Category Archives: astronomy

The expanding universe: discovery, controversies, and hope

We’ve known that there is a universe outside the Milky Way, and that it is expanding, for less than a century.

“Throughout the entire history of the universe, of knowing it’s expanding, there have been a tremendous number of controversies over it, and there’s still one that persists today,” said astrophysicist and author Ethan Siegel. Siegel, author of Beyond the Galaxy: How Humanity Looked Beyond Our Milky Way and Discovered the Entire Universe (World Scientific Publishing, 2015), spoke at last week’s meeting of the Rose City Astronomers in Portland, Oregon.

The controversy actually goes back to before the expansion was observed, to Albert Einstein. His equations describing general relativity suggested that gravity would collapse the universe onto itself, and as he believed the universe was static, he threw in a “cosmological constant” to push back against gravity. Einstein later called that his biggest blunder, though some wanted to let him off the hook for it when dark energy was proposed to do the exact same thing.

“I am here to tell you that this was Einstein’s reasoning and throwing this in there when he did was a super big blunder because the universe isn’t static,” Siegel said. Einstein should have trusted his theory, he said, and taken it to the next step.

The universe is expanding

By the 1920s Edwin Hubble observed a Cepheid variable star in the Andromeda “nebula” that indicated that it was far outside the Milky Way and a galaxy in its own right. Astronomers were also studying redshift as an indication for the speeds at which galaxies were receding from us. Siegel explained that through this, Hubble determined that the universe was expanding at a rate of 600km/sec/Mpc (kilometers per second per megaparsec.) This became the Hubble constant. But it wasn’t so constant.

Siegel noted that, knowing the size and expansion rate of the universe, you can figure its age by running the numbers in reverse and going back to the beginning, to the Big Bang. The resulting calculation determined that the universe was about two billion years old. Geologists at the time had already pegged the age of the Earth as at least four billion years.

“This was a problem for Hubble, because the universe isn’t allowed to be half the age of the Earth,” Siegel noted. “Either this expansion rate is wrong and this age for the universe is wrong, or the age of the Earth is wrong.”

It turns out that Hubble’s main mistake was in figuring that all variable stars are alike. Siegel said Walter Baade came along in the 1940s and discovered that they are not. Finding that most of the Cepheids Hubble had looked at were non-classical, they re-ran the numbers from Hubble’s data.

“As you accumulate more knowledge, as you accumulate a better understanding of what you’re actually loooking at, you can go back and get more useful science out of this data,” Siegel said. This second look doubled the distance to these stars and reduced the value for the Hubble constant to 270km/sec/Mpc. This in turn put the age of the universe at five billion years.

“That’s better,” Siegel noted. “The universe is older than Earth. That’s one problem solved.”

Narrowing it down

Siegel

Dr. Ethan Siegel, creator of the “Starts With a Bang” blog, gave a talk about the age and size of the universe to the Rose City Astronomers February 20. Photo: Greg Scheiderer.

As time went on astronomers developed the “distance ladder” for determining the vast distances in the universe. You first measured the distance to Cepheid variables within the Milky Way, then gauged the distances to other galaxies using Cepheids spotted there. Type 1a supernovae could be spotted really far out. As we learned more about the stars we got a little better at figuring distances.

Things got really interesting in the 1960s, according to Siegel. We discovered that we could determine the ages of stars by measuring their color and brightness. The Hertzsprung–Russell diagram told us that the oldest stars were between 14 billion and 16 billion years old, significantly older than the age of the universe determined by Baade. Astronomer Allan Sandage, who as a graduate student was an assistant to Hubble, came along and said you needed two things to make the universe that old: it had to be low enough in density to make a vast expansion, and the expansion rate had to be low.

Dueling Hubble constants

This, Siegel said, was where the controversy came in. Sandage said the expansion rate would have to be between 50-60km/sec/Mps. Rival astronomer Gérard de Vaucouleurs of France put it at around 100km/sec/Mpc. The race was on to make observations to see which group was right. Amazingly enough, each group’s observations matched up with what they thought the answer would be.

“This just goes to show that you cannot have the same people making the same measurements and trust them,” Siegel said. “This is why you need independent confirmation.”

