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NOCTILUCENT CLOUDS OVER LONDON: On the summer solstice, a midnight display of noctilucent clouds (NLCs) startled sky watchers in London, who could see tendrils of frosted meteor smoke glowing through the city's urban lights. The outbreak over London is a sign that even more intense NLCs are on the way. Indeed, they have already spread to multiple states in the USA including Washington, Oregon, and Idaho. Browse: photo gallery.

MASSIVE SAHARA DUST CLOUD WIPES OUT THE NIGHT SKY: A cloud of dust just swallowed Puerto Rico. "For the past two days, dust from the Sahara desert has filled the air here in the Caribbean," reports Frankie Lucena of Cabo Rojo, Puerto Rico. "I've seen plenty of Saharan dust events, and this is by far the worst one yet. It has completely blocked out most of the stars in our night sky." He took this picture near local midnight on June 21-22:

"Only Jupiter and Saturn (and the Lajas Aerostat) were relatively easy to see," he says. "I wonder if dust storms on Mars would have a similar color if photographed at night."

The dust enveloping Puerto Rico is coming from the Sahara desert thousands of miles away. In a sense, this is nothing unusual. Every year, hundreds of millions of tons of African dust cross the Atlantic. Migrating dust helps build beaches in the Caribbean and fertilizes soils in the Amazon. It can also desiccate thunderclouds and suppress storms. Satellites track African dust meandering over the Caribbean every June and July.

But this particular dust plume is epic--perhaps the most massive in half a century. "Today (June 23rd) we registered the highest level of Saharan Dust in 20 years of data," says Lucena. "Meteorologists also indicated that air quality was at its highest warning level. Many folks in my area decided to stay indoors."

Above: Satellite images show Saharan dust overrunning Puerto Rico, June 18-22. [more]

Later this week, on Thursday or Friday, the dust plume is expected to reach Texas. It won't be as dense as it was in Puerto Rico, but Texans will notice its arrival, bringing milky daytime skies along with vivid sunrises and sunsets. On Saturday, the plume could turn east and drift over southern and mid-Atlantic US states. Got photos? Submit them here.

Realtime Space Weather Photo Gallery
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COMET NEOWISE IS LOOKING GOOD: Comet NEOWISE (C/2020 F3) is plunging toward the sun for a close encounter near the orbit of Mercury on July 3rd. SOHO coronagraphs are monitoring the approach, and it's looking good:

The sun-baked comet is still intact. Moreover, comparing the comet to nearby reference stars, we see that it is brightening to approximately magnitude +3. This should make Comet NEOWISE a naked-eye object when it emerges from the sun's glare in mid-July. SOHO will be monitoring the comet for the rest of the week, so stay tuned for updates.

Realtime Comet Photo Gallery
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APOLLO 11 PROOF SILVER DOLLAR (COLLECTOR'S ITEM): Are you looking for a far-out gift? Consider this: On July 20, 2019 (the 50th anniversary of the Apollo 11 Moon landing), the students of Earth to Sky Calculus flew this rare proof silver dollar to the stratosphere:

The US Mint created the coins to celebrate the first Moon landing--but you can no longer buy them from the Mint. You can, however, get one from Earth to Sky Calculus. The students are selling the collector's item for $229.95 to support their cosmic ray ballooning program.

The silver dollar is curved and reproduces the helmet of astronaut Buzz Aldrin. Reflected in Buzz's visor are Neil Armstrong, the United States flag, and the lunar lander. The opposite side of the coin shows Neil's iconic footprint on the Moon. Included is a greeting card showing the coin in flight and a certificate of authenticity.

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

Realtime Aurora Photo Gallery
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On June 24, 2020, the network reported 12 fireballs.
(12 sporadics)

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)
2018 PD22	2020-Jun-19	17.2 LD	14.6	56
2020 KR1	2020-Jun-22	11.6 LD	6.8	41
2020 LV	2020-Jun-22	5.4 LD	4.8	31
2020 MS1	2020-Jun-23	19.5 LD	12.7	78
441987	2020-Jun-24	9.8 LD	12.9	186
2020 MP1	2020-Jun-25	1.2 LD	7.8	23
2017 FW128	2020-Jun-25	6.9 LD	5.4	11
2020 MA	2020-Jun-25	5.3 LD	7.8	31
2020 MK	2020-Jun-27	12 LD	17.8	116
2020 MF1	2020-Jun-27	1.3 LD	10.5	10
2020 KQ7	2020-Jun-27	10.3 LD	2.6	18
2020 ME1	2020-Jun-28	2 LD	10.9	21
2020 JX1	2020-Jun-29	3.3 LD	5	62
2019 AC3	2020-Jul-01	10.5 LD	3.4	12
2020 MO	2020-Jul-03	9.3 LD	9.6	41
2007 UN12	2020-Jul-04	16.7 LD	2.9	6
2020 LS	2020-Jul-04	19.4 LD	11.6	74
2020 MU1	2020-Jul-11	18.8 LD	2.7	38
2020 ML	2020-Jul-12	11.4 LD	4.4	23
2020 KJ7	2020-Jul-13	11.9 LD	3.4	30
2009 OS5	2020-Jul-13	17.6 LD	2.6	45
2020 MX	2020-Jul-17	15.1 LD	5.4	53
2016 DY30	2020-Jul-19	9 LD	15.1	3
2002 BF25	2020-Jul-21	9.4 LD	6.8	129
2018 PY7	2020-Jul-31	8.9 LD	9.5	16
2007 RF1	2020-Jul-31	10.7 LD	5	21
2018 BD	2020-Aug-03	7.6 LD	9.4	3
2009 PQ1	2020-Aug-05	10.8 LD	13.5	112

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 Regener-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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