StarDate

The night sky can sometimes look like a tie-dyed T-shirt flapping on a clothesline. Ribbons and swirls of bright color ripple through the sky. They can change appearance in seconds – blown by the solar wind.

The colorful display is an aurora – the northern and southern lights. An aurora flares to life as charged particles from the Sun run into Earth at high speed.

Earth’s magnetic field funnels the particles toward the magnetic poles. When particles hit atoms and molecules high above the surface, they knock atoms out of their usual configuration. When they return to normal, the atoms emit light.

The color of an aurora depends on what the charged particles hit, and where they hit it. Most auroras are green. They switch on when particles hit oxygen molecules at altitudes of about 60 to 200 miles. Red auroras are fed by oxygen that’s even higher.

The lower fringes of a display can appear pink or dark red – the result of collisions with nitrogen at lower altitudes. Collisions with hydrogen and oxygen create blue and purple auroras. But they’re not very common, and they’re hard for the eye to take in. They’re easier to see in photographs.

Most of the time, the northern lights stay close to the magnetic pole. When the Sun spews out more particles, though, they can spread outward, shining in regions where they’re seldom seen. And the colors can get more intense – dramatically “tie-dying” the night sky.

Script by Damond Benningfield

The goddess of the dawn has given millions of Americans a rare treat the past couple of years: brilliant displays of the northern lights in regions where they’re seldom seen. Today, we know that these colorful curtains of light are powered by storms on the Sun. Bigger storms expand the viewing area. But in centuries past, cultures around the globe created their own explanations.

In Scandinavia, for example, the northern lights might have represented Bifrost, the “rainbow bridge” that connected Earth to Asgard, the home of the gods. In some of the islands of Scotland, the lights represented a pair of chieftains fighting for the hand of a “merry dancer.”

In southern England, they were considered omens of misfortune. Some saw the lights as clashing swords; red lights were streamers of blood. During an intense outburst in March 1716, at the end of a civil war, people ran into the streets in their nightclothes, and some thought it was judgment day. One writer said that some “read in its glaring visage, the fate of nations and the fall of kingdoms.”

The name for the northern lights – the aurora borealis – was bestowed in 1619 by Italian astronomer Galileo Galilei. Aurora was the Roman goddess of the dawn. Boreas was the Greek god of storms and the north wind – one of the namesakes of the always beautiful, sometimes frightening northern lights.

More about the aurora tomorrow.

Script by Damond Benningfield

Sixty years ago today, NASA was making its first attempt to land on the Moon.

The robotic lander touched down in a crater in the Ocean of Storms – a giant volcanic plain. It was a precursor to the Apollo missions, which would land astronauts on the Moon.

Surveyor wasn’t the first probe to land on the Moon – a Soviet mission beat it by a few months. But Surveyor was more sophisticated. It carried a television camera to beam back images of its surroundings.

Surveyor transmitted its first pictures just minutes after landing. And during its first lunar “day” – almost 14 Earth days – it snapped more than 10 thousand images. They showed a surface coated with small rocks, and pockmarked by small craters. The rim of the crater Surveyor landed in was visible in the distance.

Pictures of its landing pads revealed important details about the texture of the lunar surface, as this NASA documentary pointed out:

 ANNOUNCER: The lunar surface texture not thick layers of loose dust into which spacecraft or men could sink. In the area of the Ocean of Storms, man can land and walk on the lunar surface.

Surveyor 1 survived the frigid lunar night, taking hundreds more pictures the next day. Scientists even raised it the following January – seven months after its historic landing on the Moon.

Script by Damond Benningfield

The twins of Gemini have a front-row seat for a planetary waltz this month. Venus, Jupiter, and Mercury are close to the twins now, and will bunch up even closer as the month progresses.

The “twins” are the stars Pollux and Castor. They’re about a quarter of the way up the western sky as evening twilight fades. Pollux is the brighter of the two, with Castor to its right.

