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:  2457681.16
             "Nestled in night's smallest hollows."

*THE DAILY ASTRONOMER*
*Tuesday, October 18, 2016*
*Double Pandora*

It's like being a young, immortal fool and your mother's commanding you to
clean your room sometime before the Sun goes supernova, for Heaven's sake!
  And, by the time you start explaining that the Sun isn't nearly massive
enough to go......the door slams and you're left in isolation.  As you look
ruefully toward the door and miserably around at the contained catastrophe
that only a workaholic microbiologist would like, you think that you have
plenty of time to comply with the "request."     Then, almost the next day,
the Sun expands to a red giant and as the layers approach the incinerating
Earth,you hear, "So, how's that room?!"  And, before you can explain that
what the Sun is experiencing isn't a supernova so you still have time, a
stern woman is surveying your room with disgust and then surveying you with
reproach....

Hence, our hundred-question Pandora pledge.    We're only on parchment
number 4 and it is already mid October.  We have to have the hundredth
parchment pressed and addressed by early August, which seems like it is a
century and a half  in the future, but will likely smack us broadsides as
we walk through our gallery next week.  (When one works in a dark
planetarium, one experiences these temporal assaults from the past and
future so often they become all too commonplace.)     We have to curb this
tendency to procrastinate (not that we're doing that now) and get on with
it.

So, we're getting on with it.


*Pandora Parchment # 4:   The moon is tidally locked with Earth so that it
keeps the same face toward the planet.  I heard that eventually there will
be a mutual tidal lock so that the Earth's rotation and the the moon
revolution will be the same.  When will this happen?   -N.B,   Freeport*

You are correct that the moon and Earth will eventually achieve a mutual
tidal lock, just as Pluto and Charon have done.    However, this is not due
to happen for about 50 billion years!    The Sun will have ended its life
cycle well before the moon and Earth reach this stage.     To provide some
background:    The moon's rotation period equals its revolutionary period
so that the moon directs its same side toward Earth.    Meanwhile, as the
moon revolves around Earth, it induces a "bulge" that is not exactly
aligned with the Earth moon line due to Earth's rotation.    The moon pulls
on this bulge and the bulge pushes on the moon.    As a consequence of the
former, Earth's rotation slows down slightly: by less than a millionth of a
second each year.   (Those harassed workers who wish there were 25 hours in
a day need only wait 140 million years for this to be true.)       As a
consequence of the latter, the moon gains a bit of energy, its orbit widens
and it slowly recedes from us by a few centimeters per year.
However, the rate is so slow that the moon and Earth will not even come
close to achieving complete tidal lock before the Sun's life cycle ends

*Pandora Parchment # 5:  How do we know the Sun rotates and is it true that
the pole rotates at a different speed than the equator?   -P. Spencer,
 Bath*

The famous Italian astronomer Galileo Galilei (1564-1642) was the first
person to have observed and recorded spots on the Sun,   Curiously, we
refer to these splotches now as "sunspots."   Galileo observed that these
spots migrated across the Sun, which was indicative of rotational motion.
Moreover, this rotation time varies because the Sun is not a solid body,
but is instead a fluid, or, more correctly a "plasma."

If the Sun didn't have spots, we would have been hard pressed to have known
about its rotation.   Galileo suffered the consequences of his
observations, however, as he observed the Sun through his small telescope
without any protection.     During the last years of his life, Galileo was
stone blind.



​*Rotating Sun.    The Sun rotates on its axis.  However, because it is a
"fluid," it experiences differential rotation.  The Sun's equatorial
rotation rate is once every 27 Earth days, but its polar rotation is 35
Earth days.  The rotation rate increases with ascending solar latitude.
Image: Weather.gov*


*_____________________________________________________________*
*FROM THE CATACOMBS OF INFINITE KNOWLEDGE*
*How fast are you moving, Earthling?*

Unlike the Sun, Earth rotates as a solid body.   However, the speed of
rotation still varies with latitude because the circumference of any
latitude circle, itself, is variable.  It is maximum on the Equator and
minimum at the poles.  The Earth is nearly -though not exactly- spherical.
Consequently, the distance around Earth decreases as one moves away from
the Equator.   Since every point on Earth completes a rotation at the same
time as any other point, the rotation rate is determined by the size of the
circle at a given latitude.     A person standing on the equator travels
more during one rotation than a person at a higher latitude, so the
equatorial inhabitant has to travel faster.

It is the exact same notion as a spinning record!    (Refer to the comic
strip below the map.)



*​*
*Earth's rotation speed.        How fast are you moving on this rotating
Earth?  The answer depends on your location.   People on the equator are
moving at 1040 miles per hour.   However, someone standing on the Arctic
Circle (66.5 degrees N) is moving at only 414 miles per hour.  The chart
above shows the varying rotational speeds at different latitudes.    Image:
Seth Kadish*

NASA launches rockets from the southern part of the United States because
Earth is rotating faster there than at any other part of the country.
NASA engineers, typically clever folks, have figured out how to impart a
greater boost on these rockets due to the higher rotation speed.



*​Calvin and Hobbes    by Bill Watterson*