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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