StarDate

Family members don’t always stay close together – they can be separated by thousands of miles. But one member of the Milky Way Galaxy’s family takes the separation to extremes. It’s 300,000 light-years from the center of the galaxy – one of the most distant residents of the Milky Way yet seen.

NGC 2419 is a globular cluster – a group of about a million stars. They form a dense ball a few hundred light-years across.

Any star near the middle of the cluster would have thousands of neighbors within a few light-years. Compare that to our own neighborhood – only three stars reside less than five light-years from the Sun.

NGC 2419 is one of the Milky Way’s oldest family members. The cluster was born more than 12 billion years ago – not long after the galaxy itself. All of its big, bright stars burned out long ago. So almost all of the remaining stars are much less massive than the Sun.

The cluster follows a highly stretched-out orbit around the center of the Milky Way. That’s led to suggestions that it was born elsewhere, then captured by the Milky Way. But there’s no confirmation of that idea. So NGC 2419 is still considered a far-away relative of the rest of the Milky Way.

The cluster is in the uber-faint constellation Lynx, which is in the east-northeast at nightfall. NGC 2419 is an easy target for just about any telescope.

Script by Damond Benningfield

Alpha Lyncis is only about a third of the age of the Sun. Yet the star has already zoomed through the prime phase of life. Now, it’s nearing the end of its life. And it’s letting us know about it – it’s the brightest star of the constellation Lynx.

That’s not necessarily saying much. Lynx is a large constellation, but it’s faint – only a few of its stars are bright enough to see from light-polluted cities or suburbs. In fact, the astronomer who created it, in the 1600s, called it “Lynx” because you needed the eyes of one to see it.

Alpha Lyncis is classified as a red giant. It’s about half-again the mass of the Sun. Heavier stars age more quickly. Such a star “burns” through the original hydrogen in its core in a hurry. As the core adjusts to the change, the star’s outer layers puff up. Today, Alpha Lyncis is more than 50 times the diameter of the Sun. As it got bigger, the star got cooler and redder – making it a red giant.

Puffing up also made the star hundreds of times brighter than the Sun. So Alpha Lyncis is visible – faintly – even though it’s a little more than 200 light-years away. That makes it one of the few stars in this faint constellation that you don’t need the eyes of a lynx to see.

Lynx is well up in the east-northeast at nightfall. It’s about half way between the Big Dipper and the twins of Gemini. But you need nice, dark skies to see much.

More about the constellation tomorrow.

Script by Damond Benningfield

The Moon snuggles close to the bright star Spica late tonight. They climb into good view by about midnight, and are high in the sky at dawn. At their closest, they’ll be separated by just a couple of degrees – about the width of your finger held at arm’s length.

That closeness is just an illusion – the Moon and the star are separated by a vast gulf.

The Moon is our closest neighbor. Tonight, it’s a little less than a quarter of a million miles away. At that distance, sunlight reflecting from the lunar surface takes about one and a third seconds to reach Earth. That means we see the Moon as it looked one and a third seconds earlier.

The Moon is moving farther from us – by an inch and a half per year. That’s a result of the tides. Earth and Moon exert a gravitational grip on each other. That slows Earth’s rotation, making the days a little longer. To balance the books, the Moon moves farther away.

Spica is more than nine billion times farther than the Moon. Its light takes about 250 years to reach Earth – the star is 250 light-years away. So as you look at Spica tonight, you’re actually seeing the bright star as it looked 250 years ago – about the time of the American Revolution.

And it’s moving away as well – by about 60 million miles per year. That’s a result of Spica’s motion around the center of the galaxy – an orbit that’s carrying the brightest star of Virgo into the distance.

Script by Damond Benningfield

The star cluster M79 is messy. It’s shedding some of its stars, creating a “tail.” Over the eons, in fact, the cluster might have lost most of the stars it was born with.

Messier 79 is a globular cluster – a ball-shaped family of about 150,000 stars. The cluster is more than 11 billion years old, so its stars are among the oldest in the entire Milky Way Galaxy.

There’s a trail of stars behind the cluster. The stars probably were stripped away by the gravity of the rest of the galaxy – especially its dense core.

Today, M79 is about 42,000 light-years from the Milky Way’s heart. But its orbit might bring it within just a few hundred light-years of the center. At that distance, the gravity of the galaxy’s core overpowers the gravity of the cluster. So stars in M79’s outskirts are pulled away. Eventually, they move away, and follow their own paths across the galaxy.

Some simulations have suggested that M79 has lost up to 85 percent of its original population of a million stars or so. And every future passage through the heart of the galaxy will pull away more stars – leaving only a glimmer of M79’s original glory.

M79 is in Lepus, the hare. The constellation is close to the lower right of bright Orion, in the southeast at nightfall. M79 is below the outline of the rabbit. You need binoculars to pick it out.

Script by Damond Benningfield

In 1845, British astronomer J.R. Hind saw an amazing star in the constellation Lepus, the rabbit. He wrote that the star looked “like a drop of blood on a black field.” Officially, the star is called R Leporis. But it’s also known as Hind’s Crimson Star – a star that looks redder than almost any other star in the galaxy.

R Leporis is a little heavier than the Sun. But it’s much later in life, which makes it a lot more interesting. It’s “fused” the original fuel in its core to make oxygen and carbon. Today, it’s producing energy in shells of hydrogen and helium around the core.

Those changes have caused the star’s outer layers to puff up, so R Leporis is hundreds of times the Sun’s diameter. But those layers are unstable. They pulse in and out like a beating heart. Each “beat” lasts about 14 and a half months. During that cycle, the star’s brightness varies dramatically; at its peak, it’s hundreds of times brighter than at its faintest.

As the star pulses, its temperature changes. At its largest, it’s a bit cooler, so it looks redder. And that color is amped up by the material in its outer layers. Carbon is pulled up from deep inside the star. It absorbs blue wavelengths of light, allowing the red to shine through – enhancing the “bloody” look of Hind’s Crimson Star.

Lepus is in the southeast in early evening, to the lower right of Orion. But you need a telescope to see Hind’s Crimson Star.

Script by Damond Benningfield