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
            "Heavens above!"



*THE DAILY ASTRONOMER*

*Tuesday, June 21, 2016*
*Solstie**e **Que*
*ries*

To be honest, today's article has nothing to do with Pandora.    We
visited that
jar so often last week we thought it prudent to give it a miss for a few
days.  Instead, we decided to compile a brief list of questions pertaining
to the summer solstice.   We've received this queries throughout the years
from subscribers and planetarium patrons.    Now that astronomical summer
has begun, there seems no better time to answer these questions.


*Is i**t true that summer is the longes**t season in the northern
hemisphere?*
Though it is difficult for northern climate dwellers to believe, summer is,
indeed, the longest of the four seasons.   Earth reaches aphelion (its
greatest distance from the Sun) on or around July 4th.   At this time, Earth's
orbital velocity is at a minimum. We remember that a planet's distance from
its parent star determines its orbital speed.   Greater distance reduces
the velocity.    So, Earth requires about 92 - 93 days to travel from the
summer solstice point to that of the autumnal equinox.    Conversely, Earth
is at perihelion (closest distance to the Sun) around January 3rd.
Consequently,
Earth needs only 88 - 89 days to move from the winter solstice point to
that of the vernal equinox.     Although winters here last a century and
seem intended to punish us for a trangression a remote ancestor perpetuated,
winter is the briefest of the four seasons.

*Why don't we experience t**he "mi**dnight sun" effect like some places **do
around the solstice?*
We're not far enough north or south.
On the summer solstice, any region just of the Arctic Circle* (66.5 degrees
N) will experience the 'midnight sun' effect.   This means that the Sun
will not set at these latitudes and will be visible for twenty four hours a
day.    On the winter (December) solstice, all regions south of the
Antarctic Circle (66.5 degrees S) will experience the midnight sun
effect.

These boundaries are constantly changing.  Now that the solstice is over,
the southern 'midnight sun' boundary will migrate north.     For instance,
on August 1, only observers north of 72 degrees N will have the midnight sun.
On the autumal equinox, a small region centered around the north pole will
have the midnight sun. (The sun would set at the north pole on the autumnal
equinox were it not for our atmosphere.)

*Why isn't the **summer solstice** on June 21st this year (2016)?*
The main reason is because of our calendar.  Our Gregorian calendar added a
leap day in February.  Had it not done so. the Sun would have reached the
summer solstice on June 21st.   Blame Pope Gregory XIII.

*Why did the** solstice Sun shift from Gemini into **Taurus?*
Because of precession.   Earth 'wobbles' just as gyroscope does when
rotating.
The Sun, Moon, and -to a lesser extent- the planets induce this wobble so
that the north pole describes a 47-degree circle over a 26,000 year time
period.  During this precessional period, the thirteen ecliptic constellations
(those that the Sun appears to occupy at different times throughout the year)
migrate to every part of the ecliptic.   For instance, the Sun once
occupied Cancer the Crab on the summer solstice.  (For this reason, the
latitude where the Sun passes directly overhead on the summer solstice is
called the "Tropic of Cancer.")  In the year 9 BC/BCE, the position of the
summer solstice shifted into Gemini the twins.  In 1989, this point moved
into Taurus. where will it remain until moving into Aries the Ram in 4609!
Even though precession is a gradual process, sometimes a seasonal point can
move into a different constellation during our lifetime.


*What season is it now on the Equator?*
As the Equator is not a region, but a line of no thickness, there is no
season on the Equator*.  *Let's pretend you are standing on the equator
facing west right now. The part of your body south of the equator is
experiencing winter, the part north of the equator is in summer.
Granted, you won't notice the difference.




*The boundary is just south of the Arctic Circle due to atmospheric refrac
tion.


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FROM THE CATACOMBS OF INFINITE KNOWLEDGE
A new day begins at midnight, but "daylight" begins when the top of the Sun
is first visible above the horizon.
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