Saturday, December 30, 2017

New Year's Day Will Have a Supermoon

By a cosmic coincidence, the first day of 2018 will have a nice full Moon in the evening. And the full Moon occurs just when the Moon is closest to the Earth in its monthly orbit, so it will look a little bigger to us in the sky.
Since 2011, the media have followed a suggestion by an astrologer (!) and started calling these slightly closer full Moons "Supermoons" -- a name more likely to make people notice. We astronomers tried to fight the term, but we're mostly giving up.

On January 1, the Moon will be closest (at perigee) at 2 pm, Pacific time: it will be 221,600 miles from us. (The average distance is about 239,000 miles.) The full Moon officially happens only 4 hours or so later, at around 6 pm Pacific time.
So when the full Moon rises, in the evening, as the Sun sets, it will looks somewhat bigger and brighter than usual. It's no big deal, except to reporters eager to fill news copy during the holidays when news is slow. Still, it's always nice to have an excuse to notice the full Moon and show it to kids in your family or neighborhood.
Remember, the Moon is the only world other than Earth on which humans (12 of them) have stood and explored. Even just with your naked eye (but better with a pair of binoculars), you can see some of the bigger round craters on the Moon, evidence of the ancient violence that was common in the early days of the solar system. More than four billion years ago, large chunks of rock and ice were still moving around the system, hitting the forming planets and moons.
January 2018 is a blue-moon month (meaning two full moons will happen in the same month) and the second full moon, on January 31, will be more impressive. It will include not only a Supermoon, but a total eclipse of the Moon!
That eclipse will be best on the West Coast, but it will happen early in the morning. So you'll have to get up at 5:30 or 6 am on a Wednesday morning to see the full Moon fully eclipsed. I will have a much more detailed preview of the eclipse in this column when it's a closer in time.
Our photo, by astro-photographer Rick Baldridge, shows a full Moon seen above the historic Lick Observatory near San Jose.  Click on it to see it bigger.
On a personal note, I have just launched my own astronomy website at and invite you to check it out. It's still a work in progress.

Tuesday, November 28, 2017

First Visitor from the Realm of the Stars Ever Found Is Oddly Shaped

Astronomers around the world have been observing a small but fast object that gives every indication of coming from some other star system. It's the first such "interstellar" visitor we have ever observed. And it's characteristics are quite unexpected.
Most astronomers expected the first such deep-space visitor to be a comet -- a chunk of icy material (which our solar system has in great abundance outside the orbits of the main planets.) But all the characteristics of this visitor argue against that idea. It didn't evaporate and develop a "tail" as it came closer to the Sun than Mercury. Any comet would have done that.
And it seems to spin in less than 8 hours. Something made of snowballs or ice might fall apart from such a fast spin. So it appears that our visitor is made of rock -- more like an asteroid and not like a comet. And its color is dark and reddish, like some asteroids we have seen from our own system.
Furthermore, its shape -- which we can estimate from the way the sunlight reflected from it changes -- is also odd. It appears to be much longer than it is wide. Our best estimate is a cigar shape (see the attached painting from the European Southern Observatory), perhaps half a mile long and only 80 yards in diameter. But it could also be a flat cylinder -- which reminds some people of the shape of the main body of the Starship Enterprise.
(Just to be sure, astronomers at the SETI Institute used their antenna array in Northern California to check if the visitor was sending any radio messages. Nothing was found.)
First discovered by a team led by Karen Meech of the University of Hawaii using a Hawaiian telescope, the visitor has been given a Hawaiian name: Oumuamua, which means "scout or messenger, arriving first" -- not a bad fit. Its scientific designation is 1I2017U1. The 1I stands for first interstellar object ever discovered!
When we found it on Oct. 19th, it was coming in fast from the direction of the constellation of Lyra. It's now going out at a speed of 86,000 mph relative to the Sun. It already crossed the orbit of Mars and will reach the distance of Jupiter in May 2018. Having been whipped around by the Sun's gravity, it will go out in a new and random direction, back toward the realm of the stars.
We expect that such visitors should be passing through all the time, but we haven't discovered them until now. With new surveys of small, dim objects in the sky soon getting under way, we expect to find a lot more small pieces from our own neighborhood -- and beyond. Stay tuned.

