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Time-warp: Why June 30 will be a bit longer

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Alarm_Clocks_20101107a

Washington: Strictly speaking, a day lasts 86,400 seconds. On June 30, the day will officially be a bit longer than usual because an extra second or “leap” second will be added and NASA has an explanation for this.

“The Earth’s rotation is gradually slowing down a bit, so leap seconds are a way to account for that,” said Daniel MacMillan, NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

This is the case according to the time standard that people use in their daily lives – Coordinated Universal Time or UTC.

UTC is “atomic time” — the duration of one second is based on extremely predictable electromagnetic transitions in atoms of cesium.

These transitions are so reliable that the cesium clock is accurate to one second in 1,400,000 years.

However, the mean solar day — the average length of a day, based on how long it takes the Earth to rotate — is about 86,400.002 seconds long.

“That is because the Earth’s rotation is gradually slowing down a bit owing to a kind of braking force caused by the gravitational tug of war between the Earth, the Moon and the Sun,” the US space agency said in a statement.

Scientists estimate that the mean solar day has not been 86,400 seconds long since the year 1820 or so.

This difference of two milliseconds, or two thousandths of a second — far less than the blink of an eye — hardly seems noticeable at first.

But if this small discrepancy were repeated every day for an entire year, it would add up to almost a second.

Typically, a leap second is inserted either on June 30 or December 31.

Normally, the clock would move from 23:59:59 to 00:00:00 the next day. But with the leap second on June 30, UTC will move from 23:59:59 to 23:59:60, and then to 00:00:00 on July 1.

In practice, many systems are instead turned off for one second.

Previous leap seconds have created challenges for some computer systems and generated some calls to abandon them altogether.

“In the short term, leap seconds are not as predictable as everyone would like,” said Chopo Ma, geophysicist at Goddard.

“The modelling of the Earth predicts that more and more leap seconds will be called for in the long-term but we cannot say that one will be needed every year,” Ma said.

From 1972, when leap seconds were first implemented, through 1999, leap seconds were added at a rate averaging close to one per year.

Since then, leap seconds have become less frequent.

This June’s leap second will be only the fourth to be added since 2000.

(IANS)

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NASA’s human ‘computer’ is still working at age 80

Sue Finely calculated rocket trajectories by hand

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Sue Finley still works at NASA
Sue Finley, 80, is still working at NASA's Jet Propulsion Laboratory in Pasadena, California. She started there in 1958 as a human "computer," calculating trajectories for rockets. VOA

Sue Finley, now 80 years old and NASA’s longest-serving female employee, recalls her early days with the space agency when she worked as a human “computer,” calculating rocket trajectories by hand at a time when computers were huge and expensive to operate.

Finley arrived at Jet Propulsion Laboratory (JPL) in Pasadena, California, in January 1958, one week before the U.S. Army launched Explorer 1, America’s first earth satellite.

“It was a very big deal,” she recalls of the launch, a response to the launches a few months earlier of the first satellites, Sputnik 1 and 2, from the former Soviet Union.

She was at JPL for Pioneer 1, the first satellite sent aloft by the newly formed National Aeronautics and Space Administration (NASA) in late 1958, which marked the beginning of the international space race.

Unmanned space probes

Since then, Finley has had a role in nearly every U.S. unmanned space probe, and some missions of other nations.

There were failures to overcome and spectacular successes, but always new goals as scientists expanded our knowledge of the earth and solar system.

“We were certainly proud,” she says of NASA accomplishments, “but you just go to the next thing.”

Finley has been through several career changes with the space agency, one of the most important when NASA phased out human computers, moving, initially, to simple electronic versions.

“We got little tiny computers,” she recalls. “One I had 16 wires, jumper cables to code with. One had 10 pegboards that you programmed with.”

As modern computers took over navigational tasks, Finley developed and tested software as a subsystem engineer.

Among her career highlights: the Vega mission, a Soviet-French collaboration with Venus, and Halley’s Comet, which received navigational help from NASA and dropped balloons into the atmosphere of Venus.

She had to change the software for the antenna that tracked the mission, “and it worked,” Finley recalls. “Everything worked. That’s what was so exciting!”

Finley has worked since 1980 on NASA’s Deep Space Network, which coordinates satellite facilities in California, Spain and Australia that allow communication with space probes.

Highlights of NASA career

Career highlights include developing software that generates audio tones sent back from spacecraft, informing engineers on the ground what is happening in space. It was first developed for the Mars missions.

Each tone has a meaning that communicates data, noted one of Finley’s colleagues, Stephen Lichten.

“If a parachute opened, it would send a tone,” Lichten, manager for special projects for the Deep Space Network, said.

“The spacecraft lets go of its heat shield, and it would send a different tone, and so engineers like Sue were here listening for those special frequencies which told them the spacecraft was telling them what it has just done,” he said.

He notes that Finley also helped develop communication arrays that combine multiple antennas to act in unison and other advances that now crucial to space missions.

Lichten once shared an office with Finley and says she inspired her younger colleagues.

