StarDate

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.
The special sunset alignment occurs twice per year, about three weeks before and after the summer solstice, in June.

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

Lightning may flash through the skies of Mars. But don’t expect to see big, jagged streaks like those produced by storms on Earth. Instead, they may be tiny sparks – like fireflies twinkling through a summer evening.

On Earth, lightning is generated by the motions of bits of ice inside clouds. As the particles move past each other, they build up an electric charge. They dis-charge as lightning.

The clouds on Mars are high and thin, so there’s no way for them to make big lightning bolts. But the dust grains that swirl through the Martian atmosphere might generate their own discharges. And two recent studies found evidence of them.

In the first, researchers combed through recordings made by a microphone on the Perseverance rover. They found 55 instances of small “crackling” sounds near the rover. Almost all of them happened during dust storms, or when small dust devils passed the rover.

The scientists decided the most likely explanation for the crackles was tiny discharges – “lightning” bolts about a centimeter long.

In the second study, a team looked at observations made by the MAVEN orbiter. The scientists looked for radio waves produced by lightning, which are different from other types of radio from the planet. They found a single example – a possible flicker in Martian skies.

Even if lightning is small and rare, it could interfere with future Mars landers – perhaps endangering instruments and people on the Red Planet.

Script by Damond Benningfield