Tag Archives: Seattle Astronomical Society

Herschel’s observation of comets

To say that Woody Sullivan is interested in William Herschel would be quite an understatement.

“I have dressed up as Herschel for Astronomy 101 half a dozen times,” said Sullivan, a professor emeritus of astronomy at the University of Washington. He started a file on Herschel, the 18th and 19th Century astronomer, some 30 years ago, but can’t exactly pin down why he was so drawn to him.

“I have eclectic interests,” Sullivan said. “I’m always looking for what I call astronomy on the edges: astronomy and music, astronomy and astrology, history, literature, sundials.”

“Herschel was that way to some degree,” Sullivan added. “Perhaps that was it; I saw a fellow traveler there.”

Woody Sullivan

Prof. Woody Sullivan at the May meeting of the Seattle Astronomical Society. (Photo: Greg Scheiderer)

Sullivan noted that it was nine years ago that he started doing more serious research into Herschel with the intent to write a biography. While there have been many penned, including a couple in the last decade or so, Sullivan noted that none have been particularly scholarly, and so that’s a void he’s aiming to fill. After all of that research, the actual writing has begun.

“I do need to get on because I’m getting on,” Sullivan quipped. He spoke about his work at the most recent meeting of the Seattle Astronomical Society, discussing Herschel’s work on comets, about which few biographers have gone into much detail.

While his sister Caroline Herschel discovered eight comets, six of which bear her name, William never found one, though he came close a couple of times. He once reported a comet discovery, but the French astronomer Jean-Louis Pons had already found it a month before. Then in 1781 Herschel reported another comet discovery. But after six or eight months of observation, astronomers more skilled in the calculation of orbits found this new object to be in a nearly circular one well beyond Saturn’s. It was a new planet: Uranus.

First to “discover” a planet

“It’s hard to think about what a new planet means. What planets did we have before? We had the same planets that we had had since Ogg the caveman,” Sullivan noted. “Herschel was the first one to find a planet telescopically, and this made him instantly famous.”

William Herschel

William Herschel. (Photo: Public domain)

Herschel parlayed that into a gig as the court astronomer for King George III. It was actually a pay cut from Herschel’s work as a professional musician in Bath, but he supplemented his income by building and selling telescopes, and by marrying a rich widow. Herschel was mostly interested in deep-sky objects, but comets came to his attention on occasion, in part because he was interested in change.

“A comet is change par excellence,” Sullivan said. “It just appears in the sky, it’s different every day, you never know what’s going to happen.”

While Caroline wanted to discover them, William aimed to understand what they were. Sullivan noted that this wasn’t what most astronomers were doing then.

A different sort of astronomer

“Astronomy at that time was measuring accurate positions of things; planets and their moons and comets and stars for catalogs,” he said. “That’s why you had the Greenwich Observatory. The government was paying for that, not because they loved astronomy but they loved the navy, and you needed that for navigation.”

Herschel’s observations of the great comets of 1807 and 1811 were interesting. Sullivan pointed out that astronomers at the time thought there might be a planet or other object at the nucleus of a comet. Herschel was the first to claim he’d spotted one. When others couldn’t find it, Herschel chalked it up to the superior optics of his telescope. By the 1811 comet, he was trying to figure out if the nucleus reflected light from the Sun, or generated its own light. Herschel declared that the nucleus of this comet was perfectly round, and thus self-illuminated, because if it reflected light it would show phases. Sullivan, after poring through Herschel’s logs, concluded that he had fallen into a trap that scientists need to avoid.

“There’s just no doubt that he was picking and choosing the observations that fit into his concept,” Sullivan said. It was a bit of a reach to claim to be able to determine the roundness of an object of perhaps an arcsecond in width within the fuzzy coma of a comet.

“He’s getting all of his theory and observations mixed up,” Sullivan said. “This can get you in trouble.”

Though Herschel missed on this particular analysis, Sullivan noted that Herschel made some interesting conclusions, particularly in describing the tail of a comet as its atmosphere being pushed away by pressure from the Sun. Though it’s not the atmosphere, but dust and gasses, nobody to that point had really postulated that the Sun might be pushing on things. Other descriptions Herschel made of the mechanics of comets are not so far off from what is held true today.

