Special Offer: SAVE 600nok per person. Book a combination aurora borealis chase and scenic day tour during the months of September, October or November 2019 for the special price of 1800 kr. Check Marianne's webpage for details!

THE SOLAR WIND HAS ARRIVED: As predicted, a stream of solar wind has reached Earth on July 31st and is gently buffeting our planet's magnetic field. The gaseous material is flowing from a hole in the sun's atmosphere. High-latitude sky watchers should be alert for auroras, especially in the southern hemisphere where winter darkness favors visibility. Aurora alerts: SMS Text.

THE PERSEID METEOR SHOWER IS UNDERWAY: Earth is entering a stream of debris from Comet Swift-Tuttle, source of the annual Perseid meteor shower. Forecasters expect the shower to peak on Aug. 12-13 with many fireballs slicing through the light of a nearly full Moon. It's not even August yet, but NASA's network of all-sky cameras is already detecting a few Perseid fireballs every night--rates which will surely increase in the weeks ahead.

Comet Swift-Tuttle is a giant. It's nucleus is 26 km in diameter, or two-and-a-half times the size of the asteroid that wiped out the dinosaurs. Most other comets are much smaller, with nuclei only a few kilometers across. As a result of its size, Comet Swift-Tuttle produces a large number of meteoroids, many of which are hefty enough to produce fireballs.

Indeed, a 6-year study by NASA's Meteoroid Environment Office found that the Perseids produce more fireballs than any other annual shower:

During the shower, which lasts for weeks, debris particles a few cm wide hit the atmosphere with a speed of 59.6 km/s (133,350 mph). The average magnitude of the resulting fireballs is -3.7, about as bright as Venus.

The luminosity of Perseids is important this year. In 2019 the shower peaks only a few nights before the full Moon, so meteors need to be extra bright to be seen through the glare. Some experts recommend watching a bit earlier than usual, on Aug. 9th, 10th, and 11th when the Moon is less full. The peak nights of Aug. 12th and 13th will be tempered by lunar interference. Whatever night you select, the best time to look is during the hours before sunrise when the shower's radiant is high in the sky. [sky map]

Realtime Space Weather Photo Gallery
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A GOOD NIGHT FOR GREEN AIRGLOW: Nights around the New Moon are special to astrophotographers. They reveal things normally overwhelmed by moonlight. Last night, Ruslan Merzlyakov saw one of those things over Denmark--ripples of green airglow:

"The sky was filled with green airglow," says Merzlyakov. "It crissed-crossed the Milky Way above the island of Møn."

Airglow looks like the aurora borealis, but it is not the same. Airglow is caused by a complex assortment of chemical reactions in Earth's upper atmosphere. These reactions get started during daylight hours when the atmosphere is bathed in strong UV radiation from the sun.  At night we see the afterglow, colored green by oxygen atoms 90-100 km high or sometimes red by hydroxyl ions 86-87 km high.

"The airglow was corrugated by gravity waves propagating upward from a nearby thunderstorm," adds  Merzlyakov.  This phenomenon is quite common during the season for summer storms, and gives most airglow a dramatic rippling structure.

"Now I can't wait for the first Perseids!" he says.

THE STARSHIP ENTERPRISE IN THE STRATOSPHERE: Last week, the students of Earth to Sky Calculus launched the starship Enterprise to the stratosphere. Riding onboard a high-altitude cosmic ray balloon, the laser-etched crystal spaceship traveled 34.7 km (113,845 feet) above Earth's surface:

You can have it for $149.95. The students are selling the Enterprise to support their cosmic ray ballooning program. Each starship comes with a greeting card showing the item in flight and telling the story of its journey to the edge of space. Also included is a multi-colored LED illuminated stand (shown in the picture above). This creates a colorful visual effect and allows the Enterprise to be used as a far-out night light.