Jupiter looks like a brilliant star to the lower left of the twins. It’s the largest planet in the solar system. But it’s on the far side of the Sun as seen from Earth, so it’s more than 550 million miles away – about six times the distance between Earth and the Sun.

Venus is even brighter – the “evening star.” It’s below the twins. Although it’s a little smaller than Earth, it shines much brighter than Jupiter mainly because it’s much closer to both Earth and the Sun.

Venus and Jupiter remain in view for a good while after darkness falls. That’s not the case for Mercury. It’s well to the lower right of the others, and much lower in the sky. It’s bright, though, so with a clear horizon, there’s a good chance to spot it.

Mercury will move a little higher into the sky over the next few nights, improving the view. But the real action involves Jupiter and Venus. Venus is climbing away from the Sun quickly. It will nestle especially close to Jupiter on the 8th and 9th. It’ll pull away after that – all in close view of the twins.

Script by Damond Benningfield

It’s early in the long winter night at the south pole. But a few dozen scientists and others have settled in at a research base there. They monitor the weather and climate, listen to rumbles in the ice below, and watch auroras dancing in the dark skies above. And they operate observatories that study the universe beyond.

One of those observatories is buried in the ice. Known as IceCube, it’s a set of thousands of light detectors. They look for evidence of neutrinos – particles that are produced in the Sun, exploding stars, and other powerful objects and events. They almost never interact with other matter. But when one does interact, by smashing into an ice molecule, it produces a quick flash of light. Studying that flicker reveals details about the neutrino, including its origin. And that tells scientists more about the body that created it.

Another observatory, the South Pole Telescope, studies the “afterglow” of the Big Bang. Known as the cosmic microwave background, it’s a sort of “haze” that fills the entire universe. Tiny fluctuations in the haze reveal details about the birth of the first stars and galaxies.

Water vapor in the atmosphere absorbs microwaves. But the south pole is almost two miles high, and it’s so cold that there’s almost no water vapor in the skies above it. That allows the 10-meter dish to study the background glow in great detail – under the clear, dark skies at the bottom of the world.

Script by Damond Benningfield

The Moon can be like a painter’s canvas, dabbed with many colors: the silver of a frosty night, the gold of honey, the orange of a ripe cantaloupe, even the deep red of blood. But it’s almost never blue – at least not in appearance. It sometimes is blue in name, though – including tonight. That’s because it’s the second full Moon of May – a repeat appearance known as a Blue Moon.

The color of the Moon – full or not – depends on several factors. When the Moon is low in the sky, as it rises or sets, its light passes through a thicker layer of air. Molecules in the atmosphere scatter blue wavelengths of light, allowing the red to shine through.

As the Moon climbs higher, we see more of its true color – gray. But the Moon is so bright that it looks white or silver.

During a lunar eclipse, the Moon passes through Earth’s dark shadow. But sunlight filtering through Earth’s atmosphere makes the Moon look dark orange or red.

In rare cases, the Moon can actually look blue. That happens after volcanic eruptions or big forest fires. These events pump out particles that scatter red light, allowing the blue to shine through. After the eruption of Krakatoa, in 1883, the Moon appeared blue for months around the entire globe.

Whatever its color, enjoy tonight’s Blue Moon. And look quite close to it throughout the night for the star Antares, the heart of the scorpion. They’ll be closest as they set.

Script by Damond Benningfield

For most American skywatchers, the star Capella is just peeking into view in the morning twilight. It’s bright, but it’s quite low as the sky brightens. You need precise timing and a clear north-northeastern horizon to spot it.

A star’s first appearance is called the heliacal rising – a term that means “with the Sun.” It takes place at the same time every year, as the Sun completes a full circuit through the background of stars.

In many ancient cultures, the heliacal rising of certain stars was crucial. The best example is Sirius, the brightest star in the night sky. In Egypt, it first appeared just before the annual flooding of the Nile – the most important event of the year. So the star’s return marked the start of a new year.