Monday, November 6, 2017

A Beautiful Star Cluster for Dark Times

As many readers switch from Daylight Savings Time to find darker evenings awaiting them, here is a beautiful new image from the Hubble Space Telescope. We see a "globular cluster" with the catalog name M5 -- an ancient collection of stars, with about 100,000 of them visible on this remarkable photo.
The image combines views taken with visible light and infra-red cameras, and highlights some of the younger bluer stars sprinkled among the older yellower stars that make up the majority of the cluster. This grouping is about 25,000 light years away and was born 12-13 billion years ago.
It was about 100 years ago that Harlow Shapley, one of the greatest astronomers of the 20th century, used such bright globular clusters to map the extent and shape of our Milky Way Galaxy and to demonstrate conclusively that the Sun and the Earth were not in its center.
Such a beautiful picture can help remind us that there is a larger perspective out there, and help us put aside thoughts of the crazy things we seem to be doing to each other and to our fragile planet on almost a daily basis. Click on the pictures to see them bigger.  The diagram below shows how the globular clusters, distributed above and below the plane of our Galaxy, help outline its shape and extent.

Sunday, October 15, 2017

A Ring Around the Dwarf Planet Haumea

European astronomers have announced the first discovery of a ring around a dwarf planet. Dwarf planets are similar to Pluto, in that they are small and hang out in a zone with others of their kind. This one, Haumea, is beyond Neptune, taking 284 Earth years to go around the Sun.
The ring is very faint, but astronomers at the Institute of Astrophysics of Andalusia were able to find it when they saw Haumea cross in front of a star. The star’s light went out not only when Haumea crossed in front of it, but briefly before and after, indicating a ring was present.
All four of the giant planets in our solar system have rings, but this is the first found around a smaller planet. Its cousin Pluto definitely doesn’t have one, because we looked when the New Horizons probe went by it.
Haumea is named after the Hawaiian goddess of childbirth and has another oddity. It spins so rapidly – taking less than 4 hours for one spin -- that it doesn’t look exactly round, but more oval shaped. It’s the least round of any world we know bigger than about 60 miles across. It has two known moons, and now a ring too. The zone past Neptune, called the Kuiper Belt, is just getting more and more interesting.
(Our illustration is NOT a photo, just an artist's impression, based on what we have observed so far.)

Wednesday, September 13, 2017

Cassini Space Probe To Fall Into Saturn Friday Morning

Friday morning, around 5 am Pacific time, NASA will send the Cassini space probe falling into the planet Saturn -- until it is crushed by the pressure in the ringed planet's atmosphere. NASA is commanding Cassini to "commit suicide" before its propellant runs out and it can't be steered any more. Since Saturn has two moons which might harbor some sort of primitive life, we wanted to make sure we did not contaminate those worlds.

The planet Saturn is made mostly of gas and liquid (and its make-up is dominated by the two lightest elements in the universe, hydrogen and helium.) So you can't land ON Saturn, you can only fall INTO Saturn (like a giant ocean world.)
Cassini has been orbiting Saturn for 13 years, sending back amazing pictures and information on the planet, its complicated rings, and its 62 moons. It's made a slew of remarkable discoveries, including the presence of warm salt-water geysers on the relatively small moon called Enceladus, and lakes and rivers of liquid fuel oil on the giant moon Titan. It was launched 20 years ago (so it's had a long and fulfilling life for a spacecraft.)
Since April, it has been swooping in and out of the space between Saturn's cloudtops and its inner rings, an area we had never had the nerve to explore before. NASA estimates the spacecraft has traveled almost 5 billion miles in total and has sent back more than 450,000 picture (that's a Flickr file not even your most picture-taking relatives can compete with!)
In our image, you can see Saturn and its complex ring system, with a painting of the spacecraft above the planet's north pole, ready to make a dive.
Some of my favorite pictures in the introductory astronomy textbook I am the lead author on come from Cassini (which was the most complicated planetary explorer ever built.) On Friday morning, let's give it a thought as we wake up -- we'll miss you, Cassini!
You can see live coverage of the last days of the mission on NASA TV at:
You can access the image galleries and latest videos from the mission from this page (designed for the media, but which anyone can use):
By the way, you can access my free textbook at : 

