Bringing new life to Laser Guide Star

The Lick Observatory’s Laser Guide Star forms a beam of glowing atmospheric sodium ions. This helps astronomers account for distortions caused by the Earth’s atmosphere so they can see further and more clearly into space.

Earlier this year, Lawrence Livermore engineering technical associate Pam Danforth applied 30 years of laser experience to an out-of-this-world problem — bringing new life to the University of California’s
The Lick Observatory’s Laser Guide Star is vital to astronomers because a natural guide star isn’t always near an object they want to observe. By training the guide star beam into the sky near such an object, an artificial guide star of glowing atmospheric sodium ions is created, allowing the laser guide star to function like a natural guide star and provide correct focus for the object they want to observe.

The Laser Guide Star was a spin-off technology from LLNL’s Atomic Vapor Laser Isotope Separation (AVLIS) program, a project Danforth worked on for nearly 20 years. Her specialty was the program’s dye master oscillator. The dye master oscillator provides precise laser frequency and pulse length for the dye amplifiers.

In addition, Danforth was part of the design team for the two Laser Guide Star systems that are used at both the Lick Observatory and Hawaii’s Keck Observatory. She also was part of the team that installed the system at Keck and prepared the system for use by Lick Observatory staff.

“I have always been enthusiastic about helping astronomers see further and more clearly into space. I enjoyed being part of this developmental effort for many years,” Danforth said. “To be able to make a dramatic impact on the world of astronomy was very exciting.”

It was this combined expertise that made Danforth the right person to help bring the Laser Guide Star back to peak operating condition. According to Lick Observatory Superintendent Kostas Chloros, this work was needed as the system’s performance and efficiency had degraded, impacting the research programs that require the use of a laser guide star.

“Pam and the rest of the team are experts on this laser system,” Chloros said. “Their work from over a decade ago produced a very reliable, robust and stable system, which made operations go smoothly over the years. But a good, precise tune-up was due.”

The low power problem was found to originate at the master oscillator and a burned dye cell. When Danforth evaluated the grazing incidence dye master oscillator (GIDMO) she found it had two significant burns. She was able to locate another viable upstream position. This new dye cell position required a major disassembly and realignment of the GIDMO.

Danforth was able to reposition the grating and realign the GIDMO to the peak of the sodium signal. She also identified several external factors contributing to the low power out of the GIDMO and lower conversion efficiency in the amplifiers.

According to Chloros, this work increased the single frequency power out of the master oscillator dramatically, enabling a higher power and a broader pulse to be delivered to the amplifiers. The overall output power of the laser system was 2-3 times higher.

“As a result, the brighter sodium guide star produces a good reference signal for the newly-developed Shane Adaptive Optics system, and it has benefited other research groups and their projects, as well as new instrument development that takes place at Lick,” he said.

The Lick Observatory, situated on the summit of Mount Hamilton, is an astronomical observatory owned and operated by the University of California. It is the world's first permanently occupied mountain-top observatory.

The Lick Observatory, situated on the summit of Mount Hamilton, is an astronomical observatory owned and operated by the University of California. It is the world’s first permanently occupied mountain-top observatory.

Source:Lawrence Livemore National Laboratory

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Saturn:Planet with the rings

Saturn is the sixth planet from the sun and the second largest planet in the solar system. Although the other gas giants in the solar system — Jupiter, Uranus and Neptune — also have rings, those of Saturn are without a doubt the most extraordinary.

Saturn was the Roman name for Cronus, the lord of the Titans in Greek mythology. Saturn is the root of the English word “Saturday.”

Physical characteristics of Saturn

Saturn is a gas giant made up mostly of hydrogen and helium. Saturn is big enough to hold more than 760 Earths, and is more massive than any other planet except Jupiter, roughly 95 times Earth’s mass. However, Saturn has the lowest density of all the planets, and is the only one less dense than water — if there were a bathtub big enough to hold it, Saturn would float.

Saturn is the farthest planet from Earth visible to the naked human eye. The yellow and gold bands seen in Saturn’s atmosphere are the result of super-fast winds in the upper atmosphere, which can reach up to 1,100 mph (1,800 kph) around its equator, combined with heat rising from the planet’s interior.

