StarDate

An astronomer greets visitors to a science museum in Canberra, Australia. He’s made of riveted iron plates, and he stands atop a wide ring, gazing skyward through a smaller ring in his right hand. He’s the last remnant of an historic telescope that was destroyed in a massive wildfire.

The fire blazed across Australia in January of 2003. It destroyed most of Mount Stromlo Observatory, one of the major astronomy research centers in the southern hemisphere. The fire consumed five telescopes, plus a laboratory where scientists and engineers built astronomical instruments.

One of the casualties was the Yale-Columbia Telescope. It was a 26-inch refractor – a type of telescope that uses lenses to gather and focus starlight. It was built in 1924, and had been operating at Mount Stromlo for half a century. Astronomers had used it to measure the distances to stars, to study double stars, and more.

After the fire, an Australian science institute commissioned a sculptor, Tim Wetherell, to create an artwork from the telescope’s remains. The result was “The Astronomer” – the piece on display in Canberra.

The figure stands on a setting circle – a wide ring that indicated where the telescope was pointing. It has numbers at 10-degree intervals, from zero to 180. The astronomer is holding a smaller version of the ring in his hand – continuing to look at the stars long after the telescope’s demise.

Script by Damond Benningfield

The crescent Moon and the planet Venus team up in the evening twilight tonight. Venus is the brilliant “evening star.” It’s below the Moon, and it sets by the time the sky gets fully dark.

Venus is enveloped by an unbroken layer of clouds – one of the reasons the planet looks so bright. The clouds are a few dozen miles above the surface. And they’re speedy – they race around the planet at up to 335 miles per hour – twice as fast as the winds in a category-5 hurricane. They make a full turn around Venus every four days. That’s more than 50 times faster than the planet is turning on its axis.

That high-speed motion is called super-rotation. No one knows for sure what causes it. A study a few years ago said it might be powered by the Sun. The clouds are hottest at the equator, where the sunlight is strongest. The hotter atmosphere flows outward, toward the poles and toward the nightside – reaching super-fast speeds.

Super-rotation doesn’t extend all the way to the surface, though. Below the clouds, the wind speed drops dramatically. At the surface, there’s almost no wind at all. But the atmosphere is quite dense – more than 90 times the density of Earth’s atmosphere. Any wind at all exerts a lot of pressure, so it can erode the surface. That can wear away mountains, and gouge channels that look like they were carved by flowing water – all below the speedy clouds of the planet Venus.

Script by Damond Benningfield

Spring arrives in the northern hemisphere tomorrow morning, when the Sun crosses the celestial equator from south to north – the vernal equinox. Over the next three months, the Sun will travel ever farther northward, bringing longer, warmer days north of the equator.

Vernal comes from the Latin word for spring. And equinox means “equal nights.” Theoretically, all points on Earth should see equal amounts of daylight and darkness on the equinox. But for several reasons, the interval between sunrise and sunset – which should be exactly 12 hours – varies by a few minutes.

The vernal equinox marks the starting point for the system that astronomers use to plot the sky.

They measure the positions of astronomical objects using coordinates called right ascension and declination – the equivalent of longitude and latitude. Right ascension is measured in hours. The point where the Sun crosses the celestial equator – the projection of Earth’s equator on the sky – on the vernal equinox is designated as zero hours. It’s the equivalent of zero degrees longitude – the line that runs through Greenwich, England.

And just as Earth’s equator marks zero degrees latitude, the celestial equator is designated zero degrees declination. So at the moment of the vernal equinox, the Sun stands at celestial coordinates zero-zero – beginning a new cycle through the stars.

Tomorrow: the Moon and a bright companion.

Script by Damond Benningfield

The heart of the galaxy Messier 87 is a cosmic maelstrom. A disk of super-heated gas that’s hundreds of times the size of our solar system encircles a monster black hole. Gas at the inner edge of the disk spirals into the black hole, producing huge amounts of X-rays. Enormous magnetic fields channel some of the gas into powerful “jets.” It’s not a place you’d ever want to visit. But it’s a fascinating region to study from far away.

M87 is a giant elliptical galaxy. It looks like a fat, fuzzy rugby ball. It’s bigger than our home galaxy, the Milky Way. It has many more stars, and could be up to 200 times as massive as the Milky Way.

The black hole at its heart is impressive, too. It’s roughly 1400 times the mass of the black hole at the center of the Milky Way. It’s pulling in gas, dust, and other debris. That material forms a disk that’s hundreds of times wider than the orbit of Neptune, the Sun’s most-distant planet.

A recent study found that material in the disk is falling into the black hole at a quarter of the speed of light. And the black hole itself is rotating at 80 percent of lightspeed or faster. That rotation generates a powerful magnetic field. The field catches some of the infalling material and shoots it back into space. That creates a “jet” of charged particles that’s thousands of light-years long – a beam of deadly radiation from the heart of Messier 87.

Script by Damond Benningfield

A galaxy cluster is like a cosmic blender. It stirs up the galaxies and the space between them. Nothing is left undisturbed.

A perfect example is the Virgo Cluster. It consists of more than 1500 individual galaxies, centered about 55 million light-years away. Most of them are fairly small and faint. But a few are monsters – many times the size and mass of our home galaxy, the Milky Way.

The cluster’s galaxies are packed fairly close together. So the gravity of each galaxy pulls at its neighbors. That distorts the shape of some of the neighbors, making them lopsided. It also causes big clouds of gas to collapse and give birth to new stars. And it pulls many stars out of the galaxies, into the space between them. In fact, up to one-tenth of the stars in the cluster may be roaming through intergalactic space.

The cluster’s brightest galaxy is Messier 49. It was the first to be discovered, in 1771. It’s a giant elliptical, so it looks like a fat, fuzzy rugby ball. It’s much bigger than the Milky Way, and many times its mass. And a supermassive black hole inhabits its heart.

The biggest and heaviest member of the cluster is Messier 87, and we’ll talk about it tomorrow.

The Virgo Cluster is centered along the border between Virgo and Leo. That spot is low in the east at nightfall and climbs high across the sky later on. Many of the galaxies are easy targets for small telescopes.

Script by Damond Benningfield