THE SOUTHWORTH PLANETARIUM
207-780-4249      www.usm.maine.edu/planet
70 Falmouth Street     Portland, Maine 04103
43.6667° N                   70.2667° W
Founded January 1970
Julian date:  2457647.16

            "Much more to know than could ever be known."

THE DAILY ASTRONOMER

Thursday, September 15, 2016

Gaia's First Billion Stars

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"WATER ON ASTEROID 24 THEMIS"
Thursday, September 15, 2016

7:00 p.m. at the Southworth Planetarium

The 2016-17 Southworth Science Lecture Series

begins tonight with Dr. Julie Ziffer's presentation about

the discovery of water ice on the asteroid 24 Themis.

Dr Ziffer was part of the research team that made this discovery.

She'll discuss this research tonight.

Doors open at 6:30 p.m.

Admission by donation.

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"Exciting" doesn't begin to describe it.    "Fantastical,' is, perhaps, a bit more apt.     The European Space Agency's Gaia satellite has just released its first catalog, one containing more than one billion stars within our own galaxy.        Compiling this catalog is but the first step in the ESA's  ultimate goal to develop the most comprehensive galaxy map ever constructed.    

This collection was gathered over more than a year, from July 2014 -just after its deployment- to September 2015.      Not only does this catalog contain the positions of approximately 1.142 billion stars, it also has precisely determined the distances and motions of more than two million stars.    These motion and position determinations will enable the ESA to model the dynamics of our galaxy , so as to better understand the spiral arm motions and formations.    

​Gaia's first sky map.  The first catalog the Gaia satellite has produced.  Showing more than one billion stars, this compilation is a forerunner to much more extensive catalogs of the Milky Way Galaxy.  Image. ESA

Gaia has also conducted a more thorough study of open or galactic star clusters.   Whereas the Hipparcos catalog measured the positions and distances of  80 clusters out to a distance of 1,600 light years, Gaia's reach has extended out to 400 clusters over a distance of 4,800 light years. Analysis of more than a dozen star clusters has revealed that the clusters' outermost stars are farther from their centers than originally thought.   Astronomers know that the stars within an open cluster will eventually escape the cluster and join the galactic star streams.   Our own Sun was born into and eventually moved away from a cluster billions of years ago.

Through its five year mission, the Gaia satellite will capture images of even more distant stars and star clusters.    It will also provide astronomers with data on variable stars that will help them more accurately calculate stellar distances.    For instance, astronomers can use cepheid variable stars to measure distances to remote locations, such as the Large Magellanic Cloud, a satellite galaxy to the Milky Way.    Cepheid variables vary in luminosity, or absolute brightness.     This brightness relates directly to the star's variability period:   the longer the variability, the intrinsically brighter the star.  By measuring the star's variability period, an astronomer can know its true brightness.  The astronomer can then ascertain the star's distance by comparing its true brightness to its apparent brightness.    

We know that our Milky Way Galaxy maps thus far have been skeletal: revealing only the largest structures with this complex island Universe.    Through use of the Gaia satellite,  the ESA and its team of collaborators intend to produce a cartographic masterpiece: a highly detailed three dimensional map of our home galaxy.   Moreover, this map will show how the galaxy has evolved and how it will change over long spans of time.      It might even show us precisely where our solar system took form and where its been traveling over these few billion years.

We told you it was beyond exciting

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FROM THE CATACOMBS OF INFINITE KNOWLEDGE
All the water on Earth

We just had to share this image from the wonderful APOD (Astronomy picture of the Day.  www.apod.nasa.gov/apod/ )  It shows how much water exists on Earth's surface.   It isn't as much as one would think.  If the water were removed from Earth's surface and gathered together, it would form a sphere smaller than our own moon!.  Its diameter would be only about 700 kilometers.

​If all the water on Earth's surface were removed to form a sphere.  Image: Jack Cook and Adam Nieman 

This sphere does not include the substantial water reserves that might exist below the surface.      We thank DA subscriber Robert D for sending this image to us

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