Monday, September 4, 2017

Double Eclipse of the Sun; Eclipse Statistics

My favorite picture so far of the recent eclipse of the Sun is the one you see with this post. Photographer Simon Tang (who gave me permission to reproduce it here) took a sequence of photos from Huron, California, recording the International Space Station crossing the face of the Sun just as the Moon was eclipsing it.
Each of the images of the Space Station is less than 1/1000th of a second long, since the Station moved across the Sun in less than a second. The image is taken in H-alpha, a specific color of light emitted by hot hydrogen atoms in the Sun's lower atmosphere. You can see the Station close up in our second image.

NASA reports impressive statistics for the Aug. 21 eclipse: 90 million page views on NASA's two websites, 40 million views of the live broadcast, 3.6 billion users on social media, and the most popular Instagram image ever -- all of a celestial event with no politics, no national or religious affiliation. It was just nature, doing its thing, predictably, reliably, spectacularly.
In our own project, 2.1 million eclipse glasses were distributed to 7,100 libraries -- all to be given away free to the public. I was one of the astronomers leading the effort, and want to thank the Moore Foundation, Google, and NASA, for supporting the program to allow public libraries to help their patrons observe the eclipse safely. If only we could come together this well about other things!

Click on the images to see them bigger.

Wednesday, August 23, 2017

A Short Eclipse Mega-movie Already Available

A first 2.5-minute version of the Google Eclipse Megamovie is now out and can be viewed at:
This is actually version 2, which shows a map at the bottom right indicating where along the path of the total eclipse in the U.S. each image comes from. The team soon expects to have a much longer version with many more pictures taken during the 1 hour 37 minutes that the eclipse was over the continental U.S. stitched together.
So far over 6,000 images from the serious photographer volunteers, over 11,000 images via the online image upload from the public, and over 45,000 images via the App the team developed have been received, according to a message I got minutes ago from project leader Laura Peticolas of the University of California, Berkeley's Space Sciences Lab. What a nice example of citizen science!
I hope you all had good eclipse viewing Monday. I was in central Oregon with family and friends, and got a spectacular view of the total eclipse, with beautiful red prominences (great fountains of hot material being driven outwards from the surface of the Sun) visible through binoculars. The attached image above, from one member of our group, Dr. Cary Sneider, gives you a little taste of what we saw.
The other attached image, below, by Anna Rich, shows a car on the highway, on its way home from Oregon, expressing a sentiment many felt.
For anyone who missed the lead-up to the eclipse, a fun way to get caught up might be my conversation with veteran newscaster Gil Gross, at:
This eclipse special might be the first of a series of podcasts we will do on astronomical news and ideas, starting later in the fall. Stay tuned for more on what the producer's are calling "Fraknoi's Universe."

Sunday, August 6, 2017

Eclipse of the Sun Coming in 2 Weeks! And Another in 7 Years!

The path from top left to bottom right is the Aug. 21, 2017 eclipse
The path from bottom left to top right is the Apr. 8, 2014 eclipse

In just two weeks, on August 21, all of North America will experience an eclipse of the Sun. The eclipse will be total on a narrow path going across the U.S. from Oregon to South Carolina. The rest of the continents will see a partial eclipse, with a big bite taken out of the Sun by the disk of the Moon.
If you don't get to see this one, there will be another U.S. total eclipse in only seven years (on April 8, 2024.) If you missed out getting a hotel room or a campground in the zone of totality for August's eclipse, you have no excuse now for 2024! (See the attached map; click on it to see it bigger.)
I've had the opportunity to do quite a bit of media outreach for the eclipse; you can:
1. hear me as part of the eclipse special on the "Big Picture Science" radio show:…/eclipsing-all-other-shows
2. see me speaking on the eclipse at the SkeptiCAL convention sponsored by the Bay Area Skeptics:
3. read my comments as part of legendary science journalist David Perlman's last science article (David, who covered science news at the San Francisco Chronicle, is retiring at the age of 99! May we all have a career as long and respected as his.):…/Total-solar-eclipse-to-create-…
This week many media and people are waking up to the coming of the eclipse at last. Our free 8-page booklet all about it and how to view it safely can be downloaded from the page: Do read through it to get hints about how best to see and explain this rare sky phenomenon.
A free app, called TOTALITY, can be downloaded from both the Apple and Android app stores, and it will tell you exactly when and how the eclipse will be visible in your location.
If you haven't yet gotten safe eclipse-viewing glasses, your first stop should be your local public library. (Thanks to the Moore Foundation and Google, our project to distribute 2.1 million eclipse glasses has gotten glasses to almost 7,000 public libraries nationwide.)
If your library doesn't have any, here is a page to tell you all the reliable sources of eclipse glasses that are certified to meet the standards for protecting your eyes set by eye-doctors:
And for kids, please forgive me if I mention our children's book, "When the Sun Goes Dark," now in its fourth printing. Copies have temporarily run out in some places, but the publisher has it at:
Here is wishing you clear skies for August 21.

