Astronomer Discovers the Fourth Closest Star System to Us -- And It's Cool!

Just last year, I posted the news that astronomer Kevin Luhman of Penn State had discovered the third closest star system to our own.  It consisted of a pair of failed stars -- stars containing too little material to shine consistently with visible light and thus commonly called brown dwarfs.

Now Luhman has done it again.  He recently announced the discovery of the fourth closest system -- this one consisting of the coldest brown dwarf ever found.  Known only by a long catalog number giving its cosmic "latitude and longitude" (WISE J085510.83-071442.5), the wanna-be star is 7.2 light years away.  That's right in our neighborhood as far as astronomical objects are concerned.

Our best estimate of its mass is that it weighs only as much as 3 to 10 Jupiters.  So, really, it could be more of a free-floating planet rather than a brown dwarf.  But since brown dwarfs are more common (planets are found more frequently around stars than by themselves), the discoverer is betting it's just a very cold and poorly endowed brown dwarf.

The image accompanying this note is just an artist's conception of what such a cold, failed star might look like.  After observing it with a variety of space-based telescopes (such as WISE and Spitzer, which are sensitive to infra-red or heat rays and not light), Luhman and his colleagues estimate that the outer temperature of this strange neighbor is as cold as the Earth's North Pole.  (Estimates vary from -54 to 9 degrees Fahrenheit, or -48 to 13 Centigrade.)   So its outer layers are like those of the giant planets far from our Sun, and nothing like a real star.  Stars have temperatures thousands of degrees hot.

What is remarkable to me is that, after 400 years of using telescopes, and more than 50 years of instruments in space, we are still discovering our closest neighbors!  It's not our fault, of course -- this neighbor was very shy, not shining with the kind of rich light power that our closest neighbor, the triple star system Alpha Centauri, gives off.  And in space, as on Earth, it's often the show-offs that get the attention.

A Beautiful Pinwheel of a Galaxy

A Beautiful Pinwheel of a Galaxy

Taking a break from all the heavy-duty science news for a minute, I want to share a beautiful recent image with you from the Hubble Space Telescope.  What you see on our photo is a large part of a spiral shaped galaxy (or island) of stars, known by its catalog number M83. It is about 15 million light years away in the  constellation of Hydra, the water snake.  

M83 contains billions upon billions of stars and quite a bit of gas and dust -- the cosmic raw material from which new stars, new planets, and perhaps even new Facebook fans can form.

This remarkably detailed image emphasizes the pinkish-red regions that are glowing clusters (or groups) of young stars, seen on the edges of the galaxy's spiral arms.  Actually, the young (adolescent) stars in these clusters glow so hot, they give off not just the light our eyes can see, but also energetic ultraviolet light.  The left-over gas that still surrounds these new star groups (in a way, the womb that gave birth to them) then is set to glow.   The excited gas -- mostly the cheapest, simplest element in the universe, hydrogen -- glows with a characteristic pinkish red.

Just look at all the pinkish glow!  That is to say, see all the new stars that we can see having been born recently -- at least recently on the cosmic time scale, or somewhere between 1 to 10 million years ago.  Like most of our cities in the spring and summer, there is still lots of construction going on in such galaxies.  

First "Earth Cousin" Planet Found

Astronomers working with the Kepler telescope, led by Elisa Quintara of the SETI Institute, have announced the discovery of the first planet orbiting another star that meets the two characteristics we have been particularly waiting for.  The planet is Earth-sized AND it orbits its star in the zone where water is likely to be liquid (called the “habitable zone.”)

The planet and star have no name, but only a catalog number – Kepler 186.  Located in the constellation of Virgo, about 500 light years away, the star is “red dwarf” – smaller and cooler than the Sun.   So a planet has to be closer to it to have the right temperature for liquid water.  But every star has its own habitable zone and Kepler 186 is no exception.

We have actually found five planets around Kepler 186 so far, but the other four planets are very close to the star and much too hot for life as we know it.  Called Kepler 186f, the newly found planet takes about 130 days to go around its star, and its distance is in the zone where water could be liquid (if the planet has a significant atmosphere.)

Astronomers actually know of some 1,800 planets around other stars so far, orbiting at a wide range of distances and showing a wide range of sizes.  In the past, we have found a number of planets that were the same size as Earth but all of these were too hot – orbiting too close to their stars.  We have also found a number of planets that were in the habitable zone of their stars, but these were bigger than Earth.  Most likely they were so big they would look more like Neptune or Jupiter, made mostly of gas and liquid (or at least having a huge shell of gas and liquid before you could touch solid ground.)

Kepler 186f (sorry planets don’t get names yet) is the first planet that is both the right size and the right distance from its star.  Today, at their national press conference, the scientists who discovered it made sure not to call it an “Earth twin,” however.  Instead, they used the term “Earth cousin” to describe their discovery.  That’s because Kepler 186 is a cool red star, about half the size and mass of the Sun.  So the light of this star will look different on the newly discovered planet – instead of the yellow sunlight we are used to, anyone standing on the surface of Kepler 186f would see reddish-orange sunlight.  The scientists speculated whether any plants on the new planet would receive enough energy to do photosynthesis, and their first conclusion was a tentative yes.

What’s especially important about this discovery is that roughly 80% of all the stars in our Galaxy are red dwarf stars.  If, as our observations are starting to show, MOST stars will have planets, then most planets are likely to orbit red dwarfs.  So places like Earth and our Sun may be the exception.  And Kepler 186f may be a mainstream kind of world in the vastness of the Milky Way.

