Lots of star clusters adorn the evening skies of summer. That’s because the glowing path of the Milky Way climbs high into the sky. It’s the combined glow of millions of stars that outline the disk of the Milky Way Galaxy. So not only does it contain lots of individual stars, it hosts many star clusters as well.
But a few clusters are far from the path of the Milky Way. One example is Messier 5. It’s in Serpens Caput – the head of the serpent – a region with not much around it.
M5 is a globular cluster – a big ball packed with several hundred thousand stars. Such clusters are scattered all across the sky. Some appear in the disk, but they’re not part of the disk – they loop high above and below it.
Globular clusters are the oldest members of the galaxy. And M5 is one of the oldest – 12 billion years or older. That means its original stars were born when the universe was only about one-tenth of its present age.
Any stars that were more massive than the Sun have burned out. So the remaining original stars are smaller and fainter than the Sun. There’s evidence that a second wave of starbirth rippled through M5 well after the cluster was formed. Some of these stars can still rival the Sun – the “youngsters” of an ancient star cluster.
Messier 5 is high in the south at nightfall. Through binoculars, it looks like a fuzzy star. A small telescope reveals some of the cluster’s individual stars.
Script by Damond Benningfield
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2:19
Moon and Mars
Mars and the Moon stage a spectacular encounter this evening. The Moon will slide just a fraction of a degree from the planet, which looks like a bright star.
Something we’ve learned about both of these worlds is that they have a lot of frozen water. On the Moon, it’s mixed in with the dirt and pebbles, or buried in craters that never see the Sun. On Mars, it’s also mixed in at the surface, but it’s also found in the polar ice caps, in layers of frost, and elsewhere.
On Mars, there’s even evidence of liquid water far below the surface. A study last year said there could be a lot of water buried in spaces in the rocks about 10 miles down – enough water to cover the surface of Mars in an ocean about a mile deep.
And earlier this year, scientists in Japan reported more evidence of that water. They analyzed the observations of the InSight lander, which operated for four years.
The craft listened for “marsquakes.” Sound waves from the quakes traveled through the planet. The new study looked at how different types of waves rippled through the interior. Each type of wave travels differently as it passes through different materials – rock versus water, for example. So comparing the waves revealed the likely presence of water miles below the surface. On Earth, where there’s water, there’s life. So an ocean’s-worth of water could provide a home for life on the Red Planet.
Script by Damond Benningfield
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2:19
Moon and Companions
The crescent Moon and two bright pinpoints stairstep up the western sky this evening. Regulus, the star that represents the heart of the lion, is to the upper left of the Moon. And the planet Mars is about the same distance to the upper left of Regulus. The trio sets in late evening.
The largest feature on the Moon has never been seen directly by human eyes – only by robots. That’s because it’s on the Moon’s far side – the hemisphere that always faces away from us. Only a sliver of its edge can be seen from Earth. And Apollo astronauts saw only a sliver of the opposite edge.
South Pole-Aitken Basin is about 1600 miles wide – one of the largest impact features anywhere in the solar system. It probably formed when a giant asteroid slammed into the Moon soon after the Moon was born.
A Chinese lander, Chang’e 6, touched down in the basin last June. A few weeks later, it brought about four pounds of rocks and dust to Earth. Analysis of some of the samples confirmed that the basin was gouged four and a quarter billion years ago. But the dark volcanic rock that coats much of the basin formed just 2.8 billion years ago, when an ocean of magma cooled and crystallized.
Samples from the near side of the Moon indicate that it was coated with magma at the same time. So the entire lunar surface was covered by an ocean of molten rock – the side we can see, and the side we can’t.
Script by Damond Benningfield
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2:19
Destination Moon
Two decades before astronauts walked on the Moon, American movie-goers got a good preview of what the trip might look like. “Destination Moon” was the first big space movie. And it was the first to accurately explain the science and engineering of a trip to the Moon.
Co-written by science-fiction author Robert Heinlein, the movie premiered 75 years ago today. In the story, millionaire businessmen decide to finance a lunar voyage. They build a nuclear-powered rocket in the desert, then send it on its way. Problems ensue, but the crew lands on the Moon and makes it back home safely.
The backers are convinced in part by a short cartoon that accurately explained how rockets work. In fact, the cartoon was so good that NASA later used a revised version to explain rockets to the public.
Destination Moon also showed the effects of acceleration and zero-gravity. During a spacewalk, one of the crew maneuvered using a tank of oxygen; the first real American spacewalker used a similar technique. And on the Moon, the crew loped along just like the Apollo astronauts.
The film didn’t get everything right. The landscape – painted by space artist Chesley Bonestell – was too sharp and craggy. And the art director added cracks to the surface like those in a dry riverbed to add a feeling of depth.
Still, Destination Moon remains one of the most accurate movies about spaceflight – a fantastic trip to the Moon long before the real thing.
Script by Damond Benningfield
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2:19
Moon and Mercury
Early in its history, the inner solar system was chaotic. Violent collisions might have destroyed many small worlds, while perhaps creating others – including the Moon. It probably formed when a planet as big as Mars rammed into Earth, blasting out debris that came together to make the Moon.
A recent study says that a meteorite discovered a few years ago might be a remnant of one of the demolished worlds.
NWA 15915 was discovered in Algeria. Scientists analyzed the composition, structure, and magnetic properties of the six-pound meteorite. They concluded that it’s a rare type of meteorite – it doesn’t come from any known asteroid, planet, or moon.
But it does have some similarities to Mercury, the smallest planet and the one closest to the Sun. The study suggests that NWA 15915 might have come from a Mercury-like planet born in the same region of the solar system. The planet was demolished long ago by a giant impact. But a few fragments remain.
The findings are preliminary. So it’ll take more work to confirm that a piece of a dead planet fell atop the desert sands of northwestern Africa.
Mercury itself is near the Moon this evening. It looks like a fairly bright star to the left of the Moon. They’re quite low in the sky as twilight fades, so you need a clear horizon to spot them.
Script by Damond Benningfield
USA