.8 LD | 5.5 | 16 |
2017 OD69 | 2017-Oct-01 | 13.2 LD | 7.6 | 213 |
2017 SO10 | 2017-Oct-04 | 16.7 LD | 8.4 | 37 |
2004 RE84 | 2017-Oct-04 | 15.3 LD | 16.1 | 129 |
2017 RV1 | 2017-Oct-12 | 17.8 LD | 10.9 | 350 |
2012 TC4 | 2017-Oct-12 | 0.1 LD | 7.6 | 16 |
2005 TE49 | 2017-Oct-13 | 8.5 LD | 11.2 | 16 |
2013 UM9 | 2017-Oct-15 | 17 LD | 7.8 | 39 |
2006 TU7 | 2017-Oct-18 | 18.7 LD | 13.3 | 148 |
171576 | 2017-Oct-22 | 5.8 LD | 21.2 | 677 |
2003 UV11 | 2017-Oct-31 | 15 LD | 24.5 | 447 |
444584 | 2017-Nov-17 | 8.7 LD | 14.8 | 324 |
Notes: LD means "Lunar Distance." 1 LD = 384,401 km, the distance between Earth and the Moon. 1 LD also equals 0.00256 AU. MAG is the visual magnitude of the asteroid on the date of closest approach. | Cosmic Rays in the Atmosphere |
Readers, thank you for your patience while we continue to develop this new section of Spaceweather.com. We've been working to streamline our data reduction, allowing us to post results from balloon flights much more rapidly, and we have developed a new data product, shown here:
This plot displays radiation measurements not only in the stratosphere, but also at aviation altitudes. Dose rates are expessed as multiples of sea level. For instance, we see that boarding a plane that flies at 25,000 feet exposes passengers to dose rates ~10x higher than sea level. At 40,000 feet, the multiplier is closer to 50x. These measurements are made by our usual cosmic ray payload as it passes through aviation altitudes en route to the stratosphere over California.
What is this all about? Approximately once a week, Spaceweather.com and the students of Earth to Sky Calculus fly space weather balloons to the stratosphere over California. These balloons are equipped with radiation sensors that detect cosmic rays, a surprisingly "down to Earth" form of space weather. Cosmic rays can seed clouds, trigger lightning, and penetrate commercial airplanes. Furthermore, there are studies ( #1, #2, #3, #4) linking cosmic rays with cardiac arrhythmias and sudden cardiac death in the general population. Our latest measurements show that cosmic rays are intensifying, with an increase of more than 13% since 2015:
Why are cosmic rays intensifying? The main reason is the sun. Solar storm clouds such as coronal mass ejections (CMEs) sweep aside cosmic rays when they pass by Earth. During Solar Maximum, CMEs are abundant and cosmic rays are held at bay. Now, however, the solar cycle is swinging toward Solar Minimum, allowing cosmic rays to return. Another reason could be the weakening of Earth's magnetic field, which helps protect us from deep-space radiation.
The radiation sensors onboard our helium balloons detect X-rays and gamma-rays in the energy range 10 keV to 20 MeV. These energies span the range of medical X-ray machines and airport security scanners.
The data points in the graph above correspond to the peak of the Reneger-Pfotzer maximum, which lies about 67,000 feet above central California. When cosmic rays crash into Earth's atmosphere, they produce a spray of secondary particles that is most intense at the entrance to the stratosphere. Physicists Eric Reneger and Georg Pfotzer discovered the maximum using balloons in the 1930s and it is what we are measuring today.
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