Eclipse stamp issued by the US Postal Service
changes the picture you see when you touch it

Tuesday, July 11, 2017

New Hubble Image of Jupiter's Red Spot

Astronomers are eagerly awaiting new information about the Great Red Spot, the largest and most colorful storm in the atmosphere of the giant planet Jupiter. The Juno spacecraft just flew as close as 5600 miles over the Red Spot, and the information is coming slowly back to Earth. This giant storm is currently about 10,000 miles wide -- larger than the entire planet Earth -- although it is smaller than when the Voyager spacecraft flew by in the 1970's. Why it has been shrinking and why it's color is so vivid are mysteries planetary scientists are trying to solve. 
In the meantime please enjoy the attached Hubble Space Telescope image of Jupiter, taken on April 3, when the Earth was closest to Jupiter in its yearly orbit. The Red Spot is vividly clear on this wonderfully detailed image, taken from just a few hundred miles above our planet's surface.  (Click on the image to see it bigger.)

Wednesday, June 21, 2017

Eclipse Talk on YouTube and New Kind of Eclipse Stamp

We are exactly two months away from the eclipse of the Sun that is coming to North America on August 21, 2017. I gave an illustrated, non-technical talk on the eclipse in the Silicon Valley Astronomy Lecture series, and it is now available on YouTube at: The talk has lots of information and visuals on where and how the eclipse will be visible, how to watch it safely, and how the U.S. is preparing for the huge crowds that are expected in the narrow zone where the eclipse will be total.
   Yesterday, the U.S. Postal Service issued its first ever "thermochromic" stamp in honor of the eclipse. That means when you touch the picture, it changes. Clearly this is a stamp every science will want to have. You can get them at your post office or by mail through:
   If you have not planned for the eclipse yet, now is the time to start thinking about where you will be on Monday, Aug. 21 and how you and your family or colleagues will observe the eclipse. In the video, I explain what is happening and give suggestions for safe viewing techniques. (Remember, any time any part of the Sun is showing, it's not safe to look at with just your eyes or sunglasses.)
   Thanks to grants from the Moore Foundation and Google, three astronomy colleagues and I were able to distribute 2 million safe eclipse-viewing glasses to public libraries nationwide. Check with your library to see if they are participating. The free booklet for libraries can be downloaded by anyone at: 

Sunday, May 28, 2017

New Views of the Planet Jupiter

The first results are in from the Juno mission exploring the giant planet Jupiter, and there are many surprises.
Look at the beautiful image here (click on it to see it bigger), showing the first detailed views of Jupiter's south pole region. The colors are a bit exaggerated, but the structures are real. You are seeing giant cyclones and anti-cyclones, as large as 600 miles across! That's extreme weather the 11 o'clock news team doesn't even dream about.

