Category Archives: astronomy

Finding life

A trio of scientists from the University of Washington took the audience on a search for life on other planets during a recent Science in the City talk at Pacific Science Center.

Professor Erika Harnett opened the evening explaining the overall work of NASA’s Virtual Planetary Laboratory, which is headquartered at the UW.


Erika Harnett (Photo: Greg Scheiderer)

“We use a variety of techniques to study planets found in our solar system and in other solar systems for their potential habitability, the potential for life developing there,” Harnett explained.

Harnett’s particular research interest is on the vanishing atmosphere of Mars. Rovers there have helped us confirm that, while the Red Planet is now cold and arid, it was once warm and had oceans and flowing rivers. It also once had a global magnetic field, but it doesn’t any more.

“At some point in Mars’s history—and we’re really having a hard time telling when—its global magnetic field disappeared, and at that point its atmosphere was fully exposed to the radiation of space,” Harnett said. “Probably at that point it started losing a large amount of its atmosphere to space and that’s when water stopped becoming stable.”

There’s lots of ice at the poles and underground on Mars, but if warmed it would go straight to vapor because of the low atmospheric pressure.

Harnett and others are working to figure out the time line for if and when Mars was habitable.

Space is big

While we’ve been to Mars robotically and may well go in person one day, Harnett noted that space is big and there aren’t that many other places to go where life might be possible. For the rest of the universe we use remote sensing.

“We train telescopes looking at a variety of wavelenghts at those locations and try to see what kind of information we can read from those wavelengths of light,” she said.

We can figure out a lot even from a little bit of light. Aliens looking at Earth from afar might conclude that the blue light means lots of water. They could measure our rotation by tracking light changes. Green or brown light might mean vegetation while white would be an indicator of ice. We could use similar methods learn such things about exoplanets far away.

Life on Jupiter’s moons

Marshall “Moosh” Styczinski is a UW graduate student who said he first got interested in Jupiter after watching the movie 2001: A Space Odyssey. Jupiter is still his favorite planet.


Moosh Styczinski (Photo: Greg Scheiderer)

“Its got these four big moons that are a great place to start looking if we want to find life elsewhere in the solar system,” Styczinski said. The focus is on Europa, but the other Galilean moons play a part as well.

“Io plays a surprisingly big role in both why Europa is a promising place to look, and how we study it,” Styczinski noted. Io is pockmarked with volcanoes and its surface is coated with sulfur spewed from those volcanoes. The moons are heated internally because of tidal heating and orbital heating, and not just on the rocky moons.

“Tidal heating causes friction in the interior that warms up the rocks and melts the ice from the underside,” Styczinski explained. “The ice forms a thick crust on top that acts like a blanket, keeping the water warm from the cold space outside.”

Life needs more than just water. Europa also probably has nutrients because liquid water comes into contact with hot rocks.

“Hydrothermal vents are what makes Europa an exciting place to look for life,” Styczinski said. “It has all the basic ingredients that life needs: an energy source, nutrients, water, and shelter.”

We’ve learned a lot about Europa and made models based on our observations so far, but we need more data to get a better handle on questions like the inner structure of this moon, how deep the water is, and where geysers and hydrothermal vents might be found. The Galileo probe is no more, but a couple of other missions are on the drawing boards. NASA plans to launch the Europa Clipper some time in the next decade, and the European Space Agency is scheduled to launch JUICE—Jupiter Icy Moons Explorer—in 2022.

“Both of these missions are going to visit Europa many times, and return lots of valuable measurements that can help refine our models,” Styczinski said. “Finding the right model for Europa’s interior can directly guide future missions by telling them where to go and what we might find when we get there.”

Analyzing exoplanets

We know for certain of some 2,500 exoplanets—planets orbiting stars other than our own Sun—and there are about five thousand more possibles, of which UW grad student Brett Morris, a co-founder of Astronomy on Tap Seattle, expects about 95 percent will also be confirmed as planets. Most of these have been discovered by the Kepler telescope observing a dip in the light when an exoplanet transits in front of its host star. Morris said this discovery is not really so tricky as it sounds.