Sullivan’s presentations are always interesting, and we look forward to the completion of the book and to learning about William Herschel, a fascinating character in the history of science.



Causing mayhem and mass destruction in the Universe Sandbox

If you’ve ever wondered what would happen if the Sun somehow vanished from the solar system, or wanted to watch planets smash into each other, or thought it would be fun to bombard the Moon with asteroids, you’re in luck! You can do all of those things and more with a computer game called Universe Sandbox2. Dan Dixon, creator of Universe Sandbox2, gave a demonstration of it at this week’s meeting of the Seattle Astronomical Society.

“It is software that allows you to ask fantastical questions about the universe and see plausibly true answers,” Dixon said.

Universe Sandbox2 sells for $25.

The possibilities are vast. The slogan for Universe Sandbox2 is “create & destroy on an unimaginable scale,” and the software delivers. It lets users tinker with an incredible number of variables, from the mass and density of objects to the chemical makeup of their atmospheres. Eliminate all of the carbon dioxide and see what happens! Move the Moon in closer to Earth and watch the chaos. For all of the interesting science questions it can answer, Universe Sandbox2 also appeals to our inner 12-year-old.

“People like to collide things,” Dixon noted, and clearly he is one of those people.

“It’s a physics simulation, so in addition to doing interesting things with orbits, you can also do interesting things with collisions,” he added.

Universe Sandbox screenshot

Screenshot from Universe Sandbox2 of an object colliding with Earth.

Those mash-ups got a lot of oohs and aahs from the attendees at the meeting at the University of Washington. It was fun to see what Earth would do to the ring system if it were placed in orbit around Saturn. (Spoiler alert: Disruptive!) Dixon raced through dozens of scenarios, and that only scratched the surface.

He said the results shown in Universe Sandbox2 are “plausibly” true because they have to make some compromises. They don’t simulate every object or every particle out there because that would take way too much computer oomph.

Plausibly true

“It’s a very simplistic simulation; we’re not doing any pressure waves or dark matter,” Dixon said, “but it still is pretty cool.”

So when Mars smacks into Earth in an attempt to see if a new moon would result, you don’t necessarily have all of the data you would like.

“You really would want to have like a billion pieces,” Dixon said, but “because we’re trying to do this real time on modern-day desktops or laptops, you can’t have as many pieces as you want and get it still to run in real time.”

“We’re undoubtedly wrong in a lot of cases, and there’s a lot of room for improvement in the simulation,” Dixon noted. They’re revamping the way the program handles stellar evolution and are working to improve planetary climate simulations. Part of the challenge is that they’re often simulating events for which there is not yet a scientific answer.

“We’re trying to solve things that are not well-defined or understood,” Dixon said. That’s not to say they’re just making stuff up.

“Being realistic is really important to me,” Dixon said, but they want to let users come up with their own crazy scenarios. “One of the goals of the software is to allow ridiculous premises but then carry that to a realistic conclusion.”

Humble beginnings

In a way, Universe Sandbox2 has been in development for 20 years. When Dixon was in middle school his father downloaded a simple gravity simulator from a BBS list. (Remember those?) It didn’t have many features, but it caught Dixon’s interest.

“I’ve always been fascinated with the motions of gravity,” he said, “and gravity is a really simple formula, too. It’s always fascinating how this really simple formula can do these really beautiful and organic interesting motions.” Later on in middle school Dixon coded his own simulator. He’d tinker with it every once in a while, then became serious about it about ten years ago.

“This was not like the grand ambition. It was a thing I was working on for fun, and now it’s turned into this crazy thing,” Dixon said. “What started as a personal side project is now what myself and eight others do full time.”

“I think if I had a time machine and I went back and showed my younger self what it’s become, I would have been overwhelmed and wouldn’t have started on it,” he laughs.

“This is a passion project that I’m fortunate enough to continue working on.”

View the Universe Sandbox2 teaser below. Purchasing through this link supports not only Universe Sandbox2 but also Seattle Astronomy in our efforts to tell interesting stories.


Threading the needle with Cassini at Saturn

The hugely successful Cassini mission to Saturn will come to a fiery end in September, and you can hardly blame NASA for going a little Star Trek on us.

