Monthly Archives: June 2008

astronomy news, astrophysics, galaxies, Milky Way Galaxy

Gaining Clarity on the Milky Way

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Learning More about the Home Galaxy

Wow. I miss ONE AAS meeting, and they lose two spiral arms from our galaxy! This is what I get for staying home and working on two big projects with massive deadlines. I did manage to log in and watch the press conferences from the comfort of my overstuffed office, so I caught the gist of what has turned out to be a very cool story.

First, some background. For years, astronomers thought our galaxy probably had four spiral arms. But, it’s hard to tell because we can’t exactly SEE all of our galaxy in visible wavelengths. This is due to all the dust in the galactic plane, and since WE’RE in the galactic plane, it’s like trying to see through a dense fog when it comes to looking in various directions. Isaac Asimov put it best when he wrote, “In a sense, we are on a low roof on the outskirts of the city on a foggy day.”

Well, as it turns out, telescopes with infrared capability can look through that fog and see farther and sharper than visible-light counterparts. So, it makes sense to use such facilities when you want to see what’s out there.

Groups of astronomers from JPL/CalTech and the University of Wisconsin used the infrared-enabled Spitzer Space Telescope to look at the galaxy. Their survey, called the Galactic Legacy Infrared Midplane Extraordinaire (GLIMPSE), spanned 130 degrees in longitude (65 degrees on either side of the center of the galaxy), and 2-4 degrees in latitude. Since Earth is located about halfway out along the plane of a flattened spiral, this survey actually encompasses a large fraction of the volume of the Milky Way. The infrared views (shown below) show where the stars are, as well as the dust clouds in the plane, allowing a more complete star census to be done.

[GLIMPSE]

Here’s one of two views of the Milky Way from GLIMPSE, emphasizing wavelengths (3.6 – 8 microns) in the familiar blue-green-red that our eyes see, with the shortest wavelengths displayed in blue and the longest in red. For more technical details, check out the GLIMPSE page at the University of Wisconsin’s team site. They also have downloadable poster-size files of this and another view of the same data.

Milky Way Spiral StructureNow, if you could turn that image so we could see it from the “top down” this “artist’s concept” might be what our Milky Way really looks like. The survey showed, for the first time, that arms we thought were there, really aren’t. The Milky Way’s elegant spiral structure is dominated by just two arms wrapping off the ends of a central bar of stars.

Spitzer’s imagery of the galaxy comprises 800,000 snapshots, and when you piece them all together, they make the clearest view of the Milky Way ever produced. The team has created a poster that they showed at AAS that is 180 feet (289 meters) long and 3.5 feet (2.1 meters) wide. The poster is going on tour soon, apparently showing up at Griffith Observatory (where they have a similar large-scale image of a small part of the Virgo Cluster called “The Big Picture” on display), and then on to various other cities. You, however, can explore it from the comfort and privacy of your home or office by going to http://mipsgal.ipac.caltech.edu/p_map.html where they have a GoogleMaps zoomable map. Check it out!

astronomy news, astronomy research, exoplanets, exploration

Earth As An Exoplanet

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How We Might Look to the Neighbors*

*If They Had a Good Set of Instruments and a Clear View

RGB comp of deconvoluted frames of Earth and Moon

Astronomers are enjoying an unprecedented time of planetary discovery. As of May, 2008, here have been 293 planets found around other stars. That number will change, and in fact, it already has, and it’s only the 2nd of June.

These planetary discoveries have the potential to teach us a lot about how and where planets are scattered around the galaxy, and perhaps other galaxies as well. But, here’s what’s also cool–at least one mission out there, the former Deep Impact Mission to a comet–is now spending its time looking for other planets. And, once in a while it turns its eye back to Earth to look at our home planet as if it were an exoplanet. It’s not the first time a spacecraft has looked at Earth, but it is the first time one has done it with an array of instruments tuned to study the light from our planet (and others) in high detail.

The image here was taken by the spacecraft on May 29, 2008, and shows the Moon in its orbit around Earth. It shows our planet from the spacecraft-eye view; if a nearby civilization had a similar spacecraft and looked at us with it, they’d likely see a bright spot (if they could manage to separate us out from the glare of the Sun).  If they had a REALLY good instrument, they’d probably notice that our brightness would dim occasionally and periodically, almost like something is passing in front of us.

The idea behind looking at our home world as if it was an alien planet is so that we can use what we find to compare it to other planets we might find. If we can understand how we look to the neighbors (i.e. our color, atmospheric properties, distribution of continents and oceans) then it will help us recognize similar properties when we see them on other planets.

At the summer meeting of the American Astronomical Society, being held this week in Saint Louis, astronomers working on the EPOXI mission (using the Deep Impact craft) talked about their work. They said that later this summer they’ll release a time-lapse movie of the Moon transiting Earth. As it passes between Earth and the point of view of the spacecraft, it will cover up places like the deserts of North African, which reflect a lot of light.

To a distant observer, this kind of transit would show up as a dimming of the planet (which would actually appear pretty bright since its surface areas and clouds reflect light). This well-known transit effect is also how astronomers can “see” or actually infer the existence of larger planets around stars. The light blockage is what what helps them detect the existence of a planet. So, the story of planetary discovery keeps on ticking, like that well-known battery-operated bunny rabbit. There are, in fact, more results from the meeting that I’ll write about in another post. But for now, enjoy the pretty sight of Earth from “alien eyes” and think about what it will be like when we find another Earth out there.