StarDate

In Gulliver’s Travels, which was published 300 years ago today, Jonathan Swift wrote that the people of Laputa had made an important discovery: “two lesser stars, or satellites, which revolve about Mars.” The fictional moons were small and close to the surface, orbiting the Red Planet in a matter of hours.

Earthly astronomers took a little longer to find the real moons – they weren’t discovered until 1877. They were named Phobos and Deimos – fear and panic – after attendants of the god of war.

Phobos is the larger moon. It’s lumpy, with an average diameter of about 14 miles. It orbits just 3700 miles from the surface of Mars. It rises in the west, then sets in the east less than four-and-a-half hours later.

Deimos is about eight miles in diameter. It’s about three times farther from Mars, so it takes about two-and-a-half days to cross the sky, from east to west. It’s shaped a bit like a potato with a big dimple on one side.

Several spacecraft have flown past the moons. But they’ve raised a lot of questions about them. Now, 300 years after Gulliver’s Travels, scientists may take a big step toward finding some answers. Japan launched the Mars Moons Exploration mission this month. The craft will study both moons from close range. And it will touch down on Phobos, hoovering up a few grams of pebbles and dust for return to Earth.

More about that tomorrow.

Script by Damond Benningfield

The Moon is crossing the constellation Taurus. Tonight, it’s quite close to the bull’s shoulder – the Pleiades star cluster. The bull’s bright eye, the star Aldebaran, is well below the Moon as they climb into view. It’ll be about the same distance to the right of the Moon tomorrow night.

A dead “starship” is headed in Aldebaran’s direction. It won’t get there for more than two million years. But just in case anyone finds it, it carries a message.

Pioneer 10 was launched in 1972. It was the first spacecraft to fly through the asteroid belt, and the first to explore Jupiter, the Sun’s largest planet. After that, it raced out of the solar system and into interstellar space. NASA last heard from it in early 2003. Today, it’s more than 13 billion miles away.

The “message” is a plaque that’s made of aluminum and coated with gold. It measures nine by six inches. It includes the outlines of a naked man and woman. They’re standing in front of an outline of Pioneer to indicate their size. It also includes a chart of the solar system that shows Pioneer’s home planet. Other diagrams help pinpoint Earth’s location in the galaxy.

No one expects Pioneer to ever be found. It won’t get all that close to Aldebaran, and the star’s only known planet isn’t a good home for life. After Aldebaran, Pioneer 10 will continue sailing through the cosmos – an extinct emissary from Planet Earth.

Script by Damond Benningfield

If you overlook the fact that you’d be instantly vaporized, there’d be one small advantage to standing at the surface of the Sun: You’d age more slowly than your friends and family back on Earth.

The effect is called time dilation. It comes from Relativity – Albert Einstein’s theories of motion and gravity. They tell us that clocks at different locations tick at different rates. Keep in mind, though, that they tick at different rates as seen by observers moving at different speeds and in different gravitational fields.

According to Special Relativity, as you go faster your clock slows down. General Relativity says your clock slows down as the pull of gravity gets stronger.

On Earth, the effect has been confirmed by placing atomic clocks in high-flying jet aircraft. And GPS satellites are programmed to compensate for the effect. If they weren’t, the whole system would fail within days.

Time dilation is more pronounced at the surface of the Sun because of the Sun’s great mass. A clock there would slow down by about 67 seconds per year compared to one on Earth. And when the Sun expires, its “corpse” will have even stronger gravity, slowing a clock by more than an hour per year.

Time dilation is strongest just outside a black hole. An outside observer would see a clock at the cusp move almost infinitely slowly – never ticking off the final second before plunging into the black hole.

Script by Damond Benningfield

Few of us have to hunt wild game to survive the long, cold winter these days. But that hasn’t always been the case. Native tribes and European settlers alike had to stock up as the weather grew cooler. And they relied on an autumn full Moon for help: the Hunter’s Moon.

And that Moon is coming up tonight. It’s the full Moon after the Harvest Moon, which appeared in September.

Like the Harvest Moon, the Hunter’s Moon helped people prepare for winter. Its light made it easier to see deer and other animals. And at high northern latitudes, the Moon rises only about a half-hour later each night around full Moon – a much smaller gap than average. So the big, bright Moon was in view by the time evening twilight faded – allowing hunters to stay in the fields long into the night.

Despite what you might think, the Harvest and Hunter’s Moons aren’t any bigger and brighter than any other full Moons. The Moon’s orbit and its cycle of phases aren’t synchronized. So some years the Hunter’s Moon is closer than average. But in other years, it’s farther than average. This year we’re in luck, because it’s on the closer side. At the moment of full Moon, it’ll be about 230,000 miles away – a few thousand miles closer than average.

That helps make this year’s Hunter’s Moon an especially beautiful sight, lighting the autumn fields for hunters – and everyone else, too.

Tomorrow: stretching the year.

Script by Damond Benningfield

Twenty-five years ago, NASA needed a hit. Its previous two missions to Mars had failed – both of them as they were arriving at the Red Planet. So it prepared the next mission with extra care, and sent it on its way on April 7th, 2001.

The craft was named 2001 Mars Odyssey – a tribute to Arthur C. Clarke, the author of “2001: A Space Odyssey.” And like most of Clarke’s books, Mars Odyssey was a big hit. It entered orbit around Mars on October 23rd – 25 years ago this week. It’s the longest-operating spacecraft at any body in the solar system other than Earth.

Among its many accomplishments, Odyssey has mapped the chemical and mineral composition of the entire Martian surface. It also discovered evidence of vast amounts of ice just below the surface. And it found places where liquid water once pooled on the surface. Those observations helped scientists pick interesting locations for landers and rovers. And it found the first caves ever seen on Mars – possible places for future missions to look for microscopic life.

Odyssey also has served as a relay station for Mars landers and rovers. And it recorded radiation levels at the planet – critical information for planning human missions.

As of late summer, the craft was still going. And barring any unexpected problems, it could add several more years to its record-breaking odyssey at the Red Planet.

Script by Damond Benningfield