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
              "The true mystery of the world is the visible, not the
invisible."
                                                        -Oscar Wilde


*THE DAILY ASTRONOMER*
*Monday, May 9, 2016*
*Monday's Mercurian Transit*

___________________________________________________________
SEE THE TRANSIT OF MERCURY AT THE SOUTHWORTH PLANETARIUM!
Telescopes will be available on Monday, May 9th between 7:13 a.m. - 2:41
p.m.
Safely observe the passage of Mercury across the Sun.
For more information, visit our web site    www.usm.maine.edu/planet
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Last week, we sent Monday's DA in advance.   This week, we shall send
Monday's article ahead of time again, as it pertains to Monday's transit of
Mercury.   If we waited until noon time on Monday to post this disaster,
the transit would already be more than half over.    Now, we understand
that some subscribers have grown weary of this incessant transit talk.   If
you are one of these beleaguered souls, take solace:  the next transit of
Mercury won't occur until November 2019!   You'll enjoy a three year
respite from transit mania.

We're just going to quickly go over the main points of this event and, of
course, will resort to our beloved question/answer format.

For more information about this event, please consult our "Transit of
Mercury" module:
http://usm.maine.edu/planet/da-april-11-2016-mercurian-transit-module


WHEN WILL IT BEGIN?  WHEN WILL IT END?
We will re-post the contact times and definitions:
NOTE:  The diagram we included below shows the different contact points.
However, during this transit, Mercury's path will be descending, not
ascending.

*CONTACT I:                        7:13:29 a.m.               (Sun's
altitude:  18.5o  )*

*CONTACT II:                      7:16:41 a.m.               (Sun's
altitude: 19.0o)*

*GREATEST TRANSIT:      10:57:46 a.m.             (Sun's altitude:  56.5o)*

*CONTACT III :                    2:38:05 p.m.             (Sun's altitude:
53.6o)*

*CONTACT IV:                     2:41:17 p.m.              (Sun's
altitude:  53.2o)*



*(Calculations courtesy of the US Naval Observatory.)*



*I:  Contact I*:  when Mercury is externally tangent to the Sun.  In other
words, the moment just before Mercury first appears against the Sun.
Contact I is also called the "external ingress"   The transit begins.
Relative to Earth's center, the transit begins at 11:12:19 UT (7:12:19 a.m.
EDT)   For Portland, Contact I begins at 7:13:29 a.m.



*II:  Contact II:*  the moment when all of Mercury first appears against
the Sun.  Or, the moment when Mercury is internally tangent to the Sun.
Relative to Earth's center, Contact II occurs at 11:15:31 UT (7:15:31 EDT)
For Portland, Contact II begins at 7:16:41 a.m.



*GREATEST TRANSIT:* the moment when the distance separating Mercury and the
Sun's center is a minimum.   Relative to Earth's centrer, the moment of
greatest transit is 14:57:26 UT (10:57:26 EDT).  For Portland, the moment
of greatest transit is 10:57:46 a.m.



*III:  Contact III:*  the last moment when all of Mercury appears against
the Sun.   Or, the moment when Mercury when internally tangent to the Sun.
Relative to Earth's center, Contact III occurs at 18:39:14 UT  (2:39:14
EDT)  For Portland, Contact III begins at 2:38:05 p.m.



*IV:  Contact IV:  *the planet's disk is externally tangent to the Sun.
The transit ends.   Relative to Earth's center, Contact IV occurs at
18:42:26 UT (2:42:26 EDT)  For Portland, Contact IV begins at 2:41:17 p.m.




*​This diagram shows the positions of contact points 1, 2, 3, 4.  Note that
during this transit, Mercury will appear to move along a descending path.*
*(Image courtesy of the Astronomical Almanac.)*


*WILL I SEE IT WITH THE UNAIDED EYE?*No.   It is only visible with a
telescope...or, one can make a homemade solar viewer.

Find a large cardboard box.     Cut a hole at one of the two shorter
ends.   Tape aluminum foil over this hole. Puncture the foil with a tack so
as to produce a very small hole. Tape a piece of white paper on the inside
of the box's other end. You would then place the box over your head with
the foil end facing the Sun.     An image of the Sun will be projected onto
the white paper.
By using this viewer, one can safely observe the transit.  The projection
will magnify the Mercury "dot" sufficiently so as to render it visible to
the unaided eye.  Of course, this dot will still be small.

*THE NEXT TRANSIT OF MERCURY WILL BE IN NOVEMBER 2019.  WILL WE SEE THAT
EVENT?*
Good news for those people who might miss Monday's transit.    Observers in
eastern North America will be able to see the Mercurian transit on November
11, 2019! The Daily Astronomer will be there to hype the event beyond all
proportion.


If nothing else, watching a Mercurian transit affords us an opportunity to
observe a planet in motion.    When seen in the night sky, a planet seems
stationary, even though it moves against the backdrop of stars.    This
motion is only observable by noting a planet's changing position from night
to night.  While one won't see Mercury literally moving during this
transit, its position will change so rapidly that one can note it even over
a few minutes: direct verification -as though we needed it- that the
planets indeed revolve around the Sun, not Earth.