On our diagram, above, you can see the orbit of the Kepler 186 system’s planets to the same scale as the inner planets in our own solar system.  The fuzzy green region in each case is the habitable zone of each star. You can see the Earth comfortably in the habitable zone of our Sun, and 186f in the habitable zone of 186.  The painting of 186f in this picture is just from the artist’s imagination.  We really have no idea what the planet looks like.

(By the way, for those of you who like to count, you may wonder why the fifth planet in the Kepler 186 system gets the letter f, when f is the sixth number of the alphabet.  That’s because in this pretty awkward naming system we are using, the star is called Kepler 186a, and the letters of the planets start with b.  I don’t endorse this system, folks, I just explain it.)

What Would the Lunar Eclipse Have Looked Like from the Moon?

We who live in North or South America (and had clear skies,) experienced a total eclipse of the Moon Tuesday morning, April 15.  But what would the eclipse have looked like to someone on the Moon?

First, since the Moon always keeps one side toward the Earth and one side away from the Earth, we have to pick a side. For this purpose, the interesting side of the Moon is the one that was facing the Earth and the Sun. It was sunny and bright on that side of the Moon before the eclipse began. Then, an observer on the Moon would have seen the Earth move in front of the Sun, and darkness descend. It would have gotten colder too without the warmth of the Sun.

Since the nearby Earth looks bigger from the Moon that the Sun does, the Earth more than covered the Sun. Still, the Earth's atmosphere bends some of the sunlight behind it toward the Moon. So someone on the Moon would have seen a faint ring of light around the dark Earth. (If you had a telescope on the Moon, you might also have seen the lights of big cities and large fires on the night side of our planet.)

How do we know that this "Moon perspective" about the eclipse is right? A Japanese spacecraft called Kaguya captured just this kind of image during a lunar eclipse in February 2009, as it was orbiting the Moon. In the picture above (courtesy of the Japanese Space Agency), you see several views of the Earth from the Moon during the eclipse. The ring of light is not complete, because some part of Earth was below the Moon's horizon as seen by Kaguya. At the end of the eclipse, you can see the first light of the Sun coming out from behind the Earth, making a kind of diamond ring effect. How wonderful that our robot spacecraft can give us views in the solar system that earlier scientists could only imagine!

Apr. 14-15, 2014 Total Eclipse of the Moon Visible Throughout North America

I've put the information about this eclipse in question-and-answer format:

1. What Is Happening?

               Late on Monday evening and early Tuesday morning, Apr. 14-15, a total eclipse of the Moon will be visible from throughout the U.S.  In a lunar eclipse, the full Moon and the Sun are exactly opposite each other in our skies, and the Earth gets between them. This means that the Earth’s shadow falls on the Moon, darkening it.  (See the diagram above.) This will be a nicely democratic event; the eclipsed Moon will be high in the sky and easily visible (provided it’s not cloudy.)

2. When Will the Eclipse Happen?

Event	Pacific	Mountain	Central	Eastern
Partial eclipse starts	10:58 pm	11:58 pm	12:58 am	1:58 am
Total eclipse starts	12:07 am	1:07 am	2:07 am	3:07 am
Total eclipse ends	1:25 am	2:25 am	3:25 am	4:25 am
Partial eclipse ends	2:33 am	3:33 am	4:33 am	5:33 am

As the shadow of the Earth slowly moves across the Moon, we first see only part of the Moon darkening (partial eclipse).  When the Earth’s shadow completely covers the Moon, we see a total eclipse, weather permitting.  

The best times to watch probably start a half hour before total eclipse starts, by which time a substantial part of the Moon is eclipsed.  The whole total phase lasts 78 minutes this time, and it looks pretty much the same the whole time, so only the most dedicate eclipse buffs will stay up for the whole thing.

3. What is Visible During a Lunar Eclipse

               As the shadow of the Earth covers the Moon, note that our natural satellite doesn’t become completely dark.  Light bent through the Earth’s atmosphere still reaches the shadowed Moon, and gives it a dull brown or reddish glow.  The exact color of the glow and its darkness depend on the “sooty-ness” of our atmosphere – how recently volcanoes have gone off and how much cloud cover, storm activity, and human pollution there is around the globe.

               Also, as the Moon becomes dark, other things in the night sky become easier to see.  As you look toward the southwest, you can see Mars to the right of the Moon, the bright star Spica just below and near it, and Saturn off to the left. Here is a nice diagram from Astronomy magazine (click to make it bigger). 

(Note that this is drawn for 3 am Central Time, which is 1 am Pacific Time.)

4. Is it Safe to Watch, and How do I Watch?

               Since the Moon is safe to look at and eclipses make the Moon darker, there’s no danger in watching the eclipse with your eyes or a telescope.  (The more dangerous eclipse is the solar one, where it is the Sun that gets covered.) Lunar eclipses don’t require you to have fancy equipment or to go to a dark location.  Bring binoculars, if you have them, to see the Moon larger, but just your eyes are fine.  Take someone along with whom you like to spend time in the dark!

5. What Can I Tell My Kids (or Kid Brother or Sister)?

               Suggest that they take a careful look at the shadow of the Earth as it moves across the bright face of the Moon.  What shape is it?  The round shape of the Earth's shadow suggested to the ancient Greeks, more than 2000 years ago, that the Earth’s shape must be round too.  Eclipse after eclipse, they saw that the Earth cast a round shadow, and deduced that we lived on a round planet (long before we had pictures from space.) 

Also, if kids have to miss this eclipse, you can console them by letting them know that there will be another total lunar eclipse on Oct. 8^th, 2014 (and two more in 2015.)