Ron Hobbs

Ron Hobbs. Photo: Greg Scheiderer.

“We’re going somewhere where no spacecraft has ever gone before, into this region between the glorious rings of Saturn and the cloud tops of the planet,” said Ron Hobbs, a NASA Solar System Ambassador, at this month’s meeting of the Seattle Astronomical Society. After 22 orbits through the eye of that needle—a 2,500-kilometer-wide gap—they’ll splat Cassini into the planet and burn it up.

“Now that we’ve discovered that there’s at least one moon, and maybe several, that could have the conditions for life, it’s very important to not leave a derelict spacecraft orbiting around Saturn,” Hobbs noted. “One of the important things at the end of the solstice mission will be to dispose of the spacecraft.”

The second extended mission of Cassini was named solstice because it is almost the beginning of summer in Saturn’s northern hemisphere.

Let’s do science

Before they crash Cassini, they figured there was some time to do some great science in that place where no spacecraft has ever gone. Most importantly, they will get a better picture of the internal structure of Saturn and examine its ionosphere, inner radiation belts, and auroral region.

“This would have been worth sending a spacecraft to Saturn for just that measurement,” Hobbs said, noting that it is essentially what Juno is doing at Jupiter. They’ll also check out the particles of Saturn’s D ring at close range, and be able to better gauge the mass of the ring system, which will help pin down its age.

“I can’t wait for the pictures,” Hobbs added. “The pictures that come out of this mission are just going to be spectacular.”

Shooting the gap

Hobbs said NASA has been using interactions between Cassini and Saturn’s moon Titan to nudge the spacecraft’s orbit to where they want it to be.

“Titan is really the only object in Saturn orbit that has enough mass to allow it to do gravitational assists and re-direct its orbit,” he said. “That allows [Cassini] to change its orbit and change the plane of its orbit.”

Cassini orbits

This graphic shows the closest approaches, or periapses, of Cassini’s final two orbital phases.The ring-grazing orbits are shown in gray; grand finale orbits are shown in blue. The orange line shows the spacecraft’s final plunge into Saturn. Credit: NASA / Jet Propulsion Laboratory – Caltech

In late November a brush with Titan dropped Cassini’s perichron—the point closest to Saturn in its orbit around the planet—down to just outside the F ring. In April, another Titan flyby will drop that perichron down to between the D ring and Saturn’s cloud tops.

“That’s when it’s going to get really exciting,” Hobbs said. Cassini will do 22 “grand finale” orbits through the eye of this needle, each lasting six days, collecting science data until one final encounter with Titan puts the spacecraft on a trajectory to splat into the planet on September 15.

It’s amazing how much planning and politics went into all of this. Hobbs said the actual trajectories of the orbits for this grand finale were determined a little over three years ago. Ever since then there’s been a spirited discussion between scientists, engineers, and mission leaders about what science to do to get as much data as possible out of the final mission. That determination was just completed last month.

“The spacecraft drivers are now writing the code for these orbits,” Hobbs said. That will tell Cassini where to go and where to point its instruments to make the observations as planned.

A good ride

Hobbs noted that Cassini was launched in October 1997, and so will end its mission just shy of twenty years in space.

“Without a doubt it has been one of the most successful and audacious missions NASA and the international community have operated,” he said. “This is going to be one of the highlights of space exploration in the last couple of decades.”


Kelly Beatty’s history of Pluto

The history of Pluto goes way back before it became a tiny twinkle in Clyde Tombaugh’s blink comparator. Kelly Beatty, a senior editor at Sky & Telescope magazine, told the story of Pluto in his keynote address Saturday at the annual banquet of the Seattle Astronomical Society.

Scheiderer and Beatty

Kelly Beatty, right, with Seattle Astronomy’s Greg Scheiderer at the annual banquet of the Seattle Astronomical Society January 28, 2017. Astronomy guys love their astronomy ties. Photo: Greg Scheiderer.