I'll remind you that Jupiter is not a solid planet -- most of it is made of gas and liquid. Yet there is enough material inside the giant planet to make 318 Earths. Scientists did not know whether at its very center it might have a small solid core or not. Heat from within rises and various molecules move up and down, producing complex bands, zones, and storms in the upper atmosphere.
Additional Juno discoveries include that Jupiter has a bigger core than expected, but that it has a fuzzy-looking structure, as if it were not sharply defined. The giant magnet inside Jupiter that surrounds it with the most powerful magnetic zone of any planet was also found to be stronger than anticipated.
Furthermore, the northern and southern lights on Jupiter are excited not only by charged particles captured from space (as we have on Earth) but also, unexpectedly, from charged particles coming from inside Jupiter.
As usual, when we get better instruments focused on a world or process in astronomy, we find that some of our old assumptions or ideas will need to be revised. That's what makes astronomy so much fun.

Below is an image showing 14 days of the Juno spacecraft approaching and then moving further away from Jupiter's cloudy atmosphere. (Click on it to make it bigger.)

Sunday, May 14, 2017

A Weird-looking Moon in a Gap in Saturn's Rings

Since 2004, the sophisticated Cassini spacecraft has been orbiting Saturn, sending back remarkable pictures of the planet, its rings, and its moons.   Now, with its fuel running out, the little spacecraft is being directed closer to Saturn’s rings, to get us even better views of this spectacular region (before Cassini does a Kamikaze dive into Saturn Sept. 15th.)

The image above is a fantastic close-up of one of the strangest moons we have ever seen.  The small moon Pan orbits inside the Encke Gap, an emptier region in Saturn’s bright A ring (Saturn’s different rings are given letter names.)  Pan looks like a “flying saucer” – with a set of high ridges around its equator.  It's about 22 miles across at its widest point.

Astronomers think that Pan formed inside Saturn’s ring and, as it grew, its gravity helped clear out the material in the gap which it now rules.  But there was enough material still in the flat ring neighborhood that it fell onto Pan’s equator and made the giant ridges that make Pan so distinctive.

Over the next few months, as scientist program Cassini to dive again and again into the space between Saturn’s and its rings, we will continue to get better images of “things in the rings” (sounds like Dr. Seuss) than we ever have before.  It’s a fitting finale for a spectacular space mission.

The image below shows you the neighborhood.  You can see Pan, its shadow, the Encke gap, and the A ring.  

Sunday, April 16, 2017

A Mini-Pluto at the Edge of Our Solar System

Astronomers have better measurements now of what is turning out to be a smaller version of Pluto located so far away that it may take 1,100 years to orbit the Sun. Nicknamed D.D. (or DeeDee) for Distant Dwarf, this remarkable small world appears to be about 400 miles in diameter -- only about 1/4 the size of Pluto, but possibly still big enough to be round like a planet.
D.D. was found in the fall of 2016 by a team of astronomers led by David Gerdes of the University of Michigan. As so often happens in astronomy, they were looking for something completely different, but found D.D. as part of their work. Now they have used an array of radio telescopes, called ALMA, to measure D.D.'s size and also to estimate its temperature. Ninety-two times as far from the Sun as the Earth is, D.D. is thought to be at minus 405 degrees Fahrenheit (minus 243 degrees Celsius; or only 30 degrees above nature's limit, absolute zero.)

D.D. is part of a whole zone of icy objects out beyond Neptune (astronomers call them Trans-Neptunian Objects or TNO's,) About 2,000 TNOs are now known, but most of them are too small and irregular (knotty potato-shaped) to be called dwarf planets. Pluto, the first TNO dwarf planet, was discovered in 1930, but in the last decade of the 20th century and the first decade of the 21st century, others were found, including Eris, Makemake, and Haumea. (If the names sound unusual, it's because we are trying now to name these outer worlds after mythological beings from many cultures, not just the ancient Greeks or Romans!)
We need more observations of D.D. before we are ready to call it a dwarf planet. If you thought that Pluto was being insulted when we called it a dwarf planet, perhaps it will help you to know that Pluto is the "first" of a whole new category of worlds. Five dwarf planets are now officially recognized by the International Astronomical Union, and at least six other worlds out beyond Neptune may eventually be included in the group. It may be years before we know if D.D. will join them.

But it's wonderful to see the Sun's family growing in this way, with our new instruments and surveys able to find worlds that literally are "far out!"

