Cassini saves daring maneuvers and observations for last

Cassini ring-grazing orbits. Image credit: NASA/JPL-Caltech

This graphic shows the closest approaches of Cassini’s final two orbital phases. Ring-grazing orbits are shown in gray (at left); Grand Finale orbits are shown in blue. The orange line shows the spacecraft’s Sept. 2017 final plunge into Saturn. Image credit: NASA/JPL-Caltech

NASA’s Saturn-orbiting Cassini spacecraft has made its first close dive past the outer edges of Saturn’s rings since beginning its penultimate mission phase on Nov. 30.

Cassini crossed through the plane of Saturn’s rings on Dec. 4 at 8:09 AM EST at a distance of approximately 57,000 miles (91,000 kilometers) above Saturn’s cloud tops. This is the approximate location of a faint, dusty ring produced by the planet’s small moons Janus and Epimetheus, and just 6,800 miles (11,000 kilometers) from the center of Saturn’s F ring.

About an hour prior to the ring-plane crossing, the spacecraft performed a short burn of its main engine that lasted about six seconds. About 30 minutes later, as it approached the ring plane, Cassini closed its canopy-like engine cover as a protective measure.

“With this small adjustment to the spacecraft’s trajectory, we’re in excellent shape to make the most of this new phase of the mission,” said Earl Maize, Cassini project manager at NASA’s Jet Propulsion Laboratory, Pasadena, California.

A few hours after the ring-plane crossing, Cassini began a complete scan across the rings with its radio science experiment to study their structure in great detail.

“It’s taken years of planning, but now that we’re finally here, the whole Cassini team is excited to begin studying the data that come from these ring-grazing orbits,” said Linda Spilker, Cassini project scientist at JPL. “This is a remarkable time in what’s already been a thrilling journey.”

Cassini’s imaging cameras obtained views of Saturn about two days before crossing through the ring plane, but not near the time of closest approach. The focus of this first close pass was the engine maneuver and observations by Cassini’s other science instruments. Future dives past the rings will feature some of the mission’s best views of the outer regions of the rings and small, nearby moons.

Each of Cassini’s orbits for the remainder of the mission will last one week. The next pass by the rings’ outer edges is planned for Dec. 11. The ring-grazing orbits — 20 in all — will continue until April 22, when the last close flyby of Saturn’s moon Titan will reshape Cassini’s flight path. With that encounter, Cassini will leap over the rings, making the first of 22 plunges through the 1,500-mile-wide (2,400-kilometer) gap between Saturn and its innermost ring on April 26.

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October Meeting: Relativity & election nominations

by William Murmann, CAA President

Tonight is our monthly CAA meeting Monday night (Oct. 10) — 7:30 PM at the Rocky River Nature Center. CAA member Bob Fritz will give a talk at 7:30 entitled “General Relativity: What It Is and Why It Matters.”

After Bob’s presentation and our break we will have our monthly business meeting and the first nominations for election to officer and member-at-large positions. Second nominations and the election will be held at our November 14 meeting.

Under our club bylaws, voting privileges start after six months of membership. Any member in good standing can run for a member-at-large position on the Board. Candidates for the office of president, vice president, secretary, and treasurer shall be limited to members who have been CAA members for at least two years, and who have attended at least half of the membership meetings during the preceding two years, or who are recommended by the Board.

The CAA Board consists of the four executive officers and the three members-at-large.

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Great food, friendship, observing, and prizes at annual convention

Our rescheduled September 24 OTAA Convention was a success with great weather, good food, starry skies, and good times! The event took place at the CAA’s observing site in the Medina County Park System’s Letha House Park West. Many thanks go out to the generous CAA officers and members who worked diligently to make the event happen.

The Cuyahoga Astronomical Association would also like to thank the following vendors for their donations raffle prizes for the convention:

Astrozap
P.O. Box 502
Lakewood, OH 44107

Bob’s Knobs
6976 Kempton Rd.
Centerville, IN 47330

Knightware
305 Evans Estates Drive
Cary, North Carolina 27513

Oceanside Photo & Telescope
918 Mission Avenue
Oceanside, CA 92054

Orion Telescopes & Binoculars
89 Hangar Way
Watsonville, CA 95076

Tele Vue Optics, Inc.
32 Elkay Dr.
Chester, NY 10918

Yes, our next OTAA Convention is already scheduled: Saturday, August 19, 2017. See you then?