Brett Morris (Photo: Greg Scheiderer)

“Probably even your iPhone camera is good enough to measure the change in brightness of the Sun when something goes in front of it,” he said. “If you just measure the brightness of the star instead of actually resolving the surface and seeing things going on, you can discover planets.”

Morris said that for every exoplanet the size of Jupiter, they’re discovering two that are about the size of Neptune and a dozen that are roughly the size of Earth.

“The big suprise is that the most common type of world is one that we don’t know anything about,” Morris said. A great many exoplanets have been discovered that are somewhere between the size of Earth and Neptune, which is about four times the diameter of the home planet. Since we don’t have any of these “mystery worlds” of that size in our solar system, the first thing astronomers want to figure out is at what size point these planets are more likely to be gaseous than rocky.

“Exactly where that line is will determine how much habitable real estate there is in the universe,” Morris said, as we don’t expect anyone or anything to be living on gas planets.

Morris is looking forward to the launch of the James Webb Space Telescope, now scheduled for next year. JWST will see in infrared, and will examine spectra of light from the atmospheres of exoplanets to reveal the elements that exist there.

“What we hope to look for are oddballs,” Morris said. Earth, for example, is the oddball of our solar system. While Venus and Mars have atmospheres of mainly carbon dioxide, ours is rich with nitrogen, oxygen, and a host of trace elements.

“Life is what causes the atmosphere here to be different,” Morris said. “We might have trouble saying whether or not life is to blame if we were looking at planetts in other solar systems, but we could definitely flag that one and then try to study it harder, because something interesting is going on there.”

After the talks we watched the 3-D movie The Search for Life in Space. The film is visually spectacular. One often had the notion that a moon or the Cassini spacecraft were about to land in the next seat. It’s worth a look if you get a chance. It’s showing at Pacific Science Center at least through January. Check out the trailer below.



Gift ideas for the astronomically inclined

It’s that time of year again when we start getting questions about what sorts of gifts to give to astronomy buffs. Here are a few great ideas for you.

Year of the eclipse

Eclipse map 2024

Map courtesy Michael Zeiler,

A solar eclipse was visible all over the country back in August, and the path of totality stretched from coast to coast in the United States. Eclipse mementos would make excellent gifts this year. A great source for them is, which has a wide selection of eclipse maps, attire, and accessories, and is running discounts this month. Plus it’s never too early to start gearing up for 2024’s eclipse! We interviewed mapmaker Michael Zeiler late last year about his work; check out the article and podcast based on that interview. Zeiler’s maps are gorgeous and suitable for framing.

Sorin Space Art out of Denver offers some marvelous items, including prints of Sorin’s solar eclipse photography. He’s also made some hand-painted tree ornaments depicting the Moon, Sun, and planets, but as of this writing he was running a bit short of supply on those. Sorin also is the proprietor of Astro Box, a quarterly subscription service that delivers space art, writing, apparel, and more four times each year. It’s a cool gift that keeps on giving.

Two Chicks Conspiracy offers a line of artistic belts and accessories. Several of their belts have space-themed designs, and they created a special key fob in commemoration of the 2017 total solar eclipse.


Tyler Nordgren’s book Sun Moon Earth: The History of Solar Eclipses from Omens of Doom to Einstein and Exoplanets (Basic Books, 2016) was on our year-end gift list last year and remains a good pick this time around. It’s a combination of eclipse mythology and history, travelogue, and eclipse science, and is a fine read. Check out our review of the book and our recap of Nordgren’s author talk about it.

Another good read for eclipse year is David Baron’s American Eclipse: A Nation’s Epic Race to Catch the Shadow of the Moon and Win the Glory of the World (Liveright, 2017). Baron’s book is a look back at the American total solar eclipse of 1878 and in particular how main characters Thomas Edison, Maria Mitchell, and James Craig Watson led high-profile eclipse-viewing expeditions to the wild west that helped spark a national interest in science. Baron gave a talk about the book earlier this year. Here’s our recap.

Ethan Siegel‘s book Treknology: The Science of Star Trek from Tricorders to Warp Drive (Voyageur Press, 2017) will please anyone who has been a fan of any of the Star Trek television shows or movies. Check our article and podcast with Siegel about Treknology.