Far Out Gifts: Earth to Sky Store
All sales support hands-on STEM education

Realtime Aurora Photo Gallery
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On Jul. 31, 2019, the network reported 36 fireballs.
(25 sporadics, 7 Southern delta Aquariids, 3 Perseids, 1 alpha Capricornid)

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]

Recent & Upcoming Earth-asteroid encounters:

Asteroid	Date(UT)	Miss Distance	Velocity (km/s)	Diameter (m)
2010 PK9	2019-Jul-26	8.2 LD	16.5	155
2019 NT1	2019-Jul-27	19 LD	3.7	14
2019 OD3	2019-Jul-28	0.5 LD	18.1	15
2019 OM3	2019-Jul-28	2.6 LD	12.8	18
2019 OB1	2019-Jul-28	2 LD	6.9	9
2019 ON3	2019-Jul-29	0.6 LD	14.2	10
2019 NN4	2019-Jul-29	6.6 LD	3.8	26
2019 ON	2019-Aug-01	6.8 LD	4.7	33
2019 OJ3	2019-Aug-02	11.4 LD	16.2	60
2006 QQ23	2019-Aug-10	19.4 LD	4.7	339
454094	2019-Aug-12	17 LD	8.2	148
2018 PN22	2019-Aug-17	17.1 LD	2.3	11
2016 PD1	2019-Aug-26	11.4 LD	5.9	65
2002 JR100	2019-Aug-27	19.4 LD	8.4	49
2019 OU1	2019-Aug-28	2.7 LD	13.2	92
2019 OF2	2019-Sep-03	18 LD	10.5	49
2018 DE1	2019-Sep-03	12.7 LD	6.6	28
2019 GT3	2019-Sep-06	19.5 LD	13.6	227
2010 RM82	2019-Sep-13	18.2 LD	14.6	23
2013 CV83	2019-Sep-13	15.7 LD	13.1	62
504800	2019-Sep-14	13.9 LD	14.4	155
467317	2019-Sep-14	13.9 LD	6.4	389
2019 JF1	2019-Sep-16	11.2 LD	4.3	61
2018 FU1	2019-Sep-16	18.4 LD	4.7	16
2017 SL16	2019-Sep-21	7.9 LD	6.5	25
2017 SM21	2019-Sep-21	11.5 LD	9.6	20
2006 QV89	2019-Sep-23	15.9 LD	4.2	31
523934	2019-Sep-24	10.9 LD	22.3	257
2017 KP27	2019-Sep-26	6.2 LD	4.8	25

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

SOMETHING NEW! We have developed a new predictive model of aviation radiation. It's called E-RAD--short for Empirical RADiation model. We are constantly flying radiation sensors onboard airplanes over the US and and around the world, so far collecting more than 22,000 gps-tagged radiation measurements. Using this unique dataset, we can predict the dosage on any flight over the USA with an error no worse than 15%.

E-RAD lets us do something new: Every day we monitor approximately 1400 flights criss-crossing the 10 busiest routes in the continental USA. Typically, this includes more than 80,000 passengers per day. E-RAD calculates the radiation exposure for every single flight.

The Hot Flights Table is a daily summary of these calculations. It shows the 5 charter flights with the highest dose rates; the 5 commercial flights with the highest dose rates; 5 commercial flights with near-average dose rates; and the 5 commercial flights with the lowest dose rates. Passengers typically experience dose rates that are 20 to 70 times higher than natural radiation at sea level.

To measure radiation on airplanes, we use the same sensors we fly to the stratosphere onboard Earth to Sky Calculus cosmic ray balloons: neutron bubble chambers and X-ray/gamma-ray Geiger tubes sensitive to energies between 10 keV and 20 MeV. These energies span the range of medical X-ray machines and airport security scanners.

Column definitions: (1) The flight number; (2) The maximum dose rate during the flight, expressed in units of natural radiation at sea level; (3) The maximum altitude of the plane in feet above sea level; (4) Departure city; (5) Arrival city; (6) Duration of the flight.

SPACE WEATHER BALLOON DATA: 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 18% since 2015:

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.

En route to the stratosphere, our sensors also pass through aviation altitudes:

In this plot, 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.

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.

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.

Essential web links

NOAA Space Weather Prediction Center

The official U.S. government space weather bureau

Atmospheric Optics

The first place to look for information about sundogs, pillars, rainbows and related phenomena.

Solar Dynamics Observatory

Researchers call it a "Hubble for the sun." SDO is the most advanced solar observatory ever.

STEREO

3D views of the sun from NASA's Solar and Terrestrial Relations Observatory

Solar and Heliospheric Observatory

Realtime and archival images of the Sun from SOHO.

Daily Sunspot Summaries

from the NOAA Space Environment Center

NOAA 27-Day Space Weather Forecasts

fun to read, but should be taken with a grain of salt! Forecasts looking ahead more than a few days are often wrong.

Aurora 30 min forecast

from the NOAA Space Environment Center

Heliophysics

the underlying science of space weather

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