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Earth-sized world detected at Proxima Centauri

Astronomers using ESO telescopes and other facilities have found clear evidence of a planet orbiting the nearest star to our own Sun, Proxima Centauri. The long-sought world, designated Proxima b, orbits its cool red parent star every 11 days and has a temperature possibly suitable for liquid water to exist on its surface. This rocky world is a little more massive than the Earth and is the closest exoplanet to us — and it may also be the closest possible abode for life outside the Solar System. A paper describing this milestone finding will be published in the journal Nature on 25 August 2016.

Just over four light-years from the Solar System lies the red dwarf star named Proxima Centauri as it is the closest star to Earth apart from the Sun. This cool star, in the southern hemisphere constellation of Centaurus, is too faint to be seen with the unaided eye and lies near to the much brighter pair of stars known as Alpha Centauri AB.

During the first half of 2016 Proxima Centauri was regularly observed with the HARPS spectrograph on the ESO 3.6-metre telescope at La Silla in Chile and simultaneously monitored by other telescopes around the world. This was the Pale Red Dot Campaign, in which a team of astronomers led by Guillem Anglada-Escudé, from Queen Mary University of London, was looking for the tiny back and forth wobble of the star that would be caused by the gravitational pull of a possible orbiting planet.

As this was a topic with very wide public interest, the progress of the campaign between mid-January and April 2016 was shared publicly as it happened on the Pale Red Dot website and via social media. The reports were accompanied by numerous outreach articles written by specialists around the world.

Guillem Anglada-Escudé explains the background to this unique search: “The first hints of a possible planet were spotted back in 2013, but the detection was not convincing. Since then we have worked hard to get further observations off the ground with help from ESO and others. The recent Pale Red Dot campaign has been about two years in the planning.”
The Pale Red Dot data, when combined with earlier observations made at ESO observatories and elsewhere, revealed the clear signal of a truly exciting result.

At times Proxima Centauri is approaching Earth at about five kilometers per hour — normal human walking pace — and at times receding at the same speed. This regular pattern of changing radial velocities repeats with a period of 11.2 days. Careful analysis of the resulting tiny Doppler shifts showed that they indicated the presence of a planet with a mass at least 1.3 times that of the Earth, orbiting about seven million kilometers from Proxima Centauri — only five percent of the Earth-Sun distance.

Guillem Anglada-Escudé comments on the excitement of the last few months: “I kept checking the consistency of the signal every single day during the 60 nights of the Pale Red Dot Campaign. The first 10 were promising, the first 20 were consistent with expectations, and at 30 days the result was pretty much definitive, so we started drafting the paper!”

Red dwarfs like Proxima Centauri are active stars and can vary in ways that would mimic the presence of a planet. To exclude this possibility the team also monitored the changing brightness of the star very carefully during the campaign using the ASH2 telescope at the San Pedro de Atacama Celestial Explorations Observatory in Chile and the Las Cumbres Observatory telescope network. Radial velocity data taken when the star was flaring were excluded from the final analysis.

Although Proxima b orbits much closer to its star than Mercury does to the Sun in the Solar System, the star itself is far fainter than the Sun. As a result Proxima b lies well within the habitable zone around the star and has an estimated surface temperature that would allow the presence of liquid water. Despite the temperate orbit of Proxima b, the conditions on the surface may be strongly affected by the ultraviolet and X-ray flares from the star — far more intense than the Earth experiences from the Sun.

Two separate papers discuss the habitability of Proxima b and its climate. They find that the existence of liquid water on the planet today cannot be ruled out and, in such case, it may be present over the surface of the planet only in the sunniest regions, either in an area in the hemisphere of the planet facing the star (synchronous rotation) or in a tropical belt (3:2 resonance rotation). Proxima b’s rotation, the strong radiation from its star and the formation history of the planet makes its climate quite different from that of the Earth, and it is unlikely that Proxima b has seasons.