It turns out Sandage and de Vaucouleurs were both wrong. There’s still no agreement on the right answer, but the disagreements are getting closer together. Sigel said the Hubble Space Telescope’s improvements in measuring the size of the universe return a value of 74±2km/sec/Mpc. The Planck mission’s observations of the cosmic microwave background radiation suggest 67±1km/sec/Mpc.

“There is a fight over the results like there always seems to be, because we are scientists and we cannot agree on anything,” Siegel said. “That is good, because questioning is what keeps us moving forward and what keeps us learning more.”

“The way we’re going to get there is with more and better data,” he added.

Better data

The better data will come from missions such as the European Space Agency’s Gaia, the James Webb Space Telescope, WFIRST, and the Large Synoptic Survey Telescope, which combined might improve our parallax measurements of cosmic distances by a factor of ten. We might also weed out faulty assumptions in the earlier work or get more accurate insights into the balance between matter and dark energy in the universe.

“If we can wait until the next decade, we might see that 74 number come down, we might also see the 67 number come up,” Siegel said. “The point is uncertainties are going to be reduced by more and better data.”

Siegel said that right now it’s pretty much agreed that the universe is about 13.8 billion years old and consists of about 30 percent matter and 70 percent dark energy. But the miniscule pluses or minuses can lead to huge fights.

“When that data comes in at last we will know exactly how fast our universe is expanding, how old it is, and what it all means for both our cosmic origins and our cosmic fate,” Siegel concluded. “That’s pretty good stuff.”


In the podcast linked below Siegel covers much of the topic matter of this article and his talk. His new book, Treknology: The Science of Star Trek from Tricorders to Warp Drive (Voyageur Press, 2017), is scheduled for release in October.

FacebookTwitterGoogle+EvernoteShare

Search for meaning continues

There is a great menu of interesting talks on this week’s calendar, including three with astronomy themes at a weekend event at Seattle University.

Search for Meaning FestivalSeattle University’s annual Search for Meaning Festival will be held on the university campus all day Saturday, February 25. The festival is a community event dedicated to topics surrounding the human quest for meaning and the characteristics of an ethical and well-lived life. It draws more than 50 authors and artists who will give interactive presentations. Three of these sessions are on astronomy-related topics.

At 9 a.m. Father George Coyne, SJ, former director of the Vatican Observatory and author of Wayfarers in the Cosmos: The Human Quest for Meaning (Crossroad 2002), will discuss the history of the evolution of life in the cosmos. Coyne’s thesis is that this history may lead us to a deeper understanding of what many secular physicists say themselves about the cosmos: that a loving creator stands behind it.

At 10:45 a.m. Margot Lee Shetterly, author of the book Hidden Figures: The American Dream and the Untold Story of the Black Women Mathematicians Who Helped Win the Space Race (William Morrow, 2016), on which the current hit film is based, will give one of the keynote addresses at the festival. Shetterly will talk about race, gender, science, the history of technology, and much else. Reservations for Shetterly’s talk are sold out.

At 12:45 p.m. Marie Benedict, author of The Other Einstein (Sourcebooks Landmark, 2016), will explore the life of Mileva Maric, who was Albert Einstein’s first wife and a physicist herself, and the manner in which personal tragedy inspired Mileva’s possible role in the creation of Einstein’s “miracle year” theories.

Check our post from December previewing the festival, and look at the trailer video below. Tickets to the festival are $12.50 and are available online.

Siegel at Rose City

Author and astrophysicist Ethan Siegel will be the guest speaker at the monthly meeting of the Rose City Astronomers in Portland at 7:30 p.m. Monday, February 20. Siegel will talk about his book Beyond the Galaxy: How Humanity Looked Beyond Our Milky Way and Discovered the Entire Universe (World Scientific Publishing, 2015). He’ll examine the history of the expanding universe and detail, up until the present day, how cutting-edge science looks to determine, once and for all, exactly how the universe has been expanding for the entire history of the cosmos. Siegel is an informative and engaging speaker; check our recap of his talk from last year about gravitational wave astronomy.