Several cultures looked for the Pleiades star cluster. Its appearance marked a time to plant crops, or to gather them, depending on a culture’s location.

Capella might have been important to the Zapotec, who lived in present-day Mexico. A half-century ago, researchers proposed that a building in the city of Monte Albá‡n was intentionally aligned at a right angle to Capella’s rising point. The star first appeared there at the time the Sun passed directly overhead at noon – a key date in the calendar. But later work disputed that finding.

Capella isn’t nearly as important in modern times. But it reminds us that the stars once held great power over much of everyday life.

Script by Damond Benningfield

Thousands of New Yorkers and visitors will crowd the major east-west streets of Manhattan the next couple of afternoons – all to watch the setting Sun. Weather permitting, the Sun will be perfectly framed by the island’s urban canyons as it descends over the Hudson River.

The event is known as Manhattanhenge. It’s named for Stonehenge, the ancient monument in England. Its stones appear to have been aligned with key sunrise and sunset points, and other events.

Manhattan produces its own alignments. The island is laid out in a perfect grid, and there are no obstructions along the horizon to block the Sun.

Today, the Sun will be half above and half below the horizon at the peak viewing time. Tomorrow, the full solar disk will stand directly atop the horizon. That sequence is reversed on the nights of July 12th and 13th.

Manhattanhenge has become a popular tourist attraction. The streets are clogged by a half hour before sunset. And some venues hold special events to celebrate the view.

New York isn’t the only city where you can see the Sun setting between the buildings. But few offer the same alignment of streets and the open horizon provided by Manhattan.

Script by Damond Benningfield

The star Vega is a bit of a puzzler. Over the years, astronomers reported evidence of several planets orbiting the bright star. But none of the planets has been confirmed. And observations by two space telescopes revealed nothing. But they left open the possibility of planets.

Vega is low in the east-northeast at nightfall, and soars high overhead later on. It’s about 25 light-years away. It’s a bit bigger, brighter, and heavier than the Sun. And it’s younger – just 10 percent the Sun’s age.

A disk of dust encircles Vega. It’s tens of billions of miles wide. Hubble Space Telescope recently found a “halo” of tiny dust grains that extends tens of billions of miles beyond the disk.

Hubble and James Webb Space Telescope took a good look at the system. They showed that the disk is quite smooth. It’s probably renewed by comets and asteroids. They shed material as they orbit the star, and even more when they slam together. The smoothness of the disk means there are no giant planets orbiting within it. If there were, they would clear out wide gaps.

There is one gap. But it’s not completely open. So a planet several times the mass of Earth could orbit in that zone, partially clearing it out. And there could be smaller planets elsewhere in the system – especially close to Vega. But so far, there are no confirmed planets – leaving Vega to travel through space alone.

Script by Damond Benningfield

On September 1st of 1859, Richard Carrington was studying the Sun, as he did every day. The British astronomer used a small telescope to project an image of the Sun on a screen. That allowed him to map the dark features known as sunspots.

But on this day, Carrington saw something he’d never seen before. Bright features mingled with the sunspots. They were the first solar flares ever recorded – and still the most powerful. So the outburst is called the Carrington Event in his honor. Carrington also linked the flares to brilliant auroras seen across the globe the following day – the first observations of space weather.

Carrington was born 200 years ago today, in London. He originally studied theology, but became hooked on astronomy. He joined an observatory, but left after a couple of years. He built his own observatory, in Surrey.

Carrington watched the skies both day and night. He compiled star catalogs. And he made the most impressive studies of the Sun to that time, revealing some crucial details about the Sun. For one thing, it rotates faster near its poles than at the equator. For another, during the 11-year sunspot cycle, the spots move from middle latitudes to near the equator.

Carrington eventually had to give up his research. When his father died, he had to take over the family brewery. His health failed as well. He died in 1875 – a pioneer at studying the Sun.

Script by Damond Benningfield