Wednesday, August 24, 2016

Planet Discovered Around the Nearest Star

Astronomers at the European Southern Observatory are announcing today that they have found an Earth-sized planet orbiting the nearest star to the Sun, Proxima Centauri.  The star is only 4.2 light years away (which is roughly 25 thousand billion miles – that’s close for astronomers!)

The newly found planet takes 11 days to orbit its reddish star (compare that to Mercury, the closest planet in OUR solar system, which takes 88 days to go around the Sun.)   You might think that a planet that takes only a week and a half to orbit its star must be outrageously hot, but the difference is that Proxima Centauri is a much fainter and cooler star than the Sun.  So the planet could be in the star's habitable zone (liquid water may possibly exist on its surface.)

We found this planet, as we have many others, not by getting a picture of it, but by measuring the pull of the planet on the star.  As the planet circles the star, from one side of it to the other, the planet’s gravity, small as it is, makes the star wiggle just a little bit.  And it’s this wiggling of the star that we can detect from Earth and use it to estimate the mass (gravity) of the planet.

This method can only tell us the minimum mass that the planet must have, and that turns out to be 1.3 times the mass of the Earth. (The wiggle, by the way, only changes the motion of the star by about 3 miles per hour, toward us and then away from us.  That’s a tiny change, but modern instruments are able to make out changes in speed that small.)

A planet with that low a mass is most likely a solid rocky planet, like ours.  Being so much in the gravity embrace of the star, the planet may have one side permanently pointed toward it, much like our Moon has one side permanently pointed toward the Earth as it goes around us. The Proxima Centauri planet would then also rotate in 11 days, making its day and its year the same length!   That’s weird to think about.

The fastest planetary probe we have built so far would take something like 80,000 years to get to Proxima Centauri.   It’s hard to get graduate students to volunteer for that kind of trip!  But, as you may have heard, Yuri Milner, the Russian-American billionaire physicst, has, earlier this year, pledged a hundred million dollars for a research effort to develop a mini-probe, smaller than the smallest cell phone, yet with working instruments, that could ride powerful laser beams and get to the nearest star system in only 20 to 25 years.

Clearly, Project Breakthrough Starshot, as it’s called, will now focus on Proxima Centauri, the nearest of the three stars in the closest star system.  Bets have been on one of the other two stars (called Alpha Centauri, after the brightest in the pair) to have planets, but the first discovery belongs to Proxima.  What an exciting time to be alive.

Above is an artist's conception of what Proxima would look like from the planet's vantage point, and below is a diagram with key characteristics of the Proxima system compared to our own.

Saturday, August 20, 2016

Happy One Year Pre-Anniversary of the All-American Eclipse of the Sun

August 21 is exactly one year before the 2017 eclipse of the Sun which will sweep across one country and one country only -- the US. On a Monday morning (Aug. 21, 2017) this "All-American" eclipse (as it's being called) will begin on a beach in Oregon and cross the country diagonally to end in the afternoon on a beach in South Carolina.  See the map below.
The eclipse will be total (moon covering the Sun completely) only in a path about 60 miles wide and we expect huge crowds and traffic jams in that zone. The rest of North America (500 million people) will see a partial eclipse, with a big bite taken out of the Sun. Special eclipse glasses or ways of projecting an image of the Sun will be needed to see the partial eclipse safely.
The full story,in everyday language, with a map and times for major cities, and safe viewing guidance, can be found in a free 8-page excerpt from a book, called Solar Science, that Dennis Schatz and I wrote for teachers. It is at:
There is a national committee that I serve on trying to arrange a good experience with the eclipse for as many people as possible. Wish us luck! Dennis and i are also working with science teachers, libraries, and science and nature museums to become centers of eclipse information for their communities.
I'll say more about preparations for the eclipse on this page as the year goes on. But for now, you may want to note the date and if you have friends or relatives in the total eclipse zone, be extra nice to them starting now.
And thanks to Prof. Tyler Nordgren of the University of the Redlands for permission to use his cool poster.
Map of the 2017 Total Eclipse Path
For those of you who are teachers, or who know a teacher, we will be doing a webinar on how to prepare yourself and your students for the eclipse.  For more see:

Friday, August 12, 2016

A Sparkling Cluster of Stars from the Hubble

Here is a beautiful new image from the Hubble Space Telescope, showing a young cluster of stars called Trumpler 14.
Located about 8,000 light years away in the constellation of Carina, this grouping of hot bright stars formed only recently from a great cloud of cosmic raw material, called the Carina Nebula. It is one of the great ideas that we now know about how stars live that the more massive a star, the brighter it shines, and the shorter its life-span will be before it "burns out." Superstars die first, is the general rule.

Because Trumpler 14 formed only about 500,000 years ago (which is a very short time on the cosmic scale), this group still includes a lot of bright superstars, which dominate our image.
Robert Trumpler (1886-1956) was a Berkeley astronomer, who compiled a very useful list of star clusters (places where dozens to thousands of stars are born together.) An annual award at the Astronomical Society of the Pacific, honoring the best PhD thesis in astronomy in North America, is named in his honor.
In our picture, you can see a jewel-like display of bright stars in front of the glowing gas and dust of the nebula. The stars in this cluster are one ten thousandth the age of our Sun. Mere babies, really!

Click on the photo to enlarge it and see it even better.  

Saturday, August 6, 2016

Perseid Meteor Shower May Show an Outburst

This Thursday and Friday, there will be one of the best annual meteor showers you and your family can watch -– the Perseids.    And some experts are even predicting that there might be a meteor “outburst” this year –- where the number of shooting stars increases beyond the usual rates.

This is a complicated year for watching the Perseid meteor shower, because the evening sky has a roughly half-lit-up moon in it, making it more difficult to catch the faint “shooting stars.”  So if you can wait until the Moon sets (between midnight and 1 am), you should have better viewing in the pre-dawn darkness.   (That’s great advice for people on camping trip and insomniacs, but probably not useful for those who have to get up for work.)

The best night is the evening of Thursday, Aug. 11 and morning of Friday, Aug. 12th, although there could be significantly more meteors in the sky on the night before and the night after too.  Meteors or “shooting stars” (which have nothing to do with stars) are pieces of cosmic dust and dirt hitting the Earth’s atmosphere at high speed and making a flash of light.  These flashes could happen anywhere in the sky, so it’s best to view the shower from a wide-open place.  See the list at the end for viewing suggestions.

The Perseid meteors are cosmic “garbage” left over from a regularly returning comet, called Swift-Tuttle (after the two astronomers who first discovered it).  The comet itself returns to the inner solar system every 130 years or so; it was last here in 1992.  During each pass, it leaves dirt and dust behind and it is this series of long dirt and dust streams that we encounter every August.  Some scientists who study comets and meteors are predicting that we might briefly encounter an especially crowded part of the debris stream this time.

Each flash you see is a bit of material from the comet hitting the Earth’s atmosphere and getting heated up (and heating up the air around it) as it speeds through our thick atmosphere.  Both the super-heated dust and dirt and the heated air contribute to the visible light we observe.  Since comets are left-overs from the early days of our solar system, you can tell yourself (or your kids) that each flash of light is the “last gasp” of a bit of cosmic material that formed some 5 billion years ago.


1. Get away from city lights and find a location that’s relatively dark
2. If it’s significantly foggy or cloudy, you’re out of luck
3. Your location should allow you to see as much of the dome of the sky as possible
4. Allow time for your eyes to get adapted to the dark (at least 10 -15 minutes)
5. Don’t use a telescope or binoculars – they restrict your view (so you don’t have to be part of the 1% with fancy equipment to see the shower; this is a show for the 99%!)
6. Dress warm – it can get cooler at night even in August (and don’t forget the insect repellent while you are outside)
7. Be patient (it’s not fireworks): keep looking up & around & you’ll see flashes of light
8. Take someone with you with whom you like to spend time in the dark!