Sunday, March 26, 2017

Two Million Free Eclipse Glasses through Libraries (and a Free Booklet)

As you may know, there will be a rare eclipse of the Sun on August 21, 2017, and it will be visible throughout the United States. A spectacular TOTAL eclipse will be seen on a narrow path (about 70 miles wide) from Oregon to South Carolina. The rest of the U.S. and North America will see a PARTIAL eclipse, where only a part (but a substantial part) of the Sun is covered by the Moon. To look at the Sun when part of it is showing, special (but not expensive) glasses are required or you could damage the sensitive tissue in your eyes.
Millions of people will need glasses on August 21, and for the last year I have been grappling with the issue of how to get glasses to as many people as possible. Now, I am delighted to tell you that several astronomy colleagues and I have been able to get funding for glasses to be distributed through public libraries nationwide.
Thanks to the generosity of the Gordon and Betty Moore Foundation near San Francisco and Google, two million safe eclipse glasses will be made available through public libraries. Each library will get a supply of glasses to share free of charge and a booklet all about the eclipse and how to explain it to the public. The booklet, which I wrote with my colleague Dennis Schatz, is now ready and can be downloaded free at:
The first part of the booklet explains all about eclipses, the August eclipse and when and how it will be visible in different parts of the country, and how to observe it safely. It's written for beginners in science, so we hope everyone can benefit from it. The second part consists of information to help librarians plan public programs around the eclipse.
You could do your city or town a big favor by taking the booklet or just its web address in to your local library and encouraging them to participate in the eclipse and the glasses giveaway. Libraries can register for the program (through the STARNet Library Network at the Space Science Institute) at the website:
If, for some reason, your library can't participate in the program, there is information in the booklet on how to get eclipse glasses from the companies that manufacture the certified safe glasses that will protect you and your family's eyes. This spring is the time to make plans for where you will be and what you will do when the eclipse arrives on August 21.

Sunday, March 19, 2017

Bubbly Burp Tracks Giant Black Hole's Last Meal

Observations with a number of telescopes, including the Hubble, have now dated a kind of burp in the eating habits of the giant black hole at the center of our Milky Way Galaxy. It appears that about six million years ago, the central black hole "ate" a large cluster of stars and the neighborhood around it was energized by the process of the meal.

Black holes are regions where material (starting with dead stars) has collapsed so much, that nothing, not even light, can get out. The black hole at the center of our Milky Way now includes enough material to make more than 4 million stars like the Sun! It's what we call a "supermassive black hole" and lurks in the middle of our Galaxy like a giant speed trap for unwary stars or star groups that get too close.
As material is in the process of being "swallowed" by the black hole, it glows with desperate radiation, just before it falls in and disappears from view. A great bubble produced by the black hole as it ate its last serious meal has now been tracked by astronomers with much greater precision.
Just like the sound of the burp your uncle makes (after a heavy Thanksgiving meal) can travel through the dining room, so the bubble from this last meal can be seen traveling through the Galaxy like a giant expanding shell. The shell was probe by the Hubble as the light of distant objects raced through it and astronomers were able to measure the speed of the bubble's motion.
Six million or so years ago, it appears that a large clump of stars or gas (the raw materials of stars) was consumed by the black hole, making two "Fermi bubbles" in the Galaxy. Since then, the black hole has only been "snacking" -- tearing apart and eating an occasional star or random bit of gas. But no serious meal has made a big bubble from the mouth of the black hole since then.
Our diagram shows how in the six million years since that meal, the bubble has expanded at speeds of two million miles per hour and made a giant bubbles north and south of the black holes that extend for tens of thousands of light years. That kind of puts your uncle's last burp into perspective!