Recommending a gift telescope is tricky business. I’ve written a number of past articles on the topic, and the ideas there still hold true. If you don’t know what to get, a great reference is the Backyard Astronomer’s Guide (Firefly Books, 2008) by Terence Dickinson and Alan Dyer. It’s a marvelous book for walking one through the ‘scope-choosing process, based on one’s astronomical interests. I used it when I first started out in stargazing, and it’s still a valued reference years later.

If you want to get a first-hand look at a variety of different telescopes, including solar scopes that are designed for observing the Sun, it would be worth a trip to Cloud Break Optics in Ballard. They have quite a selection of ‘scopes in their show room and a lot of experience in stargazing and astrophotography. They’re also running a holiday blowout sale on both new and used gear. Cloud Break Optics is a patron of Seattle Astronomy on Patreon.

That said, I will let you know that the Orion eight-inch Dobsonian telescope is my personal scope of choice. It’s easy to use—just take it out to the back yard, point at something, and take a look! With its simple design it also delivers the most visual bang for the telescope buck. This telescope is really not for photography, though I’ve used it to get smartphone pictures of the Moon and the Sun. Other objects like galaxies or nebulae require longer exposures and that means a ‘scope that can track objects to compensate for the Earth’s rotation. That starts to run into a little money.

Binoculars are also a good gift for someone just starting out in astronomy. Get some that are at least 10x power and 50mm in aperture. I have a 10×50 outfit from Orion, and one can see a lot of neat stuff with a good set of binoculars.


If you’d rather give experiences than stuff, how about a membership to a local organization? The Pacific Science Center, the Museum of Flight, and the Oregon Museum of Science and Industry often have space- and astronomy-themed exhibits and presentations. Memberships are a good value that keep on giving all year long!

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Calendar: Club meetings and planetarium shows this week

We have two astronomy club meetings and a handful of planetarium shows on the calendar for the coming week.

Science Fact or Science Fiction?The Pierce College Science Dome will offer a special program, Science Fact or Science Fiction, from 5 p.m until 8 p.m Friday, December 1. The evening will include lots of hands-on activities as well as a planetarium show that compares fictional planets to some real ones we’ve discovered.

It’s all free, but early reservations are recommended for the planetarium shows. Do that online.

Saturday, December 2 will be a busy day at the dome. It’s new planetarium show for children, Amazing Aurora, will run at 12:30 p.m. and 2 p.m. each Saturday during December. Following this Saturday at 3:15 p.m. they’ll run the all-ages show “Life: A Cosmic Story.” They’ll present a different all ages show each Friday and Saturday during the month.

Get in some Cosmic Yoga at 7 p.m. this Friday, December 1 at the WSU Planetarium in Pullman. The event includes live music, a yoga instructor, and outstanding astronomical images. Cost is $15, check or cash at the door. Then on Sunday, December 3 at 5 p.m. the planetarium show “Some Like It Hot” will look at temperature in the universe, from the cryogenic outer reaches to the stellar nuclear furnaces.

Celebrate Mars!

Red Planet Day at PacSciTuesday, November 28 is Red Planet Day at the Pacific Science Center. Wear a red article of clothing to receive half-off admission.

Activities include a special planetarium show Mars Live! that explores the history of Mars exploration and the geology and the future of the Red Planet. Catch a Mars presentation on Science On a Sphere and enjoy hands-on activities relating to the alien planet. While you’re there you might check out the IMAX® documentary, The Search for Life in Space to explore the age old question: “Are we alone?”

Club meetings

Rose City Astronomers in Portland will hold their monthly meeting at OMSI at 7:30 p.m. Monday, November 27. OMSI’s Jim Todd will give a behind-the-scenes tour of the newly remodeled and updated OMSI Planetarium.

The Spokane Astronomical Society plans its monthly meeting for 7:30 p.m. Friday, December 1 at the planetarium at Spokane Falls Community College.

The Tacoma Astronomical Society will hold one of its public nights at 7:30  p.m. Saturday, December 2 at the Fort Steilacoom campus of Pierce College. The indoor program will be about choosing a gift telescope. If the weather cooperates, they’ll break out the telescopes for some observing.


