StarDate

Fifteen 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 on its way on April 11th., 2001

The craft was named 2001 Mars Odyssey — a tribute to Arthur C. Clarke, author of “2001: A Space Odyssey.” And like most of Clarke’s books, Mars Odyssey was a big success. It entered orbit around Mars on October 23rd. And 15 years later, it’s still going. It’s the longest-operating spacecraft not only at Mars, but 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 evidence of where liquid water once pooled on the surface. And it found the first caves ever seen on Mars — possible places for future missions to look for microscopic life.

Odyssey has also served as a relay station for several Mars landers and rovers.

And its mission isn’t over. Even though it’s had some system failures, it has enough fuel to keep going for a while. So barring any unexpected problems, Mars Odyssey could add several more years to its record-breaking reconnaissance of the Red Planet.

Script by Damond Benningfield

Astronomical distances can be mind boggling. Our closest neighbor, the Moon, is a quarter of a million miles away — equal to about 10 trips around Earth’s equator. The closest planet, Venus, is always at least a hundred times farther. And the closest neighboring star system, Alpha Centauri, is about a million times farther still.

Yet even that enormous gulf is nothing more than a hop away compared to the most distant object that’s easily visible to the unaided eye. The Andromeda galaxy is more than half a million times farther than Alpha Centauri — two-and-a-half million light-years.

Right now, Andromeda stands about half-way up the eastern sky as night falls. To the eye alone, it looks like a faint patch of light about the width of the Moon. Binoculars bring it into better view.

Like our home galaxy, the Milky Way, Andromeda is a wide, flat disk. The visible part of the disk spans more than a hundred thousand light-years. But powerful telescopes show that stars taper off into space well beyond that, making the disk twice as wide as the Milky Way’s.

We see the galaxy almost edge-on, which raises another mind-boggling detail about astronomical distances. It takes the light from the far edge of the disk longer to reach our eyes than the light from the near edge of the disk. So there’s no way to see the galaxy at a single point in time. Instead, we see different parts of it as they looked over a span of almost a hundred thousand years.

Script by Damond Benningfield

Andromeda is a pretty big constellation — it rates 19th out of 88. It’s also ancient — it was first drawn several thousand years ago. And it’s fairly famous, too — its namesake was featured in plays by the ancient Greeks, and in more recent times in movies and TV shows.

Yet it’s a bit disappointing to look at. Andromeda’s main figure is two streamers of stars that form a long, skinny V. But it’s not an attention grabber — it takes some patience to find it. Right now, it’s in the east and northeast at nightfall, and passes high overhead by midnight.

The constellation represents a princess from the mythical land of Ethiopia.

The princess was chained at the shore as a sacrifice to a sea monster. The monster was sent to punish the country after Andromeda’s mother, Cassiopeia, boasted that she was more beautiful than the sea nymphs. But the young maiden was rescued at the last moment by Perseus, and the gods placed all of them in the stars.

Andromeda’s brightest star, Alpha Andromeda, forms the top of the V. Beta Andromeda, which is only slightly fainter, stands to its lower left during the early evening hours.

The constellation’s real stars, though, are its galaxies. Three of them are easy targets for small telescopes, and one is visible to the unaided eye. In fact, it’s the farthest object you can see without any optical aid: M31, which is two-and-a-half million light-years away. We’ll have more about M31 tomorrow.

Script by Damond Benningfield

One of the most colorful star systems around climbs high across the sky on autumn nights. A telescope reveals two stars — one that looks yellow-orange, and another that looks blue.

Almach is one of the brightest stars of the constellation Andromeda, the princess. It’s about half-way up the northeastern sky as night falls, and passes high overhead in the wee hours of the morning.

The system is about 350 light-years away. At that great distance, the eye alone sees only a single pinpoint of light. It takes a telescope to reveal Almach’s double identity.

The orange star is nearing the end of its life, so it’s going through a series of big changes. Its core has gotten smaller and hotter, so its radiation pushes more strongly at the surrounding layers of gas. That’s caused the star to puff up to giant proportions — it’s several dozen times wider than the Sun. And that expansion has caused the star’s surface to get cooler, which is why it looks yellow-orange.