In a way, according to Beatty, the hunt for Pluto dates back to the late 1700s. The Titius–Bode law (since repealed) of the distances to the planets from the Sun worked well, with one exception: according to the law, there should be a planet between Mars and Jupiter. Thus a group of astronomers calling themselves the “celestial police,” led by Franz Xaver von Zach, set out to find this elusive object. They did it; on New Year’s Day, 1801, Giuseppe Piazzi discovered Ceres. It wasn’t long before Juno, Vesta, and Pallas we found. At first all four were labeled planets, but now they’re known as the four largest asteroids—and possibly the first celestial objects to be demoted in status.

Dumb, fool luck

Lowell blink comparator

Blink comparator used by Clyde Tombaugh at Lowell Observatory to discover Pluto. Photo: © User:Pretzelpaws / Wikimedia Commons / CC-BY-SA-3.0.

Later, because of irregularities in the motion of Uranus, astronomers predicted another planet out beyond its orbit. But even after the discovery of Neptune in 1846, anomalies remained. Percival Lowell and William Pickering predicted there was yet another planet beyond Neptune. The hunt was on for Planet X, and Pluto was finally discovered by Clyde Tombaugh in 1930. We soon learned that Pluto was pretty small, which lent some irony to its discovery.

“Pluto didn’t have any effect on Uranus and Neptune at all,” Beatty said. “It turns out that the mathematics were incorrect, the positional accuracy of those early observations was bad. There was no basis to the prediction whatsoever, and by dumb, fool luck Clyde found the planet Pluto that he had been seeking within about six degrees of the predicted position. Freakingly by accident.”

We didn’t know a whole lot about Pluto for a long time. The best photos we could get were fuzzy Hubble Space Telescope shots. Astronomers found methane ice on Pluto in 1976, and its moon Charon was discovered in 1978. Pluto’s atmosphere was discovered in 1988 when it occulted a star.

Pluto on thin ice

“In 1998 the bottom fell out of the pro-Pluto movement,” Beatty said. The beginning of the end was the discovery of another distant object in what we now call the Kuiper Belt. Astronomers figured that there had to be more out there than just Pluto, and we now know of more than 1,800 of them. Many of these objects are locked in a 3:2 orbital resonance with Neptune, just like Pluto.

“Not only is Pluto not alone, it’s not even unique in its orbit,” Beatty said. “Things did not look good for Pluto and its planet status.”

The International Astronomical Union (IAU) started hearing chatter that Pluto should not be a planet, and in 1999 it passed a resolution declaring that it still was. Brian Marsden, who headed the minor planet center of IAU, really wanted to classify Pluto as an asteroid, according to Beatty.

Then, in 2005, Eris was discovered. At the time it appeared to be bigger than Pluto, though we now know it is slightly smaller. It was bureaucracy that finally knocked Pluto off the planet list. Different committees at the IAU name planets and asteroids, so to decide to which committee to refer the new discovery for naming, they had to decide what it was. This led to the new definition of planet, under which neither Eris nor Pluto fall. The IAU declared Pluto to be a dwarf planet in 2006.

Beatty is not fond of the IAU definition of planet: an object that orbits the Sun, has enough mass to be round, and has “cleared the neighborhood of its orbit.”

“It’s a really stupid definition,” Beatty said, mostly because it’s hard to know the mass of faraway objects, and so the definition is difficult to apply. Plus he finds it puzzling that a dwarf planet is not a planet.

“We have dwarf stars which are considered stars.” he pointed out. “We have dwarf galaxies that are considered galaxies. A chihuahua is still a dog.”

New Horizons


New Horizons close-up of Pluto, one of the first and most iconic images from the mission. Photo: NASA.

Planet or not, the New Horizons flyby of Pluto in 2015 gave us a ton of new information about it and its moons. Beatty shared numerous photos of and findings about Pluto from the mission. It’s mostly made of rock, and might have liquid water below its surface. The surface features are mostly hard-frozen water ice, with a little frozen nitrogen, methane, and carbon dioxide mixed in.

Most fascinating is evidence of geology happening right now in the form of flowing nitrogen ice.

“Pluto’s surface, against all odds, out in the frozen corner of the solar system,” Beatty marveled, “has flowing glaciers on it.”

The last of the Pluto data from New Horizons arrived on Earth back in October, but the mission isn’t over. The probe is headed out for a look at the Kuiper Belt object 2014 MU69, at which it will arrive on January 1, 2019.