Merging neutron stars and cool galaxies at Astronomy on Tap Seattle

One of the cool things about the Astronomy on Tap Seattle series of talks in pubs is access to scientists who are working on headline news. It happened at their October gathering at Peddler Brewing Company in Ballard. Jennifer Sobeck, a stellar astrophysicist in the Department of Astronomy at the University of Washington, was all set to give a talk titled, “A Hitchhiker’s Guide to the Galaxy: Bumming Around the Milky Way.” But a few days before the talk the news hit that LIGO and others had detected gravitational waves generated by merging neutron stars. Neutron stars are Sobeck’s thing, so the script went out the window and we learned about what happened.

Sobeck noted that neutron stars are what’s left behind when high-mass stars—around four to eight times the mass of the Sun—blow up in a supernova. Neutron stars are incredibly dense; the mass of the Sun packed into something 12 miles across. They have a crust, though light still gets through.

“Inside is just basically a soup,” Sobeck said. “It’s a hot mess.”

Everything inside is so compressed that scientists call it “degenerate.”

“There are no more atoms, there are no more molecules, those are all blown apart,” Sobeck explained. “It’s just like a soup of neutrons; there are just tons of neutrons, and the really cool thing is down in the center, they think the pressures are so high that you actually might get quarks.”

Neutron star merger animation by ESO/L. Calçada. Music: Johan B. Monell

August discovery

Scientists knew they had detected a neutron star merger rather than the sort of black-hole mergers previously spotted by LIGO because the signals are different. The interesting thing about the detection of two neutron stars merging is that we could see it visually because the event created a kilonova, like a supernova, but smaller.

“It’s a little bit less on the explosion scale,” Sobeck said. “Kilonova means that you’re able to have electromagnetic radiation across the spectrum that a whole bunch of facilites were able to monitor.”

So when LIGO and VIRGO detected the gravitational wave, with the help of the Fermi gamma ray space telescope and the ESA’s Integral gamma-ray observatory they they were able to narrow down the location of the event and tell others to look there. When the optical observations came in, the kilanova was spotted in the galaxy NGC 4993.

“This has never been done before,” Sobeck noted. The detection occurred in mid-August of this year, and by the end of the month the visual was gone.

“This kilonova explostion lasted only for a period of only 15 days,” Sobeck said.

Observations were made not just in the visual, but across the spectrum from gamma rays to radio, and more than a dozen observatories were involved in the analysis.

“You’re getting a different piece of information from all of these parts of the spectrum,” Sobeck noted. “They all helped fill in that puzzle.”

The story in the media

Where stuff comes from

Periodic table showing origin of elements in the Solar System, by CMGLee on Wikimedia Commons based on data by Jennifer Johnson, Ohio State University.

Sobeck said the press went a little overboard with headlines such as collision “creates gold” (CNN)  and “Universe-shaking announcement” (New York Times), yet it’s true that the kilonova made some gold. Sobeck showed the periodic table of elements at left (click to see it bigger), modified to show where all of the elements came from. She noted that hydrogen, helium, and a bit of lithium came from the Big Bang, the rest were made in stars. But stars can only fuse elements as heavy as iron. To get the really heavy stuff called lanthanides you need a kilanova. The emitted light tells you what’s there. If you see blue light after a kilonova, that means there’s a high concentration of silver, cadmium, and tin. If the light is more red, then platinum, gold, mercury, or lead is present.

“This particular event went from blue very, very, quickly to red, and it stayed red most of the time,” Sobeck said. “Hence, we’ve got a bunch of gold on our hands.”

“We found out that neutron-star mergers do make elements,” she said. “We were right, so huzzah!”

All kinds of galaxies

Grace Telford, a graduate student studying astronomy and data science at the UW, stuck with her original topic of “A Whirlwind Tour of Galaxies: the Tiny, the Gigantic, and Everything in Between” for the October Astronomy on Tap. She noted that there are several ways to classify galaxies:

  • Stellar mass or brightness
  • Shape
  • Star formation rate
  • Nuclear activity

Stellar mass or brightness

This is pretty straightforward.