Saturn spins faster than any other planet except Jupiter, completing a rotation roughly every 10-and-a-half hours. This rapid spinning causes Saturn to bulge at its equator and flatten at its poles — the planet is 8,000 miles (13,000 km) wider at its equator than between the poles.

Saturn’s most recent curiosity may be the giant hexagon circling its north pole, with each of its sides nearly 7,500 miles (12,500 km) across — big enough to fit nearly four Earths inside. Thermal images show it reaches some 60 miles (100 km) down into the planet’s atmosphere. It remains uncertain what causes it.

Composition & structure

Atmospheric composition (by volume)

96.3 percent molecular hydrogen, 3.25 percent helium, minor amounts of methane, ammonia, hydrogen deuteride, ethane, ammonia ice aerosols, water ice aerosols, ammonia hydrosulfide aerosols

Magnetic field

Saturn has a magnetic field about 578 times more powerful than Earth’s.

Chemical composition

Saturn seems to have a hot solid inner core of iron and rocky material surrounded by an outer core probably composed of ammonia, methane, and water. Next is a layer of highly compressed, liquid metallic hydrogen, followed by a region of viscous hydrogen and helium. This hydrogen and helium becomes gaseous near the planet’s surface and merges with its atmosphere.

Internal structure

Saturn seems to have a core between about 10 to 20 times as massive as the Earth.

Orbit & rotation

Average distance from the sun: 885,904,700 miles (1,426,725,400 km)
By Comparison: 9.53707 times that of Earth

Perihelion (closest approach to sun): 838,519,000 miles (1,349,467,000 km)
By Comparison: 9.177 times that of Earth

Aphelion (farthest distance from sun): 934,530,000 miles (1,503,983,000 km)
By Comparison: 9.886 times that of Earth

Image

Saturn’s moons

Saturn has at least 62 moons. Since the planet was named after Cronus, lord of the Titans in Greek mythology, most of Saturn’s moons are named after other Titans, their descendants, as well as after giants from Gallic, Inuit and Norse myths.

Saturn’s largest moon, Titan, is slightly larger than Mercury, and is the second-largest moon in the solar system behind Jupiter’s moon Ganymede. Titan is veiled under a very thick, nitrogen-rich atmosphere that might be like what Earth’s was long ago, before life. While the Earth’s atmosphere extends only about 37 miles (60 km) into space, Titan’s reaches nearly 10 times as far.

These moons can possess bizarre features. Pan and Atlas are shaped like flying saucers, Iapetus has one side as bright as snow and one side as dark as coal, and Enceladus shows evidence of “ice volcanism,” spewing out water and other chemicals. A number of these satellites, such as Prometheus and Pandora, are shepherd moons, interacting with ring material to keep rings in their orbits.

Saturn’s rings

Galileo Galilei was the first to see Saturn’s rings in 1610, although from his telescope they resembled handles or arms. It took Dutch astronomer Christiaan Huygens, who had a more powerful telescope, to propose that Saturn had a thin, flat ring.

Saturn actually has many rings made of billions of particles of ice and rock, ranging in size from a grain of sugar to the size of a house. The largest ring spans up to 200 times the diameter of the planet. The rings are believe to be debris left over from comets, asteroids or shattered moons. Although they extend thousands of miles from the planet, the main rings are typically only about 30 feet thick. The Cassini-Huygens spacecraft revealed vertical formations in some of the rings, with particles piling up in bumps and ridges more than 2 miles (3 km) high.

The rings are generally named alphabetically in the order they were discovered. They are usually relatively close to each other, with one key exception caused by the Cassini Division, a gap some 2,920 miles (4,700 km) wide. The main rings, working out from the planet, are known as C, B and A, with the Cassini Division separating B and A. The innermost is the extremely faint D ring, while the outermost to date, revealed in 2009, could fit a billion Earths within it.

Mysterious spokes have been seen in Saturn’s rings, which might form and disperse over a few hours. Scientists have conjectured these spokes might be composed of electrically charged sheets of dust-sized particles created by small meteors impacting the rings or electron beams from the planet’s lightning. Saturn’s F Ring also has a curious braided appearance — it is composed of several narrow rings, and bends, kinks, and bright clumps in them can give the illusion that these strands are braided.

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