Beatty said this great new data about Pluto was worth the wait.

“We finally know what this planet/dwarf planet/interesting world looks like,” he said. “It was a 30-year effort from the time the Pluto missions were first conceived until we finally got out there. Some of the people involved, like Alan Stern, were there every year of the way, and boy, what a rich reward they have for their efforts.”


LIGO and the era of multimessenger astronomy

Multimessenger astronomy is a fairly new buzz word in the science. Dr. Joey Key, an assistant professor of physics at the University of Washington Bothell and a member of the LIGO Scientific Collaboration, talked about the concept at last month’s meeting of the Seattle Astronomical Society.

Joey Key

Dr. Joey Key of the UW Bothell gave a talk about LIGO and the era of multimessenger astronomy at the Dec. 21 meeting of the Seattle Astronomical Society. Key made the same presentation to the Everett Astronomical Society Jan. 7. Photo: Greg Scheiderer.

As you probably know LIGO—the Laser Interferometer Gravitational-wave Observatory—made the first detection of gravitational waves, as predicted by Einstein’s theory of general relativity, back in December 2015 and announced the findings last February. So now what?

“The next big goal for LIGO is to have a gravitational wave detection where we also get an electromagnetic signal from the same source,” Key explained. She noted that various wavelengths of light, from gamma ray to radio, require different types of tools to detect and reveal different things about objects observed. Key said gravitational-wave astronomers refer to such science as “electromagnetic astronomy.” The big hope, then, is to learn even more if there can be an electromagnetic observation as well as a gravitational wave observation of the same event.

“That’s what we would call a multimessgenger source,” Key said.

A difficult search

Einstein never thought gravitational waves could be detected because he figured they would be too small. It took a century of technological advances to prove him right—again. Finding a multimessenger source may be an even more elusive needle in the cosmic haystack.

Key explained that, right now, it’s hard for LIGO to detect with precision from whence a source signal originates. When they detect a source they send an alert to about 60 electromagnetic astronomy partners and give them a general direction in which to look. In addition to the challenge of pinpointing the source, they also don’t really know what to look for. Key said their models aren’t very good, not yet anyway. Light from a source may have already passed, but there could be x-rays, gamma rays, afterglow, or shock waves under certain conditions.

Fortunately, LIGO is getting better. The addition of more Earth-based observatories will help better locate sources and discover collisions of neutron stars or stellar-mass black holes. Project LISA, scheduled to launch in 2029, will look for supermassive black hole collisions and “extreme mass ratio in-spirals” which occur when a little star or black hole falls into a big black hole. Pulsar timing arrays could detect when supermassive black holes collide in galaxy mergers. There’s even study of the cosmic microwave background to try to detect gravitational waves from early universe.

“Just like electromagnetic astronomy, different sources are detected by these different kinds of experiments,” Key said. “We need all these different kinds of gravitational-wave experiments to be able to study the gravitational-wave sky.”

The LIGO Scientific Collaboration includes more than a thousand scientists from 15 countries and 90 institutions. Four of the institutions are in Washington: The University of Washington, UW Bothell, Whitman College, and Bellevue College.

Unknown discoveries ahead

Key said it is an interesting time to be involved in the field as LIGO is just into its second observing run.

“We’re really going to be able to map out and explore the population of black holes in our universe,” Key said.

“We don’t know what we’ll discover, and that is always the story of a new astronomy,” she added. ”We do not know very much about black holes in general, and so this is a new way to study the universe and study what is out there. It will be very exciting!”

LIGO could discover new kinds of sources like cosmic strings, study supernovae, and maybe even lead to the detection of dark matter and dark energy.

“We are lucky we live in the era of gravitational-wave astronomy, and we hope soon that it will be the era of multimessenger astronomy,” Key concluded.


Solstice sunset watch and LIGO info on our calendar this week

The calendar year is winding down, and astronomy clubs are hustling to get a last few events in before we plunge into 2017.

Rose City AstronomersThe Rose City Astronomers eschew their usual formal meeting for their annual holiday potluck at 6:30 p.m. Monday, December 19 at the OMSI auditorium in Portland. Leftovers from the event have traditionally been donated to a homeless shelter, and this year the astronomers are also collecting warm clothing for donations, figuring that astronomy folk may have a supply of such to bring comfort to those late-night sessions at the eyepiece.

