In the mythology of ancient Egypt, Apep was the serpent god — the rival of Re, the sun god. He chased Re, and sometimes briefly caught him — creating a solar eclipse.
NASA plans to launch an experiment named for the serpent god to study the eclipse on Monday. Instruments will fly on three different rockets. They won’t look at the Sun, though. Instead, they’ll study the effect of the eclipse on the ionosphere — a high-altitude layer of Earth’s atmosphere.
The ionosphere carries an electric charge. It “bends” radio waves, allowing them to travel far around the planet. During the day, sunlight intensifies the charge. At night, the charge lessens.
Scientists want to understand how the ionosphere reacts to the brief loss of sunlight during an eclipse. That should tell them more about the ionosphere overall, and how it changes during the day.
Among other ways, they’ll do so by launching Apep. Three small rockets will take flight from a NASA center in Virginia. The rockets will climb about 200 miles high. They’ll deploy several instruments, which will make observations for seven or eight minutes. Then they’ll parachute back to Earth.
The same instruments flew during last year’s annular eclipse, when the Moon didn’t fully cover the Sun. This year’s flights will allow scientists to compare the results — learning more about how Earth’s atmosphere reacts when the Sun grows darker.
More about the eclipse tomorrow.

Eclipse Flights

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Astronomy

Over the centuries, no planet has been as frustrating to study as Mercury. The Sun’s closest planet never moves far from the Sun in our sky. So when astronomers pointed telescopes at Mercury, it was almost always screened by twilight and a thick layer of Earth’s atmosphere. So most of what we know about Mercury has come from spacecraft that visited the planet.



You can see the difficulty yourself the next few days. Mercury is quite low in the east not long before sunrise. It’s almost at its farthest point from the Sun, and it looks like a fairly bright star. But at that low altitude, its light has to pass through a thick layer of air, which blurs the view. The glow of twilight makes the view even murkier.



Without the ability to see surface features, it was hard to nail down the length of Mercury’s day. The planet always shows the same face when it’s closest to Earth. So it looked like Mercury was locked so that the same hemisphere always faced the Sun, just as the same side of the Moon always faces Earth.



But that’s not right. Radio telescopes have showed that Mercury makes three turns on its axis for every two orbits around the Sun. That means a “day” on Mercury — the time from one noon to the next — lasts 176 Earth days — long days and nights for the Sun’s closest planet.



Mercury appears near the Moon the next couple of mornings. It’s to the lower left of the Moon tomorrow, and closer to the right on Monday.



Script by Damond Benningfield

Moon and Mercury

The atmosphere of Mars is quite different from Earth’s. It’s colder, thinner, and it’s made mainly of carbon dioxide. In one way, though, the skies of the two planets are similar: both of them have clouds. And for the most part, the clouds themselves are alike as well.



Because Mars is so cold, the clouds are made entirely of ice — frozen water or carbon dioxide. There’s not much water in the Martian atmosphere, so the clouds are thin. And they’re usually much higher than even the highest clouds of Earth.



But Mars also has some clouds that are a bit different from those on Earth. That includes “dots” and some long, skinny ribbons.



An orbiting spacecraft has seen the dots in a specific region of Mars, south of the equator. The clouds are almost perfectly round. They’re up to 60 miles in diameter, a few miles thick, and they top out at altitudes of 30 to 50 miles. Some are seen at dawn, while others are seen in clumps in the dawn or evening twilight. The clouds could form as the atmosphere interacts with some odd spots in the Martian magnetic field.



The elongated clouds are seen in volcanic regions. The longest span about 1500 miles, and are up to a hundred miles wide. They may be sculpted by winds flowing over volcanic peaks — some odd clouds for the Red Planet.



Mars stands close to the lower left of the Moon at dawn tomorrow. The planet Saturn is about the same distance to the upper right of the Moon.



Script by Damond Benningfield

Moon and Planets

The solar system is pretty settled. The planets appear to be following orbits that have remained stable for billions of years. But in the early days, things might have been a lot more chaotic. According to one model, in fact, the giant planets Jupiter and Saturn might have moved much closer to the Sun before they moved back out again.



The planets probably took shape from a disk of gas and dust around the Sun. Small bits of material stuck together to make bigger bits, all the way up to planets. But much of the material remained free. There was enough of it to exert both a drag and a pull on the giant planets.



In this model, Jupiter — the Sun’s heaviest planet — was born at about two-thirds of its present distance from the Sun. It quickly moved inward, though, all the way to the orbit of Mars. Saturn — the second-most-massive planet — was dragged inward as well. Jupiter and Saturn thinned out the supply of gas and dust and the leftover planetary building blocks — either by scooping them up or kicking them away from the Sun. That changed the gravitational balance of the solar system. Jupiter and Saturn moved outward — settling into their current stable orbits around the Sun.



Saturn is in the dawn sky now, and looks like a bright golden star. Unlike a star, though, it doesn’t twinkle — its light holds steady. Tomorrow, it will stand close to the left of the Moon. The Moon will pass between Saturn and Mars the next morning; more about that tomorrow.



Script by Damond Benningfield

Moon and Saturn

One of the larger moons of the planet Neptune has been through a lot. It might have started as an asteroid, and was captured by Neptune’s gravity. Or it might have started as a moon, but was hurled into a wild orbit when Neptune grabbed its largest moon. And since then, it’s been battered by impacts with other space rocks.



Nereid was discovered 75 years ago today, by Gerard Kuiper. It was only the second moon seen around the giant planet, and it’s the third-largest of Neptune’s 16 known moons.



Kuiper was observing Neptune with the 82-inch telescope at McDonald Observatory. In a pair of 40-minute exposures, the moon showed up as a tiny star near the planet. Kuiper suggested the name Nereid because, in mythology, the Nereids were daughters of Neptune.



We don’t know a lot more about the moon today than when it was discovered. It’s more than 200 miles in diameter, its gray surface probably is coated with ice and rock, and the surface is rough — perhaps the result of billions of years of impacts.



Nereid follows the most lopsided orbit of any good-sized moon in the solar system. It ranges from less than a million miles from Neptune to about six million miles. That suggests that Nereid could be the last of Neptune’s original moons. When Neptune captured its biggest moon, Triton, Triton’s gravity could have kicked out all the others, leaving only Nereid — in a wild orbit around a giant planet.



Script by Damond Benningfield

Nereid

Earth’s magnetic field sometimes does a flip. The north magnetic pole becomes the south pole, and vice versa. On average, it happens once every few hundred thousand years.
But sometimes, it’s more of a flip flop — the field flips right back over.
One flip-flop took place about 42,000 years ago. Known as the Laschamps Excursion, the flip lasted only a few hundred years. And a recent study said the transition could have been a major problem for Earth’s environment.
The magnetic field protects us from radiation from the Sun and beyond. As the field flips, though, it gets weaker. That allows more radiation to reach the upper atmosphere, where it can zap the ozone layer. In turn, that allows more radiation to reach the surface, where it can cause skin cancers, mutations, and other problems.
During the Laschamps era, the magnetic field dropped to only a few percent of its current strength. Scientists studied the effect of that drop by examining trees buried in New Zealand. The trees’ annual growth rings contained high levels of radioactive carbon — an indication that more radiation was reaching the surface.
The researchers said that the weaker field could have been related to major climate changes, including animal extinctions in Australia.
No other research has reported such dramatic impacts from a flip. So it’s unclear what effect the next flip — or flip-flop — might have on life on our planet.
Script by Damond Benningfield

Eclipse Flights

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