“Basically the more stars a galaxy has, the brighter it is,” Telford noted. There’s quite a range of sizes. The Milky Way is a pretty common-sized galaxy, and it’s hard to make them bigger. The largest are around 10 times the size of the Milky Way.” Smaller galaxies are plentiful.

“A dwarf galaxy is something that is at least a hundred times less massive than our Milky Way,” Telford said, and they can go a lot smaller.

Way out at the small end of the chart are ultra faint dwarf galaxies, which can’t really be seen because they’re too faint. They can’t be detected at long distances.

A recently discovered type is called an ultra diffuse galaxy. This may be the same size as the Milky Way but have 100 times fewer stars, all held together by dark matter.

“This is an open area of research,” Telford said. “It’s hard to explain how to form these wierdo galaxies that are not very massive at all, but huge.”


The three main shapes of galaxies are elliptical, spiral, and irregular. Spirals may come with a large central bulge or a bar. Irregular galaxies tend to be small.

Star formation rate

It’s in star formation rate that galaxies really differentiate themselves, Telford said. Galaxies that emit a lot of blue light have lots of young stars and new star formation. Galaxies that look red are “quenched.” Their stars are older, and there’s little new star formation.

In between red and blue is the “green valley” of galaxies. They don’t actually emit green light, but they’re in transition from blue to red.

An interesting type is the “starburst” galaxy. These are galaxies that somehow stumble into a source of gas that wasn’t available to them before.

“They have the ability to form stars at a very high rate relative to the normal amount of star formation for a galaxy of its size,” Telford explained. “As a result, you have a lot of these massive young stars that are dying and exploding as supernovae and injecting a lot of energy into the gas.”

These objects are short-lived, they exhaust their gas in a hurry, at least in astronomical terms—in between 100 million years and a billion years.

Nuclear activity

Most galaxies have supermassive black holes, which can create jets of energy.

“Sometimes these black holes eat a lot of gas really quickly and then they blow out a whole bunch of energy,” Telford explained. These jets are nuclear activity. Galaxies with active galactic nuclei are most typically found in the green valley, though they’re in other types as well.

Telford gave a plug for Galaxy Zoo, where you can go looking for these differing types of galaxies and actually participate in citizen science.


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Visiting Vesta and Ceres

The Dawn spacecraft has found a lot of surprises at Vesta and Ceres. Debra Buczkowski
a geologist and planetary scientist at the Johns Hopkins University Applied Physics Lab, gave a talk recently at the Museum of Flight discussing some of the findings from the mission.


Dr. Debra Buczkowski, a geologist and planetary scientist at the Johns Hopkins University Applied Physics Lab, spoke about the findings of the Dawn mission to Vesta and Ceres recently at the Museum of Flight. (Photo: Greg Scheiderer)

Vesta was Dawn’s first stop, entering orbit around the asteroid on July 15, 2011. Scientists expected to find volcanoes on Vesta. Buczkowski explained that this expectation traces back to meteorites found on Earth that are know to be from Vesta. These are known as HEDs: “howardite–eucrite–diogenite.” These closely resemble igneous rocks found on Earth, and those are made from volcanic activity. But the volcanoes aren’t there.

Before Dawn arrived at Vesta the Hubble Space Telescope showed that Vesta wasn’t spherical, but rather was significantly flattened out at its south pole. Scientists speculated that this was because of an enormous impact, and that proved to be correct. Dawn observed a huge impact crater, now called Rheasilvia Basin, the rim of which is almost as wide as Vesta itself.

“It really should have broken the asteroid apart,” Buczkowski said of the impact that created the basin, which has a huge central peak. Dawn also found a second impact crater, Veneneia Basin, which is almost as large.

Another surprise finding from Dawn is that Vesta is fully differentiated.

“Most of the asteroids are just kind of chunks of rock with one kind of rock all the way through,” Buczkowski explained. “Not Vesta; Vesta actually has a core, it has a mantle, and it has a crust.”

Vesta’s core is about half the diameter of the asteroid itself, about 220 kilometers.

“This is probably why Vesta did not fall apart when the Rheasilvia Basin formed, because it has this huge, massive core,” Buczkowski said.