“There was a parade of people coming in constantly, to ask her advice, to ask her questions,” he recalls. “This was during the Venus balloon mission days and I realized that Sue was regarded as sort of a guru at JPL.”

Finley has been involved with nearly every advance in space communications in recent decades, and she continues her work today, Lichten said.

There are many more women at NASA today than there were when she started, and Finley said she tells young women to be inquisitive.

“I tell them to never be afraid to ask questions, never be afraid to say you don’t know,” she said.

After nearly six decades at the space agency, a mother of two grown sons and a mentor to her colleagues, Finley has no plans of retiring.

“There’s nothing else I want to do,” she said. “And so far, they need me.”

As they have since the earliest days of the space agency. (VOA)

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20 Years of Changing Seasons on Earth Captured into 2½ Minutes by NASA

NASA captured 20 years of changing seasons in a striking new global map of the home planet that shows Earth's fluctuations as seen from space

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The Changing seasons of the Earth
The Changing seasons of the Earth has been captured by NASA. Wikimedia.

NASA captured 20 years of changing seasons on Earth in a striking new global map of the home planet.

The data visualization, released this week, shows Earth’s fluctuations as seen from space.

The polar ice caps and snow cover are shown ebbing and flowing with the seasons. The varying ocean shades of blue, green, red and purple depict the abundance — or lack — of undersea life.

“It’s like watching the Earth breathe. It’s really remarkable,” said NASA oceanographer Jeremy Werdell, who took part in the project.

Two decades — from September 1997 to this past September — are crunched into 2½ minutes of viewing.

Werdell finds the imagery mesmerizing. “It’s like all of my senses are being transported into space, and then you can compress time and rewind it, and just continually watch this kind of visualization,” he said Friday.

Werdell said the visualization shows spring coming earlier and autumn lasting longer in the Northern Hemisphere. Also noticeable to him is the receding of the Arctic ice caps over time — and, though less obvious, the Antarctic, too.

On the sea side, Werdell was struck by “this hugely productive bloom of biology” that exploded in the Pacific along the equator from 1997 to 1998 — when a water-warming El Nino merged into cooling La Nina. This algae bloom is evident by a line of bright green.

In considerably smaller Lake Erie, more and more contaminating algae blooms are apparent — appearing red and yellow.

All this data can provide resources for policymakers as well as commercial fishermen and many others, according to Werdell.

Programmer Alex Kekesi of NASA’s Goddard Space Flight Center in Maryland said it took three months to complete the visualization, using satellite imagery.

Just like our Earth, the visualization will continually change, officials said, as computer systems improve, new remote-sensing satellites are launched and more observations are made. (VOA)

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NASA: Earth’s Ozone Hole Shrinks to Smallest Since 1988

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NASA
NASA: Earth's Ozone Hole Shrinks to Smallest Since 1988 (VOA)

Washington: The ozone hole over Antarctica shrank to its smallest peak since 1988, NASA said Thursday. The huge hole in Earth’s protective ozone layer reached its maximum this year in September, and this year NASA said it was 7.6 million square miles (19.6 million square kilometers). The hole size shrinks after mid-September.

This year’s maximum hole is more than twice as big as the United States, but it’s 1.3 million square miles smaller than last year and 3.3 million square miles smaller than 2015.

FILE - A false-color view of total ozone over the Antarctic pole is seen in this NASA handout image released Oct. 24, 2012. The purple and blue colors are where there is the least ozone. The average area covered by the Antarctic ozone hole in that year was the second smallest in two decades, at 8.2 million square miles; in September 2017, it was 7.6 million square miles.

[ FILE – A false-color view of total ozone over the Antarctic pole is seen in this NASA handout image released Oct. 24, 2012. The purple and blue colors are where there is the least ozone. The average area covered by the Antarctic ozone hole in that year was the second smallest in two decades, at 8.2 million square miles; in September 2017, it was 7.6 million square miles ].

Paul Newman, chief Earth scientist at NASA’s Goddard Space Flight Center, said stormy conditions in the upper atmosphere warmed the air and kept the chemicals chlorine and bromine from eating ozone. He said scientists haven’t quite figured out why some years are stormier — and have smaller ozone holes — than others.

“It’s really small this year. That’s a good thing,” Newman said.

Newman said this year’s drop is mostly natural but is on top of a trend of smaller steady improvements likely from the banning of ozone-eating chemicals in a 1987 international treaty. The ozone hole hit its highest in 2000 at 11.5 million square miles (29.86 million square kilometers).

Ozone is a colorless combination of three oxygen atoms. High in the atmosphere, about 7 to 25 miles (11 to 40 kilometers) above the Earth, ozone shields Earth from ultraviolet rays that cause skin cancer, crop damage and other problems.

Scientists at the United Nations a few years ago determined that without the 1987 treaty, by 2030 there would have been an extra 2 million skin cancer cases. They said that overall, the ozone layer is beginning to recover because of the phase-out of chemicals used in refrigerants and aerosol cans. (VOA)