This discovery will be the beginning of extensive further observations, both with current instruments and with the next generation of giant telescopes such as the European Extremely Large Telescope (E-ELT). Proxima b will be a prime target for the hunt for evidence of life elsewhere in the Universe. Indeed, the Alpha Centauri system is also the target of humankind’s first attempt to travel to another star system, the StarShot project.

Guillem Anglada-Escudé concludes: “Many exoplanets have been found and many more will be found, but searching for the closest potential Earth-analog and succeeding has been the experience of a lifetime for all of us. Many people’s stories and efforts have converged on this discovery. The result is also a tribute to all of them. The search for life on Proxima b comes next…”

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Milky Way stars during public star party

Photo: Looking South Along the Lake at Letha House Park, Milky Way Glowing Overhead, the Moon Sinking Low in the West. Photo by Alan Studt.

Looking South Along the Lake at Letha House Park, Milky Way Glowing Overhead. Photo by Alan Studt. Nikon D810: ISO 3200, 13 sec., f/2.8, 14mm.

We had great sky conditions for our August 6 public star party at Letha House Park. We didn’t get an exact count, but I think there were between 75 and 100 guests who came for the program, including Park Ranger Bob who stopped by to say hello.

I had to make a quick count in the dark, but I think we had about 12 telescopes for this Medina County Park District program. Two telescopes were brought by new members who I believe joined one of our star parties for the first time.

Many thanks to Dave Nuti, Chris Christe, Bruce Lane, Jay Reynolds, Nora Mishey, Carl Kudrna, Rich & Nancy Whisler, Bob Wiersma, Alan Studt, Rob Seig, Bob & Mary Deep, and Gale Franko who joined me to help with the program!

Thanks to Jay, who manned the observatory and gave our new 12-inch go-to scope a workout to show the night sky to our numerous  guests.  And thanks also to Nora, who brought delicious homemade cookies and her astronomy Q & A display, and who served as a host in the building to help promote our club and the park district’s programs.

Reported by William Murmann, CAA President

Photo: Summer Milky Way. Photo by Alan Studt.

Summer Milky Way. Photo by Alan Studt. Nikon D810: ISO 5000, 15 sec., f/2.8, 14mm.

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Public Observing Saturday, August 6

The Cuyahoga Astronomical Association’s (CAA’s) observatory at Letha House Park will be open for public observing Saturday, August 6, from 8:30 to 11:00 PM. Visitors will be treated to telescopic views of the Moon (early), Saturn, and as the sky darkens, deep sky objects such as star clusters. Mars may also be viewed but is becoming more distant from Earth and offers less detail to viewers. Click here for our observatory’s web page for information on how to get to the observatory and advice on attending a star party.

The observatory is operated in cooperation with the Medina County Park District (which owns the property). Restroom facilities are available at the park and, in the event of cloudy or inclement weather, an indoor astronomy program will be offered in place of outdoor observing.

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Rescheduled OTAA Convention: September 24

The CAA’s annual OTAA Convention event has been rescheduled to take place on September 24, 2016 at Letha House Park West; registration should begin at 3:00 PM. The gathering was to have been held July 30 but a scheduling issue prevented it taking place.

Socializing, a cookout, door prize raffle, astronomy talk, and (weather permitting) star party are planned for the day and night. Members of the CAA and other regional astronomy clubs are invited to attend. In the event of cloudy or inclement weather, all events except for stargazing will take place.

Image: All-Sky Map, September 24, 2016

All-Sky Map, September 24, 2016 – Click to Embiggen

Letha House Park West features an enclosed, heated and air conditioned event building with modern lighting, projection equipment, and restrooms. The CAA maintains its observatory at Letha House Park and that facility will be open during the star party. The parking lot is paved and a large, grassy area adjacent to the lot makes for easy telescope setup. Nighttime skies are good (considering the Northeastern Ohio location) allowing for rewarding observations.

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