The surface of Vesta was found to have lots of fractures, features larger that Earth’s Grand Canyon that look like faults. Buczkowski said they did a lot of computer modeling to see if an object the size of Vesta with a core the size of Vesta’s could develop fractures on the crust.

“The stresses that result from that huge impact kind of get redistributed because of the giant core,” she said of the findings. “Instead of being focused around the crater, they move to the equator and fracture at the equator. If we do this same model without the giant core, there’s no fracturing at the equator. So it’s because of the giant core that we have these huge fractures.”

Buczkowski said that was a little disappointing because they were hoping for volcanoes or magma-driven geology. While they didn’t find volcanoes, there is evidence of moving magma that didn’t break through to the surface. Rather, it pushed some of the surface upward, forming mounds.

On to Ceres

Dawn departed Vesta in September 2012 after spending about 14 months in orbit. As Dawn approached the dwarf planet Ceres there was much speculation about extremely bright spots on its surface that were found in Hubble images. Other observations had detected water vapor on Ceres. Since Ceres is relatively large but not dense, scientists were expecting to find ice. But there was more rock and less ice than anticipated. What they did find, Buczkowski said, was evidence of volcanism.

Occator crater

This image from NASA’s Dawn spacecraft shows Occator Crater on Ceres, with its signature bright areas. Dawn scientists have found that the central bright spot, which harbors the brightest material on Ceres, contains a variety of salts. (Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)

“We’re not expecting magma on Ceres,” she said. “Ceres isn’t dense enough for the kind of magma that we’re used to here on Earth, made out of silicate rocks. This is something called cryomagma; it is basically ice with a little bit of rock.”

The biggest and brightest of the bright spots, named Cerealia Facula, is in the crater Occator. Many of the craters on Ceres are fractured, even on the crater floors, and the many bright spots on Ceres are associated with these fractures.

“What it’s looking like is that we’re having cryomagmatic activity underneath (Occator) crater,” Buczkowski said, “and what’s coming up out of these fractures is a pyroclastic spray, and the water, the volatiles in that, is sublimating away and all it’s leaving is the sodium carbonates.” Those are the bright spots we see all over Ceres.

Dawn also found that Ceres is covered in ammoniated phyllosilicates.

“Ammonia is interesting,” Buczkowski explained. “We don’t expect to find ammonia this close to the Sun, it’s usually something that’s found further out in thhe solar system.” They’re still studying whether Ceres may have formed further from the Sun and migrated in, or if the ammonia somehow made its way to Ceres from the outer solar system.

It turns out that Ceres had quite a few volcanoes, though most of them have now collapsed. There’s one that hasn’t, known as Ahuna Mons, that stands about five kilometers tall. It’s a cryovolcano.

“The volcano that we thought would be on Vesta is on Ceres,” Buczkowski noted. Ahuna Mons may be younger than the others, and also may collapse over time.

Like Vesta, Ceres was found to be differentiated, though only partially so.

“There’s a rocky core, there’s a volatile-rich mantle, and there’s a muddy slurry, a mud ocean” below the crust, Buczkowski said.

Dawn at Ceres and VestaCeres is now considered a dwarf planet, while Vesta still has asteroid status because of its lopsided shape from the giant impact. Buczkowski figures Vesta deserves dwarf-planet status, too. Whatever you call them, she thinks they’re fascinating to study because they’re kind of a bridge between the asteroids and rocky planets.

“These are more involved bodies than just plain, old asteroids,” Buczkowski said. “They’re not just chunks of rock floating in space. They’re actually like little mini-planets. They’ve got a lot of planet-like properties.”

Though they’re pretty small, they can teach us a lot.

“They’re interesting to us because they tell us a lot about how Earth and the other planets formed,” Buczkowski said. “Studying these little protoplanets we actually are looking back to the beginning of the solar system.”


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APOD: more than just pretty pictures

The Astronomy Picture of the Day is more than just a pretty photo. In fact, each of the featured images may well have more than a thousand words packed into it. You just need to drill down deeper into the site.