Wednesday, February 22, 2017

A Star With SEVEN Earth-like Planets

An international team of astronomers today announced that they have found a faint cool star that is surrounded by a system of seven planets, each of which resemble the Earth in size. Three of the planets orbits in what we call the "habitable zone" where water can be liquid and temperatures might be right for life.
The star, located about 40 light years away, is so faint and cool, it doesn't have a name like bright stars do. It's referred to by the name of the telescope that discovered it and given a number (TRAPPIST 1). Each of the planets is then given a letter from b to h. (See the diagram above.)
Note that the planets are all very close to their dim star, taking from 1.5 days to about 20 days to orbit it. (By comparison, the closest planet to the Sun, Mercury, takes 88 days to orbit.) Planets e, f, and g are the ones where the combination of a cool little star and close-by planet work out to make the temperatures potentially reasonable for life. This star enters the record books as the one with the largest number of Earth-like planets, and the largest number of candidate planets in the habitable zone.
Astronomers caution that the kind of star these planets live around (called an "ultra-cool red dwarf") tends to have a lot of "activity" on its surface when they are young. Great flares of energy and particles are given off in this kind of activity, which might flood the nearby planets with high-energy radiation. That might not be so healthy for the formation of life there until the star settles down to a more stable adult existence.
On the other hand, such low-mass stars (this one contains only 8% of the "stuff" our Sun has) tend to live much much longer than a star like the Sun, so there may eventually be a much longer opportunity for the planets to evolve their surfaces and atmospheres and give birth to life.
Another complication for planets so very close to their star is that their motion probably resembles that of our Moon in a crucial way. The Moon (and these planets) take the same time to orbit as to spin, which means they keep the same face toward the object they go around. So one side of each planet always faces their star and the other side is always in darkness. There is no day and night cycle on these worlds -- you either live on the star-facing side and have perpetual day or you live on the other side and have perpetual night. Only a significant atmosphere might make such a world more bearable and astronomers are using a variety of telescopes to probe whether these planets are surrounded by an air layer and how much and what kind of air they have.
Just to put the discovery in context, astronomers now know over 3,000 planets orbiting other stars, ranging from balls of gas and liquid much bigger than Jupiter, down to rocky balls smaller than Venus. Experts now estimate that perhaps half of the stars in our Milky Way Galaxy may possess planets, and many stars will have more than one planet, just like TRAPPIST 1 and the Sun do. The universe seems rich with planets of all kinds, making it more likely than ever that we are not the only form of semi-intelligent life in the cosmos.

Below is a little poster NASA created to show how the other planets in this system would look from the surface of one of them.

Sunday, February 12, 2017

Why Should I Believe a Word of This?

        In June of 2016, the students at my college asked me to be the Commencement Speaker. I was honored and touched, and talked about skeptical thinking and living a fact-based life. The newsletter "Skeptical Briefs" has just published a one-page version of my talk and I've put it up on the web, in case anyone might like to read it: 

Wednesday, January 18, 2017

A New Photo of the Death-Star Moon

Just in time to anticipate the success of the Star Wars film "Rogue One", NASA released a new photo of Mimas, the moon of Saturn's that resembles the "Death Star."
Mimas, an icy world about 250 miles in diameter, has a giant crater on it which is 86 miles across. That's a single impact feature that is one third the diameter of the world that it’s on!!  Astronomers speculate that if the chunk that hit Mimas, exploded, and dug out that crater had been a little bit bigger it might well have shattered that moon.  Then Saturn might have had another ring system around it.
The crater has been named “Herschel” after the astronomer (and musician) who discovered Mimas.  In its center is a mountain that towers almost as high as Mount Everest on Earth.  It’s that central peak that helps our mind’s eye see Mimas’ resemblance to the evil superweapon in the Star Wars series.
The photo was taken in October by the Cassini mission, which has been exploring Saturn, its rings, and its moons since July 2004.  Its spectacular images find their way into every course I teach and every tourist tour of the solar system I guide in my public lectures.

Sunday, January 8, 2017

A Photo of the Earth and Moon from Mars!

   NASA has just released a remarkable image of the Earth and the Moon as seen from a spacecraft orbiting Mars. Our planet and Mars were 127 million miles apart when the photo was taken.
   The Mars Reconnaissance Orbiter (MRO) has been orbiting Mars since 2006, collecting very detailed close-up images and data about the surface of the red planet. In this case it was used to capture a photo of Earth and Moon with both bodies in the same frame. The image was taken at a time when the Moon was behind Earth as seen from Mars, so it shows the Earth-facing side of our natural satellite.
   Even at Mars' distance, the image of the Earth reveals continents. Australia is the reddish-brown feature in the center. Seeing ourselves as a tiny disk of light in the blackness of space can help remind us that we share a fragile and beautiful planet in our journey through space.