AoT Seattle and an app for simulating the universe

AoT FebruaryAstronomy on Tap Seattle’s monthly get-together is set for 7 p.m. Wednesday, February 22 at Peddler Brewing Company in Ballard. Two guest speakers are planned. Dan Dixon, creator of Universe Sandbox² will give an introduction to the app, an accessible space simulator that allows you to ask fantastical what-if questions and see accurate and realistic results in real-time. It merges real-time gravity, climate, collision, and physical interactions to reveal the beauty of our universe and the fragility of our planet. University of Washington professor in astronomy and astrobiology Rory Barnes will talk about “Habitability of Planets in Complicated Systems.” It’s free, except for the beer.

TAS public night

Tacoma Astronomical SocietyThe Tacoma Astronomical Society plans one of its public nights for 7:30 p.m. Saturday, February 25 at the Fort Steilacoom campus of Pierce College. The indoor presentation will be about the zodiac. If the skies are clear they’ll set up the telescopes and take a look at what’s up.

Futures file

You can scout out future astronomy events on our calendar. We’ve recently added several events scheduled at the Museum of Flight, including:

Up in the sky

There will be an annular solar eclipse on Sunday, February 26, but you’ll have to be in South America or Africa to see it. 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.

FacebookTwitterGoogle+EvernoteShare

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.”

FacebookTwitterGoogle+EvernoteShare

Valentine’s week astro events

Astronomy buffs will have to make a tough call Wednesday as two interesting but very different events will be held across town.

CassiniThe Seattle Astronomical Society will hold its monthly meeting at 7:30 p.m. Wednesday, February 15 in room A102 of the Physics/Astronomy building on the University of Washington campus in Seattle. Guest speaker Ron Hobbs, a NASA JPL Solar System Ambassador, will give a talk titled, “Cassini’s Grand Finale: Overview and Challenges.” Hobbs will cover the daring moves the orbiter will make in its final days at Saturn before the mission ends and the craft is crashed into the planet in September.

Women in ScienceMeanwhile at Seattle University the Infinity Box Theatre Project will present its eighth annual Galileo Dialogues at 7 p.m. Wednesday, February 15—Galileo’s birthday!—in the Seattle University Student Union Building, Room 160. The evening is presented in collaboration with the Seattle University Physics Department and the Association for Women in Science, and features a reading by Catherine Kettrick of “Celebrating Women in Science”—things you don’t know about several centuries of women who have made major contributions to several areas of science—mostly in their own words. It’s free, though donations are appreciated. You can reserve a seat online.

Nerds in space

The Science and Math Institute and Multicultural Services at Bellevue College will hold a lunchtime Science Café at 12:30 p.m. Friday, February 17 in room C130 of the student center. Guest speaker Tim Lloyd, a rocket scientist with Blue Origin, will share his experiences working for the local space flight company in a talk titled, “One Nerd’s Journey to Space.”

Planetarium shows

Catch a free planetarium show about New Horizons at the Willard Geer Planetarium at Bellevue College at 6 p.m. or 7 p.m. Saturday, February 18. The shows are sponsored by the college’s Astronomy Department and the Science and Math Institute. There’s no charge, but you can make reservations online to assure yourself a seat.

The Willard Smith Planetarium at Pacific Science Center has programs daily. Find their full schedule on our calendar page.

The Washington State University Planetarium in Pullman offers a show about the Moon on Monday, February 13 and a special Valentine’s show on Tuesday, February 14. Both programs begin at 7 p.m. Admission is $5.

Up in the sky

Have you been enjoying views of Venus lately? The planet reaches “greatest illuminated extent” this week, which means it’s at its very brightest. 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.

FacebookTwitterGoogle+EvernoteShare

Pushing for IDA membership

Kelly Beatty thinks more amateur astronomers should be members of the International Dark-Sky Association (IDA), and he puts his money where his mouth is on the issue. Beatty, a senior editor of Sky & Telescope magazine and a board member of the IDA, made an offer to waive his usual fee for speaking at the recent Seattle Astronomical Society banquet if the group could sign up at least ten new or renewing IDA members. At last word they’d added at least a couple of dozen.

IDA logoStill, Beatty noted at the January 28 banquet that while there are roughly a quarter of a million amateur astronomers in the United States, the IDA has only about 3,000 members.