John McLaren, a NASA Solar System Ambassador and treasurer of the Seattle Astronomical Society, gave a presentation about APOD at the society’s meeting last week. He said the key to finding a wealth of information about celestial objects is dragging your eyes away from the pretty pictures long enough to notice the explanation of the photo and, more importantly, the submenu below it. McLaren uses this information when preparing presentations about astronomy for various groups.

“You can build a more complete story,” he explained. “There are good links here for education, for outreach, and home-schooling groups.”

You’ve probably noticed that the explanations of the photos use plenty of links to further information. Below the explanation there’s typically a set of “more on” links about objects or content. The real prize, though is in the index, a fully searchable listing of what’s on the APOD site.

That’s a lot of stuff. McLaren noted that the site was started by Robert Nemiroff and Jerry Bonnell when both worked at the Goddard Space Flight Center. The first posts were in June of 1995, and there have been more than eight thousand of them since. McLaren pointed out that when you look at the site, it is very 1995. There’s no flash or fancy moving menus. It’s pretty straight HTML, and the authors figured that changing things would run the risk of breaking a zillion links to APOD information.

Earth from Apollo 17

The Earth from Apollo 17
Picture Credit: NASA, Apollo 17, NSSDC

They don’t update the photos published, either. Clicking on each photo gives you the best version of it that they have. The one at left, a photo of Earth taken from Apollo 17 in 1972, was posted in the first week of APOD’s operation. When McLaren showed this photo on the big screen during his presentation, there was some laughter about its low resolution. He reminded us that in 1995 we were probably dialing in to the Internet with a 2400 baud modem, and that wouldn’t deliver the high-res goods in the manner to which we’ve become accustomed in our broadband world.

Click the “archive” link on each page and you’ll find a long scroll, day by day, of every APOD ever. The “index” link takes you to a menu of stars, galaxies, and nebulae, solar system objects, space technology, people, and the sky. Clicking on these will give you a handful of “editors’ choice” photos they consider to be the most educational on the chosen subject.

McLaren found this photo, the APOD of October 20, 2002, of the space shuttle docked with the Russian Mir space station in 1995. It made him wonder who took it. Was it the first known selfie?

Shuttle and Mir

The Space Shuttle Docked with Mir. Credit: Nikolai Budarin, Russian Space Research Institute, NASA

“Since it was the first docking, they wanted to get good information about how the two spacecraft functioned together,” McLaren explained. “So one of the Soyuz crews on Mir actually undocked their Soyuz spacecraft, did a fly-around, and observed the combination.” All of that was found by following the links on the photo page.

Astrophotographers who aspire to be published on APOD may well wish to check out its index of Messier objects. McLaren points out that many of the objects in the index are represented by numbers, not pictures.

“They don’t have photos of all the Messier objects posted yet, so if you submit a good color picture of them you may get your photo as the astronomy photo of the day,” he noted, which could lead to fame and fortune or at least bragging rights.

The search engine for the index is useful. Type in “Saturn rings” and it will find 200 items.

“There’s a wealth of information in there if you’re looking for something,” McLaren said.

So the next time you’re checking out the Astronomy Picture of the Day, remember that there’s a whole lot of knowledge lurking beneath those gorgeous photos.


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Seeing the invisible and finding aliens using polarimetry

The topic line for last week’s gathering of Astronomy on Tap Seattle was What the Hell is Polarimetry?, and it seemed that a significant portion of the audience at Peddler Brewing Company in Ballard shared the question.

UW postdocs Jamie Lomax and Kim Bott explained that when light starts from its source the oscillation of its wave—its “wiggle”—goes in all directions until an interaction with something makes it polarized.

“That just means that it’s wiggling in one direction,” Lomax noted. “There’s a preferred plane for that wiggle to happen in, and in polarimetry what we’re doing is measuring that preferred plane and we’re looking for light that has been polarized.”

“It can help you figure out the shape of things without having to resolve the object,” Bott added.

Polarimetry and massive stars

Lomax studies massive stars and has found use for polarimetry in her work. She gave a talk titled, “Seeing Invisible Circumstellar Structures.”

