StarDate

Time is tricky. There’s no “universal” clock ticking along at a constant rate. Instead, every clock in the universe ticks at its own rate, influenced by its motion and by the gravity of the matter around it. Those influences are built into the clocks of GPS satellites; without them, the system would fail within days.

Scientists recently calculated how clocks would tick on Mars – an average of 477 millionths of a second faster per day than clocks on Earth. But as Mars orbits the Sun, that rate varies by up to 226 millionths of a second.

The scientists used Albert Einstein’s theories of gravity and motion. Stronger gravity and faster motion both make a clock move more slowly as seen by an outside observer. The surface gravity of Mars is only about a third as strong as Earth’s. And because the planet is farther from the Sun, it orbits the Sun more slowly.

But Mars’s orbit is more lopsided than Earth’s, so its orbital speed varies more dramatically. The changing distance also alters the gravitational influence of the Sun, as well as that of Earth and the Moon. The researchers incorporated all of these variables – and many others – to figure out the ticking of Martian clocks.

Mars is working its way into the morning sky. It’s quite low in the east during dawn twilight. But the planet will climb a little higher day by day, and will be in good view this summer.

More about Mars tomorrow.

Script by Damond Benningfield

The Moon creeps up on the heart of Leo tonight, the star Regulus. Regulus is close to the upper left of the Moon at nightfall. The Moon will move closer before they set, around 2 a.m. They’ll be closest together as seen from the West Coast.

The star we see as Regulus is called Regulus A. It’s several times bigger and heavier than the Sun, and much brighter. A tiny companion star is so close that it’s impossible to see through the glare.

That duo appears to have two more companions, Regulus B and C. They form their own pair, orbiting each other once every 600 years or so. Regulus B is about 80 percent the size and mass of the Sun, and one-third as bright. Regulus C is a third of the Sun’s mass and size, and just two percent as bright.

Regulus B and C are 79 light-years from Earth – the same distance as Regulus A. And they’re moving through space in the same speed and direction as the brighter star. That suggests that they’re bound to Regulus A. But they’re a long way from it – several thousand times the distance between Earth and the Sun.

So astronomers haven’t watched the system nearly long enough to calculate a mutual orbit for the two pairs of stars. Estimates say it would take more than a hundred-thousand years for them to complete one circuit. So it’s possible that they’re not really bound at all – just a chance alignment at the bright heart of the lion.

Script by Damond Benningfield

A space telescope is scheduled for a rescue. If the plan works, a small spacecraft will boost it to a higher orbit. That would allow the telescope to keep watching the skies for years.

Neil Gehrels Swift Observatory was launched in late 2004. It watches the universe at a wide range of wavelengths, from visible light to gamma rays – the most powerful form of energy.

Its original mission was to study gamma-ray bursts – the explosive deaths of massive stars. They’re among the most violent events in the universe, and among the “swiftest” – they fade in as little as a few seconds. So the telescope has to pivot swiftly when a new burst occurs – hence its name.

Swift’s original altitude was 375 miles. But the Sun has been especially active in recent years. It’s heated Earth’s atmosphere, causing it to expand. That’s dragged the telescope to less than 250 miles. There’s a good chance it could fall from orbit by the end of the year.

The rescue mission is scheduled for launch within a few weeks. Swift wasn’t designed to be serviced in orbit, so it’ll take some delicate maneuvering to not harm its delicate equipment. The rescue ship will spend a couple of weeks flying around the observatory, giving controllers time to plot the capture. Once latched on, the craft will boost the telescope back to its original altitude – allowing it to keep watching some of the most powerful events in the universe.

Script by Damond Benningfield

The Moon lines up with the twins of Gemini this evening – the stars Pollux and Castor. Pollux is the brighter twin, and is closer to the Moon. The brilliant planet Jupiter is to the lower right of the Moon.

Gemini has been around for thousands of years. Its roots trace back to ancient Babylon, as do those of many other constellations. All of them were recorded in one of the most important works of astronomy in the ancient world. Known as the Almagest, it was written by Claudius Ptolemy around the year 150.

Ptolemy studied many fields, including astronomy, astrology, geology, and music theory. The Almagest is perhaps his most famous work. In it, he recorded the positions of a thousand stars, and included details on the motions of the Sun, Moon, and planets. He also discussed everything from eclipses to the length of the year.

The book listed 48 constellations that were visible from northern skies – Gemini among them. The constellations weren’t given any borders – just the regions of the sky in which they appeared. And some barren regions weren’t part of any constellation.

Over the centuries, astronomers shifted things around some. And they created constellations for southern skies as well. Finally, in 1930, they created an “official” list of 88 constellations. Each one was given precise borders. That gave every star a home – its own “address” in the universe.

Script by Damond Benningfield

Hurricane season is whirling to life in the northern hemisphere. The giant storms twirl across the ocean, developing deadly winds, rains, and storm surges. As they grow, they trace a familiar pattern – cloud bands spinning counter-clockwise around the central eye.

That spin is a result of the Coriolis effect. It’s caused by a combination of Earth’s rotation and its shape.

Because Earth is a sphere, locations on the equator move more than 24,000 miles in 24 hours. Locations off the equator move a much smaller distance in the same time. So, as a storm moves across the northern hemisphere, its southern edge moves faster than its northern edge. This causes the storm to rotate counter-clockwise.

The Coriolis effect is much more pronounced on the giant worlds of the outer solar system – especially Jupiter. It’s the biggest planet, and it has the fastest rotation – one turn in less than 10 hours. That combination deflects what normally would be north-south winds into east-west winds. They can blow at hundreds of miles per hour. They separate Jupiter’s atmosphere into wide bands. Individual storms – some the size of continents or bigger – spin through the bands, or along their boundaries – monster storms spinning through alien skies.

Jupiter stands to the upper left of the Moon this evening. It looks like a brilliant star. The twins of Gemini are above the Moon, and we’ll have more about them tomorrow.

Script by Damond Benningfield