The blue star actually consists of three stars. One is visible through a small telescope, a second comes into focus with a bigger telescope, and the third reveals its presence only to special instruments.

All three stars are bigger and more massive than the Sun. They’re also hotter, so their surfaces are white with a hint of blue. Seen next to their orangey companion, their combined light looks even bluer than it really is — making Almach one of the most beautiful double stars in the galaxy.

Script by Damond Benningfield

Halley’s Comet won’t return to the inner solar system for almost half a century. But it makes its presence known at this time of year with a meteor shower. The shower isn’t named for the comet, though, but for the region of the sky in which the meteors appear to “rain” into the atmosphere — the constellation Orion.

A meteor shower takes place when Earth flies through the path of a comet, which is a big ball of frozen water and gases mixed with bits of rock and dirt. As the comet gets close to the Sun, some of the ices vaporize, releasing some of the solid particles. Over time, these bits of dust spread out along the comet’s path.

Halley has made a lot of trips around the Sun, so it’s shed a lot of debris, which has spread out all along its orbit. Earth flies through this path every October. As the particles of comet dust hit the atmosphere they vaporize, forming the glowing streaks known as meteors.

The Orionids are pretty reliable, although not usually spectacular. At their peak, they produce a couple of dozen meteors per hour.

This year’s shower should be at its best late tonight. Unfortunately, the Moon rises around midnight, so it’ll cast its glow in the sky during the shower’s peak. And the Moon will be quite close to Orion, making things even worse.

The best chance to see the meteors is to get away from city lights, and hope for some bright ones to puncture the sky — some bright “calling cards” of Halley’s Comet.

Script by Damond Benningfield

A massive star in a nearby galaxy is on the run. It’s moving faster than any other known star — fast enough to escape its home galaxy.

The star is a member of M31, the Andromeda galaxy. Under dark skies, the galaxy is visible to the unaided eye as a hazy smudge of light. Right now, it’s about half-way up the eastern sky as night falls. At a distance of two-and-a-half million light-years, it’s the farthest object that’s easily visible to the eye alone.

Astronomers discovered the runaway while looking for red supergiants in M31. These stars are much bigger, heavier, and brighter than the Sun. They’re also nearing the ends of their lives, which is one reason they’re so puffed up.

One of the supergiants is moving in our direction far faster than any other star in the survey. The astronomers estimated that its overall speed relative to the rest of M31 is about 650,000 miles per hour.

The star probably was born with a cluster of other massive stars. Gravitational interactions among the stars may have kicked this one out of the cluster. The kick was so powerful that the star may be moving fast enough to escape from M31.

Or it would escape if it lived long enough. The star is expected to explode as a supernova in the next million years or so — long before it can escape the galaxy. But the blast probably will leave a dead, heavy core. It will continue to race away from M31 — and may eventually escape into intergalactic space.

Script by Damond Benningfield

The Moon has been playing a game of celestial hide-and-seek all year long. Almost every month, it’s passed directly in front of Aldebaran, blocking the bright eye of Taurus the bull from view. And it will do so again tonight. The disappearing act, known as an occultation, will be visible across a wide swath of the United States.

The Moon’s orbital path is such that the Moon passes close to Aldebaran every month. But that path carries the Moon north and south of Aldebaran’s position in the sky. The path overlaps Aldebaran during cycles that last about four years. The current cycle began in January of last year, and continues through September of 2018. After that, we won’t see another occultation of Aldebaran for another 15 years.

Tonight’s occultation will be visible to the south and east of a line that runs from about Los Angeles to Minneapolis and on through the middle of Lake Superior.

The exact timing depends on your location. From Baltimore, for example, the occultation begins when Aldebaran disappears behind the Moon at about 1:38 a.m., and lasts for more than an hour. From Chicago, it starts at 12:38 a.m., and lasts for about 44 minutes. And from San Antonio, it starts a little after midnight and continues for an hour.