Jamie Lomax

Jamie Lomax

“The holy grail for us in massive star research is to be able to take a massive star at the beginning of its lifetime, figure out how massive it is,” Lomax said, “and map out what its life is going to look like and figure out what supernova it’s going to end its life as.”

“It turns out that is really hard, and it’s complicated by the fact that most massive stars are probably in binary systems,” she added. Since about two-thirds of massive stars are part of a binary system, one might expect that two-thirds of core-collapse supernovae would be from such systems.

“There’s a problem, and that is we’ve only seen maybe two or three core-collapse supernovae where we have evidence that suggests that it’s come from a binary star,” Lomax said.

Part of the problem, she said, is that we don’t yet know enough about the evolution of binary star systems.

“We can try to hammer out the details of how that mass is transferring between the two stars and when the system is losing material to try to figure out how that effects its future evolution,” Lomax said. “Once we start answering questions like that we can start to tease out why we aren’t seeing all of these binary supernovae we think we should be seeing.”

Lomax talked about the star Beta Lyrae, a binary system. The primary star in the system is losing mass that gets gobbled up by the secondary. This transfer of mass also forms a thick accretion disk of gas around the secondary—so thick light from the actual star can’t get through. There’s also evidence that there are jets shooting out of the system, but we don’t know where they are.

“These are all features that we can’t see very well,” Lomax said. “We can’t see the mass transfer stream between the two stars, we can’t see the jets.”

Here’s where polarimetry comes in. If a star is surrounded by a cloud of gas or dust that is circularly symmetrical, when the starlight interacts with that material the light becomes polarized, and the wiggles line up tangentially with the edge of the disk. If the cloud is elongated in some way, the wiggles form in a “preferred” direction.

“That preferred wiggle direction is 90 degrees from the direction of the elongation of the disk, so you can back out geometric information pretty quickly,” Lomax said. “Just by looking at how the light is wiggling I can tell you how the disc is oriented on the sky.”

Lomax figures that if you don’t do polarimetry you’re throwing out free information.

“You can see invisible things—to you—and that gives you extra information about what’s going on in different systems.”

Exoplanets and aliens

Bott’s talk was titled “The Polarizing Topics of Aliens and Habitable Planets.” She studies exoplanets and said polarimetry comes in handy.

“Stars don’t produce polarized light, which is really great if you’re trying to look at something dim like a planet,” she noted. The polarimeter will simply block out the starlight. There are then a number of things that might be spotted on the planet:

  • Glint from an ocean
  • Rayleigh scattering
  • Clouds and hazes
  • Rainbows
  • Biosignatures of gases in an atmosphere
  • Chiromolecules
Kim Bott

Kim Bott

These can help astronomers characterize a planet, judge its potential habitability, and even determine if life might already be flourishing there.

Bott said that polarimeters that are sensitive enough to study planets are a recent advance, and they’re studying big, bright planets to get the hang of it. Looking for rainbows can be revealing about liquids in the atmosphere of a planet.

“The light will bend in the droplets at a slightly different angle depending what the droplet is made out of,” Bott said, so they can tell whether its water, methane, or sulfuric acid.

“We’re trying to create these really robust models that will take into consideration polarized light from Rayleigh scattering in the atmosphere as well as from rainbows,” Bott said, “and if you have a planet where you can see the surface you’d be able to see the signature from glint as well.”

Since different substances bend light at different angles, we can also learn a lot by watching closely as planets move through their phases as they orbit their host stars.

“On Earth we have light going from air and bouncing off of H2O water,” Bott said. “That’s going to produce a maximum in polarized light at a different angle than on, say, Titan, where you have light going from a methane atmosphere and then bouncing off of a hydrocarbon ocean.”

“We can actually, in theory, tell what the ocean and atmosphere are made out of by looking at where, exactly, in the orbit we see this glint,” Bott explained.

As for aliens, life requires more complex molecules, chiromolecules, that are “wound” in a certain direction, like our own DNA. Such molecules would produce circularly polarized light, which if detected could be a sign that such molecules exist on the planet.

Astronomy on Tap Seattle is organized by graduate students in astronomy at the University of Washington. It’s next gathering is scheduled for October 30 at Peddler Brewing Company in Ballard.


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