The Eastside Astronomical Society will hold its monthly meeting at 7 p.m. Tuesday, December 20 at the Lake Hills Library in Bellevue. NASA Solar System Ambassador John McLaren will give a talk about the history of scientific exploration of the Sun, and look ahead to future efforts to learn even more about our nearest star.

Seattle Astronomical SocietyThe Seattle Astronomical Society will hold its monthly meeting at 7:30 p.m. Wednesday, December 21 in room A102 of the Physics/Astronomy building on the University of Washington campus in Seattle. Joey Key, a professor at the University of Washington-Bothell, will talk about the next LIGO run searching for gravitational waves, which will also involve astronomical collaboration is search of an elusive “multimessenger source,” a signal that could be detected both in gravitational waves and electromagnetic radiation. Interesting stuff!


VMMEPPThe Viking Mars Missions Education and Preservation Project plans an informal information session for 4 p.m. Tuesday, December 20 at the Hillsdale Library in Portland. This family-friendly event will feature artifacts from the Viking mission, activities for kids, and lots of information about Viking history. Check out our recent article and podcast about the project. The year end is a good time to lend a little financial support to this great history project, too!

Solstice sunset watch

Join Alice Enevoldsen of Alice’s Astro Info and watch the first sunset of winter at 3:45 p.m. Wednesday, December 20 at Solstice Park in West Seattle. The solstice is at 2:44 a.m. PST on Wednesday. Sunset that evening is officially listed as 4:20 p.m., but Enevoldsen says they’ve noted that it’s typically about ten minutes early because of the horizon at that spot. She gives a fun and informative presentation about the mechanics of the seasons, and is persistent about it—this will be her thirty-first seasonal sunset watch. That’s a lot of solstices and equinoxes! Come by even if it’s cloudy, because the Sun sometimes sneaks through anyway, but driving rain makes it a no-go.

Futures file

You can scout out future astronomy events on our calendar. The page also features a full schedule of planetarium and stage science shows at Pacific Science Center.

Up in the sky

The Ursid meteor shower peaks this week. This Week’s Sky at a Glance from Sky & Telescope magazine and The Sky This Week from Astronomy offer more observing highlights for the week.


Dava Sobel talk highlights week’s calendar

A talk by author Dava Sobel is the highlight of this week’s astronomy calendar. Sobel, whose new book is The Glass Universe: How the Ladies of the Harvard Observatory Took the Measure of the Stars (Viking, 2016) will speak at 7:30 p.m. Thursday, December 15 at Town Hall Seattle.

The book is the story of the contributions of women at the observatory who made major advancements in the science, often without getting proper credit or recognition. From Williamina Fleming, originally hired as a maid, who identified ten novae and more than three hundred variable stars to Dr. Cecilia Helena Payne-Gaposchkin, appointed as the first woman professor of astronomy at Harvard in 1956, this group of remarkable women disproved the notion that “the gentler sex” had little to contribute to human knowledge.

Tickets to Sobel’s talk are $5 and are available online.

Astronomy on Tap Seattle

December’s edition of Astronomoy on Tap Seattle will consist of three shows at the University of Washington Planetarium on Wednesday, December 14. The program will be a guided tour of the universe. Unfortunately, all of the seats for the three shows were snapped up quickly, but you might watch the AoT Facebook event page to see if any openings occur.

Public night in Pierce County

The Tacoma Astronomical Society plans one of its public nights for 7:30 p.m. Saturday, December 17 at the Fort Steilacoom campus of Pierce College. The indoor program will be a viewing of a movie about the Christmas star. If the weather is clear they’ll break out the telescopes for some observing, too.

Futures file

You can scout out future astronomy events on our calendar. The page also features a full schedule of planetarium and stage science shows at Pacific Science Center. Recently added events include:

Up in the sky

The Geminid meteor shower peaks this week, but will have to compete with the full Moon. The Sky This Week from Astronomy magazine and This Week’s Sky at a Glance from Sky & Telescope offer more observing highlights for the week.