THE SOUTHWORTH PLANETARIUM 207-780-4249   www.usm.maine.edu/planet
<http://www.google.com/url?q=http%3A%2F%2Fwww.usm.maine.edu%2Fplanet&sa=D&sntz=1&usg=AFQjCNHulkHuLP13bOG2PkNrPazsGWFs2A>
70 Falmouth Street   Portland, Maine 04103 43.6667° N
 70.2667° W  Altitude:  10 feet below sea level Founded January 1970 Julian
Date:  2459340.18
2020-2021: CXXIII


THE DAILY ASTRONOMER
Wednesday, May 5, 2021
Amazing Astronomy Facts

A immensely pleasant and preternaturally cheerful fellow asked me yesterday
to compile a list of what I consider to be amazing astronomy facts.  And,
because he is immensely pleasant and preternaturally cheerful, I was all
too happy to oblige.   Of course, this list turned out to be longer than I
initially intended it to be, so I divided it into two articles.


*LIGHT AND LIGHT YEAR*
Imagine you have a laser pointer so horrifyingly powerful that the beam
would wrap around the equator repeatedly. (Assume irrationally that the
beam will also not hit anything or anyone during these rapid
circumnavigations.)      That light beam could complete 7 1/2 revolutions
every single second.

Astronomers often measure stellar distances in light years,  defined as the
distance that a light beam, when moving through a vacuum, travels in one
Earth year, a distance approximately equal to 5.8 trillion miles.  Or,
think of the matter this way.   Please blink.   Splendid.  During the
moment when you blinked, immense amounts of light left the "surfaces" of
the three stars comprising the Alpha Centauri star system.  At a distance
of 4.3 light years, Alpha Centauri is the closest star to the Sun.   A
minuscule amount of the light the stars emitted when you blink will arrive
at Earth in 4.3 years.   For instance, I am writing this absurd paragraph
on May 5, 2021. The light that left Alpha Centauri when I blinked will
reach Earth in August, 2025!

Look at the Big Dipper:

[image: Fujii-Big-Dipper-Labeled_900x713_v2.jpg]
The five "central stars," Alcor/Mizar, Alioth, Megrez, Phecda, and Merak,
are all approximately 76 light years from Earth.   If you observe these
stars when you're 76, you'll be seeing them as they were the year you were
born.


*Regard the Andromeda Galaxy:*

[image: stargazingimage.webp]
The Andromeda Galaxy, the largest member of the Local Group, is the closest
major galaxy to the Milky Way.   Approximately 2.2 million light years from
the Milky Way, this spiral galaxy is the most distant celestial object
visible to the unaided eye.   From our perspective, it resembles a 4
degree-wide smudge of light within the constellation Andromeda, hence the
name.   When one looks at this galaxy, one will be seeing it as it was 2.2
million years ago, around the time when Homo Habilis, the first known
member of the genus Homo -the same genus to which we humans belong- first
evolved in east Africa.

[image: habilis_illustration_kc_head_p.jpg]
*Homo Habilis*


*SPEED*
Regard our dynamic world: in a constant state of flux and motion.    The
world comes by this ceaseless dynamism honestly as it is part of a Universe
that is never stagnant.

No matter where you are on Earth, you're standing on a rotating planet.
However, the closer one is to the equator, the faster the tangential
rotation speed will be.  For instance, a person on the equator moves around
the planet at 1036 miles per hour.     However, in southern Maine, one is
rotating at 757 miles per hour.    On the Arctic (or Antarctic) Circle, one
would rotate at 413 miles per hour.

[image: tumblr_mzv5b7Sljz1s3dn7vo1_1280.png]

Earth, itself, whips around the Sun at an average speed of 66,000 miles per
hour.*   The planet is moving more than eight times faster than a speeding
bullet!

Earth, the Sun and the rest of the solar system moves through the galaxy at
143 miles per second, equal to nearly half a million miles per hour.  Even
at this impressive speed, the solar system requires nearly 225 million
years to complete one circuit around the Milky Way Galaxy.


*NOT QUITE IMMORTAL CONSTELLATIONS*

All the stars within this region of the galaxy are moving at speeds
comparable to that of the Sun.  Consequently, the stars comprising the
constellations will gradually alter their positions to such an extent that
the constellations will eventually become unrecognizable.
In the graphic below, we see various images of the Big Dipper (top) and
Orion the Hunter (below).    The first panel shows both star patterns as
they appeared about 52000 years ago. The second panel depicts these
patterns as they appear today.  In the third and fourth panel, we see them
as they will appear in the distant future:

[image: 272B772D00000578-0-image-a-4_1427817090519.jpg]
Notice that the five "central" Big Dipper stars and the three stars
comprising Orion's Belt more or less maintain their positions relative to
each other because they are at approximately the same distance.from us.  In
fact, those five Big Dipper Stars are part of the Ursa Major Moving Cluster
and so will be moving together through space for quite some time.


More amazement tomorrow!






*Earth moves fastest when it is closest to the Sun in January and slowest
when it is farthest from the Sun in July.





To subscribe or unsubscribe from the Daily Astronomer:
https://lists.maine.edu/cgi-bin/wa?SUBED1=DAILY-ASTRONOMER&A=
<https://lists.maine.edu/cgi-bin/wa?SUBED1=DAILY-ASTRONOMER&A=1>