“That means that roughly one in a hundred amateur astronomers across the U.S. are members of IDA,” Beatty pointed out. “Isn’t that pathetic?”

“What other group has more to gain or lose from the success of the IDA and our dark sky preservation efforts?” he asked.

Beatty

Beatty

Beatty noted that LED street lighting is a major issue, and one on which regular citizens can help. If your city or town hasn’t converted street lights to LED yet, it probably will soon. LED street lights can be cheaper in a couple of ways. They consume less energy than typical street lights (though this paradoxically can cause a municipality to just buy more light), and the fixtures have a longer expected life span. What is important is that cities use fixtures that are at a color temperature of 3,000 kelvins or less. This provides warmer light with less blue in the spectrum. Blue light brightens the night sky more than any other color of light, and exposure to blue light at night has also been shown to harm human health and endanger wildlife.

Beatty said that the city of Phoenix recently decided to install 2,700-kelvin streetlights, Montreal dropped plans to install lights at 4,000 kelvins, and the entire state of Georgia is going with 3,000-kelvin lights.

“You have the power to make a difference in this fight against light pollution, individually and collectively,” Beatty said. “It’s not that people are opposed to doing the right thing, they just don’t know. It’s an education. So if you inject yourself into the process you can and will make a difference.”

IDA’s page about outdoor lighting basics and its LED practical guide have lots of useful information. Oh, and you can sign-up online. There’s a $15 annual membership for students, and standard memberships start at just $35.

FacebookTwitterGoogle+EvernoteShare

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

Pluto

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.”

FacebookTwitterGoogle+EvernoteShare

Astronaut talk, star parties on the week’s calendar

A talk by a visiting astronaut and a handful of public star parties are the highlights of the astronomy event calendar this week.

Barratt

Barratt

The astronaut remembrance exhibit continues all week at the Museum of Flight, with displays and videos honoring the astronauts who have died in the pursuit of space exploration. NASA astronaut Dr. Michael R. Barratt will give a talk at the museum at 2 p.m. Saturday, February 4. Barratt’s appearance is part of the Michael P. Anderson Memorial Aerospace Program, an annual event which gives underserved children throughout Washington the chance to participate in the museum’s educational programs rooted in aerospace. Anderson, a Spokane native, perished in the shuttle Columbia disaster in 2003. Barratt, also a Washingtonian, flew several shuttle and ISS missions and is presently serving in NASA’s International Space Station Operations and Integration branches to handle medical issues and on orbit support. His talk is free with museum admission.

Space infrastructure

Philip Swan of the Atlantis Project will be the featured speaker at Science on Tap at 7 p.m. Monday, January 30 at the Vios restaurant at Ravenna Third Place Bookstore. Swan will give a talk titled, “Space Infrastructure: Ferries are to Bridges as Rockets are to what?”

Planetarium shows

There will be three free public planetarium shows this Friday, February 3 at the University of Washington Planetarium. Showtimes are set for 5:30 p.m., 6:30 p.m., and 7:30 p.m. Tickets are free but they usually go quickly; you can reserve yours online. There are several shows each day at the Willard Smith Planetarium at Pacific Science Center. Find the schedule on our calendar page.

Star parties

There are four free public star parties on tap for the weekend. The Covington Community Park Star Party is scheduled for 7 p.m. Friday, February 3 at the park. This popular event presents a good opportunity for stargazing south of the city. It’s sponsored by Covington Parks and Recreation and supported by the Seattle, Boeing Employees’, and Tacoma astronomical societies. The Seattle Astronomical Society plans its monthly free public star parties for 6 p.m. Saturday, February 4 at two locations: Green Lake in Seattle and Paramount Park in Shoreline. These events are cancelled in the event of rain or cloudy skies. The Tacoma Astronomical Society holds its public nights whether it’s clear or not. One is coming up at 7:30 p.m. Saturday, February 4 at the Fort Steilacoom campus of Pierce College. The indoor presentation will be about 110 Celestial Objects. The telescopes will come out if weather permits.

Futures file

You can scout out future astronomy events on our calendar. We’ve recently added listings for:

Up in the sky

The Moon will join Venus and Mars in a pretty little grouping Wednesday, February 1. 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.

FacebookTwitterGoogle+EvernoteShare