The view is especially beautiful before and after the occultation, as bright Aldebaran snuggles quite close to the Moon — an act that’ll be repeated many times over the next couple of years.

Script by Damond Benningfield

In four years, the European Space Agency plans to send a rover to Mars. It’ll be the agency’s most ambitious planetary mission yet; the rover will drill into the Martian surface to hunt for signs of life.

The mission team hopes to get in a rehearsal for the rover’s landing this week. A probe is scheduled to land on Mars on Wednesday. It has limited battery power, so it’ll last for only a couple of days. But it’ll provide experience at landing on Mars, and check out some of the equipment for the rover mission.

The probe is half of a larger mission called ExoMars. It was launched by a Russian rocket earlier this year.

The other half of the mission is known as Trace Gas Orbiter. It’ll enter orbit on Wednesday, then spend the next 14 months lowering its altitude before beginning its observations.

Its mission is to sniff the upper atmosphere for gases that are related to life, especially methane.

Most of the methane in Earth’s atmosphere comes from living organisms. And traces of methane have been detected in the atmosphere of Mars. That suggests that microscopic organisms could be living below the Martian surface.

But the methane could also be produced by geologic processes instead of life. The instruments aboard Trace Gas Orbiter are designed to determine which is the case — perhaps telling us whether the future rover is likely to find signs of life below the Martian surface.

Script by Damond Benningfield

A European probe to Mars is scheduled to arrive on Wednesday. One part of the ExoMars mission, called Schiaparelli, will land on the Red Planet. The other, known as Trace Gas Orbiter, will study the Martian atmosphere from orbit.

The lander will operate for only a couple of days. Although it’ll make some scientific observations, its main goal is to pave the way for a Mars rover in a couple of years. It will allow European engineers and scientists to gain experience at landing on Mars.

To help make that landing as precise as possible, navigators here on Earth are getting help from quasars. These cosmic beacons are brilliant disks of hot gas around supermassive black holes in distant galaxies.

Navigators use more than one tracking station here on Earth to triangulate the craft’s position. But Earth’s atmosphere can alter its radio waves. So the tracking stations also monitor one or more quasars at the same time.

The radio characteristics of the quasars are well known. Any change in the quasar signal tells engineers what’s happening to radio waves in the atmosphere. That allows them to correct signals from ExoMars. Engineers say that’ll make it possible to pinpoint the craft’s position to within about a half mile — making it easier to hit the bullseye on Mars.

We’ll have more about ExoMars tomorrow. In the meantime, look for the planet low in the south as night falls. It looks like a bright orange star, to the left of teapot-shaped Sagittarius.

Script by Damond Benningfield

It’s pretty easy to hunt up the Moon tonight. It’s full, so it rises around sunset and is in view all night long. And as the first full Moon after the Harvest Moon, it’s known as the Hunter’s Moon.

In today’s world, that name doesn’t mean a whole lot. On average, the Hunter’s Moon isn’t any brighter or closer to Earth than any other full Moon.

In centuries gone by, though, the Hunter’s Moon was an important marker in the calendars of many cultures. The moonlight illuminated the now-barren fields, making it easier for hunters to track their quarry and stock up for the winter. And thanks to the time of year, from high northern latitudes the Moon rises a bit earlier on the nights around the Hunter’s Moon than the average full Moon, providing even more light.

Over the course of a full year, the Moon rises about 50 minutes earlier each night. But based on the time of year and the viewer’s latitude, the exact difference on any given pair of nights varies dramatically — from just a few minutes to more than an hour.

In autumn, the angle of the Moon’s path across the sky is such that the gap between moonrises around the full Moon is shorter than average. But it’s just the opposite around new Moon. Then, the gap is around an hour or even longer. That means you have to wait longer to see the thin crescent Moon pop into view in the evening sky.

So enjoy the Hunter’s Moon, shedding its light on the autumn landscape.

Tomorrow: guiding lights for a mission to Mars.

Script by Damond Benningfield