StarDate Billy Henry

For many countries in Europe, today is Midsummer Day. It’s marked with bonfires and other celebrations. It marks the middle of summer, which began back in May.
Astronomically, though, today marks the start of summer in the northern hemisphere. It’s the summer solstice — the longest day of the year. It marks a turning point for the Sun, which will begin to move southward after today.
Regardless of whether it was considered the start of summer or its middle, the solstice had great significance for cultures around the world. They held festivals and religious ceremonies to celebrate the light.
Many cultures used natural alignments to track the Sun’s motions along the horizon, allowing them to pinpoint the date. They also made their own alignments.
One of the most famous examples is Stonehenge in England. But there are plenty of examples in the Americas as well.
In the United States, many are still found in the southwest, in the remnants of ancient pueblo sites. Many of the solstice markers are spirals carved or painted on rock surfaces. The rising Sun passes through cracks or notches in the nearby rocks, creating daggers of light across the spirals.
Other markers were built into houses or ceremonial structures. Narrow windows, for example, might allow the sunlight to shine onto symbols on the opposite wall — symbols dedicated to the rising Sun on the summer solstice.
We’ll have more about the solstice tomorrow.
Script by Damond Benningfield

You might think that astronomers would know just about everything there is to know about the brighter stars in the night sky. That’s not the case, though. In fact, some of those stars can be especially vexing.
An example is Antares, the orange supergiant that marks the heart of Scorpius, the scorpion. The star huddles quite close to the Moon at nightfall, with the gap growing smaller as the night goes on.
Antares is the 15th-brightest star in the night sky. And astronomers do know quite a bit about it. It’s roughly a dozen times as massive as the Sun, perhaps a thousand times wider, and tens of thousands of times brighter.
The star’s brightness isn’t constant, though. It appears to vary by a few percent. But just how much it varies, and how often, are poorly understood. Estimates for the period of the changes range from about three years to six years. The star may be pulsing in and out like a beating heart. Or bubbles of hot gas bigger than the Sun may occasionally rise to the surface, then sink back into Antares, changing the star’s brightness.
The American Association of Variable Star Observers has been keeping its eyes on Antares since 1945. And it’s been using electronic instruments in that effort since 1981. Even with those decades of observations, though, astronomers still don’t have a good understanding of how and why this massive star changes brightness.
Tomorrow: summertime.
Script by Damond Benningfield

Building the Albert Dock in Liverpool gave a man a powerful thirst. Workers drank up to a dozen pints of beer a day — and that was during the work day, with beer provided by the company. And while the workers drank, beer baron William Lassell got rich.
Lassell used some of that wealth to study the stars. He designed and built one of the world’s largest telescopes, and used it to make many important discoveries.
Lassell was born 225 years ago today. He made his first telescope by age 21. In the 1830s, he built an estate in Liverpool and called it “Starfield.”
At the time, there were few professional astronomers anywhere. Much of the leading research was done by wealthy amateurs like Lassell. In the 1840s, he designed a steam-powered machine to grind the mirror for a 24-inch telescope — one of the largest in the world. The telescope was a trendsetter, because it could track objects across the entire sky.
Using this new instrument, Lassell discovered Triton, the largest moon of Neptune, plus two moons of Uranus and one of Saturn. Later, he moved the telescope to the Mediterranean to escape Liverpool’s rainy, polluted skies. And later still, he built an even bigger telescope.
William Lassell died in 1880. But his contributions remind us of an important era for astronomy — an era made possible by the thirst for knowledge — not to mention the thirst for beer.
Script by Damond Benningfield

Modern astronomy is a job for professionals. Amateurs discover comets and make many other contributions. But most of the cutting-edge research is done by professional scientists using expensive telescopes and other equipment.
In the not-so-distant past, though, many major discoveries were made by “gentleman astronomers” — rich men who built their own telescopes and shared a passion for the stars.
That was especially true in Britain. There wasn’t much public money for telescopes, and only a handful of men made their living as full-time astronomers.
In fact, the Royal Astronomical Society was dominated by amateurs — doctors, lawyers, clergymen, and industrialists who had the time, money, and desire to study the heavens. They built entire observatories — sometimes in England, sometimes in parts of the globe with better climates for skywatching.
In 1845, William Parsons, the Earle of Rosse, built the largest telescope in the world at his estate in Ireland. Its mirror was six feet across, and the 60-foot tube was maneuvered by ropes, pulleys, and cranes. With this behemoth, Parsons drew beautiful sketches of galaxies, and suggested they were “cities of stars” beyond the Milky Way.
And in 1846, beer baron William Lassell discovered Triton, the largest moon of the planet Neptune, with a telescope of his own design. We’ll have more about this “gentleman astronomer” tomorrow.
Script by Damond Benningfield

A pair of cat’s eyes glows just above the north-northwestern horizon as darkness falls. The glowing eyes drop from sight in a hurry. And they’ll drop even lower during the coming nights, before disappearing entirely in the evening twilight.
The “eyes” are the stars Pollux and Castor. They mark the heads of the constellation Gemini. The stars are described as “twins,” but that’s mainly because they’re so close together. Pollux is actually twice as bright as Castor, which is close to its right.
Like all the stars in the night sky, Pollux and Castor rise and set about four minutes earlier each day. They and the other distant stars return to the same point in the sky every 23 hours and 56 minutes. But during that time, Earth moves a little farther in its orbit around the Sun. So Earth has to turn a little bit longer for the Sun to return to the same spot. As a result, the entire background panorama shifts position from night to night.
Gemini is at its best during winter, when it’s in view for all or most of the night. In early spring, it’s in view for about half the night. And now, as spring gives way to summer, only the twins remain in view — but not for much longer. They’ll soon vanish from the evening sky once again. But they’ll return to view a couple of months from now — this time in the dawn twilight — beginning another year-long circle across the night sky.
Tomorrow: “gentlemanly” astronomy.
Script by Damond Benningfield

This might come as a bit of a surprise, but no star is perfectly round. A star’s rotation, and the gravitational tug of any companion stars, can distort the shape. So most stars are slightly flattened. The Sun, for example, is about six miles wider through the equator than through the poles. The Sun’s average diameter is about 865 thousand miles, though, so that slight flattening isn’t noticeable. But some stars are so squashed that they look like lozenges. And still others look like eggs.
Two egg-shaped stars form the system known as Spica, the leading light of the constellation Virgo.
Both of Spica’s stars are much bigger, brighter, and heavier than the Sun. And the stars are quite close together. Their surfaces are just a few million miles apart — so close that we can’t see them as individual stars even through the largest telescopes.
Because the stars are so big, their grip on their outer layers of gas is pretty weak. And at their tight range, the gravity of each star exerts a pretty good pull on the other. That distorts the shapes of both stars — it makes them “bulge” outward. So if we could see the system up close, both stars would look like eggs, with the narrow ends pointing toward each other.
Look for Spica close to the left or lower left of the Moon as darkness falls this evening. The bright star will stand about the same distance to the right of the Moon tomorrow night.
Script by Damond Benningfield