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
            "Success is not final, failure is not fatal: it is the courage
to continue that counts."
                          -Winston Churchill




*THE DAILY ASTRONOMER*

*Wednesday, May 25, 2016*
*Whirlpool in the Sky*


We return to our May Messier frolic, during which we spare a few precious
moments to admire some of May's prominent Messier objects.   Messier*
objects, denoted by a capital M followed by a number specifying their
placement on the list, are celestial objects that resemble comets. These
objects include nebulae, galaxies, and star clusters.     French astronomer
Charles Messier (1730-1817) compiled a catalog of these bodies for the
benefit of other comet-hunting astronomers.     Although he didn't discover
all the bodies included in this catalog, they are all now categorized as
"Messier Objects."

Today's Messier frolic brings us to the famous "Whirlpool Galaxy"


Thirty seven million light years from Earth one finds the beguilingly
beautiful Whirlpool Galaxy.   Here one can behold a nearly perfect example
of a pure spiral galaxy, in which spiral arms curl away from a spherical
center so as to lend the entire structure both a vertical and horizontal
symmetry. Astronomers believe that the galaxy's current symmetry is a
result of its interaction with it companion galaxy, NGC 5195. Were one to
observe our own beloved Milky Way from a distance, one would note that the
center is barred, not spherical.)  Though it contains more than 100 billion
stars, the Whirlpool Galaxy is only about 45,000 light years in diameter,
less than half the estimated size of the Milky Way.     This size is
derived directly from the galaxy's angular dimensions and distance,
recently measured at 23 million light years.


*The Whirlpool Galaxy, or M51, is a beautiful spiral galaxy about 23
million light years from our solar system.  We observe the Whirlpool and
its companion NGC5195,  a smaller galaxy that  *
*will soon become incorporated into M51.   (Image:  National Optical
Astronomy Observatory)*
​

When Charles Messier first observed this galaxy in 1773, he discerned very
few features and actually described it as a faint nebula devoid of stars.
However, in 1845, astronomer Lord Rosse (1800-1867) discerned its spiral
structure.   It was the first instance in which such spirals were observed
in nebula.  However, these nebulae were still then believed to have been
intergalactic objects.   Only in the early twentieth century did Edwin
Hubble establish that many of the objects once perceived to have been
inside the Milky Way were actually far outside of it.

We now know that the Universe harbors an abundance of galaxies, the
population of which might even exceed the number of stars within our own
Milky Way.    While we cannot see our home galaxy from an external
viewpoint, we can observe other galaxies and from observations of their
structures infer the design of the Milky Way.   The Whirlpool provides us
with a very nice, though not precisely accurate, reflection of our own
island Universe.



*During the DA school year that begins on September 1, 2016 and ends August
4, 2017, we intend to visit every single Messier, as 2017 will mark the
200th anniversary of Charles Messier's death.