If you ever want to chat with someone on another planet, you better have a lot of patience. It takes a long time for a message from Earth to reach another world, and just as long for the reply to reach Earth.
That’s because radio waves travel at the speed of light. And although light is pretty swift, its speed is limited – 670 million miles per hour. Given the scale of the solar system, that means there’s a long pause between halves of a conversation.
Consider the planets that flank the Moon at dawn tomorrow: brilliant Venus to the lower left of the Moon, and fainter Saturn to the upper right.
Right now, Venus is more than 58 million miles away. At that distance, it would take a radio signal from Earth about five and a quarter minutes to get there – a round-trip time of 10 and a half minutes.
Saturn is about 930 million miles away. So the round-trip travel time is about two hours and 45 minutes.
That’s a big concern for the folks who send probes to these and other planets. Despite what you might see in sci-fi movies and TV shows, there’s no way to have a real-time conversation. So spacecraft are programmed to do much of their work without direct help from Earth. And if they encounter a problem, they shut down most of their systems and place a call for help – then settle in for the long wait to hear from home.
More about the Moon and Venus tomorrow.
Script by Damond Benningfield
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2:19
Moon and Saturn
A 900-mile-wide, two-toned walnut orbits the planet Saturn. It’s Saturn’s third-largest moon, and definitely the most eye-catching. One hemisphere is as dark as coal, while the other is as bright as sea ice. And a mountain ridge wraps around the equator, making it look like a walnut.
Iapetus was discovered in 1671. And right away, astronomers realized there was something odd about it. It was easy to see when it was on one side of Saturn, but invisible on the other. Today, we know why that’s the case: the planet’s leading hemisphere is 10 to 20 times brighter than the trailing hemisphere.
The leading idea says that long ago, the darker side was pelted by dust and rocks blasted off some smaller moons. The darker material trapped the Sun’s heat, vaporizing ices. The vapor drifted to the other side, where it froze, making that side bright. And that process continues today – making Iapetus the “yin and yang” of moons.
The ridge around the equator is about six miles high. It might have formed long ago when Iapetus rotated much faster than it does today. Or it might be the remains of a ring that collapsed onto the surface – making Iapetus look like a walnut.
Saturn appears quite close to our own Moon at dawn tomorrow. It looks like a bright star to the lower left of the Moon. The much-brighter planet Venus is farther to the lower left. More about this morning lineup tomorrow.
Script by Damond Benningfield
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2:19
Padding the Middle
For the most part, black holes come in two varieties: small and jumbo. The small ones are the remnants of dead stars. They range from a few to about a hundred times the mass of the Sun. The jumbos inhabit the hearts of galaxies. They range from about a hundred thousand to several billion times the Sun’s mass. But there just isn’t much in the middle.
In fact, astronomers have logged only a few dozen medium-sized black holes. And many of those are controversial – they’re hard to confirm. Most of them are in other galaxies, so it’s hard to see their influence on the stars and gas around them.
One recent study may have added to the tally. Using observations designed to study dark energy, scientists said they discovered about 300 medium-sized black holes. About 70 of them inhabit the centers of small galaxies. Those black holes are gobbling gas and dust around them, making them brighter and easier to find.
Theory says there should be many more black holes in size “medium.” They may be the remnants of the ultra-massive stars that populated the early universe. Or they may have formed when dense clumps of gas collapsed under their own gravity. Either way, it’s possible that such black holes were the “seeds” from which the jumbo black holes grew.
For now, the search continues for these hard-to-find medium-sized black holes.
Script by Damond Benningfield
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2:19
Omega Centauri
The closest galaxy we can see other than our own Milky Way may be inside the Milky Way. Its outer precincts have been stripped away, leaving only its core – a tight ball of 10 million stars. And a rare type of black hole appears to lurk in its middle.
Omega Centauri rolls low across the south during the night. The view is better from the southern half of the country. To the eye alone, it looks like a fuzzy star.
Omega Centauri is classified as a globular cluster – a family of very old stars. It’s the biggest one in the galaxy. But it probably wasn’t born in the Milky Way. Instead, it began as a separate galaxy. But it was reeled in by the Milky Way’s gravity, which also pulled away most of its stars. Only the stars in the galaxy’s core stuck together.
An intermediate-mass black hole appears to inhabit the center of the cluster. Such beasties are rare. Most black holes are either no more than about a hundred times the mass of the Sun, or a few hundred thousand times the Sun’s mass or more.
A study a couple of decades ago reported a possible black hole in Omega Centauri weighing 40,000 times the Sun’s mass. Later work suggested that number was too high. The most recent estimate was compiled from 20 years of observations by Hubble Space Telescope. It puts the black hole at about 8,000 times the Sun’s mass – a rare black hole in the remnant of a dead galaxy.
More about mid-sized black holes tomorrow.
Script by Damond Benningfield
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2:19
Kornephoros
Mighty Hercules stands well up in the east and northeast as night falls. His most prominent feature is the Keystone, a lopsided square of stars that represents his body. But the constellation’s brightest star isn’t part of the Keystone. Instead, it represents the entire strongman: Its name, Kornephoros, comes from a Greek word that means “the club bearer” – Hercules himself.
Like many of the stars in the galaxy, there’s more to Kornephoros than meets the eye: It consists of two stars, not one. One star is smaller and fainter than the Sun, so it’s not visible to the eye alone.
The visible star, on the other hand, is about three times the mass of the Sun, almost 20 times the Sun’s diameter, and 150 times its brightness. So the star is an easy target even though it’s about 140 light-years away.
The star is nearing the end of its life. It’s probably consumed the hydrogen fuel in its core, converting it to helium. That’s caused the core to get smaller and hotter. The extra radiation pushes on its outer layers, causing them to puff up to giant proportions.
Today, Kornephoros is fusing the helium to make carbon and oxygen. Eventually, that process will end. The star will lose its outer layers, leaving only its dead core – and the “club bearer” will vanish from sight.
For now, though, look for it due east at nightfall, halfway up the sky – the first modestly bright star to the right of the Keystone.
Script by Damond Benningfield
USA