Saturday, May 05, 2012

Lunation Lunacy

Zebulon, NC

Tonight's perigenal full moon was in the news today.

Do I seem obsessed by lunation phenomona?  If so, that is because it's true.  I think it is great fun to see the wonders of nature in a way that science and mathematics predict so accurately.

Spring tides are extra high/extra low tides that occur when the moon and the sun are aligned (new moon) or opposed (full moon).   When sun and moon are 90 degrees out of phase, we have neap tides.  Actually, spring tides happen a couple of days after new/full moons because of local effects.

Below, you see the tides for 30 days at Bridgeport, Connecticut.  The spring/neap tide variations are very plain.

The moon's orbit is not circular.  It is closest ad perigee and furthest at apogee.  The biggest spring tides occur when full or new moon correspond to perigee.  They are called perginal spring tides.  Below you see the tides at Bridgeport, Connecticut for a period of 400 days.  At that scale you not only see the spring tide cycles, but the variations in spring tide levels and thus the perigenal spring tides.  Cool huh?

Regular readers also know that I've written several times about perfect moonrises.  I define a perfect moonrise as being the time when the moon rises in exact syncronism as the sun sets.  That happens, of course, on the evenings of full moons.  However, at the moment of full moon, there is only one longitude on earth where the moon is rising at that exact minute.  The coincidence of that date, time and longitude give you the time and place of the perfect moonrise.  I calculated those dates, times and longitudes for the next several years.  See the table below.

--Date----- -Latitude- --Approximate Place-- 

2012 May  6       054W Suriname
2012 Jun  4       168W American Somoa
2012 Jul  3       077E New Delhi, India
2012 Aug  2       052W Cayenne, French Guiana
2012 Aug 31       151E Sydney, Australia
2012 Sep 30       050W Sao Paulo, Brazil
2012 Oct 29       062E Western Afganistan
2012 Nov 28       138E Papua, New Guinea
2012 Dec 28       156W Hawaii
2013 Jan 27       070W Buzzards Bay, Rhode Island, USA
2013 Feb 25       053E The Caspian Sea
2013 Mar 27       143W Chugach Mountains, Alaska, USA
2013 Apr 25       060E Ural Mountains, Russia 
2013 May 25       067W Bar Harbor, Maine, USA
2013 Jun 23       174W Aukland, New Zealand
2013 Jul 22       086E Kathmandu, Nepal
2013 Aug 21       026W Thule, Greenland
2013 Sep 19       168W Midway Island, Pacfic
2013 Oct 18       006E Luxembourg
2013 Nov 17       131E Kyusu, Japan
2013 Dec 17       142W Marquesas Island, Pacfic
2014 Jan 16       074W New York City
2014 Feb 14       001E London, England
2014 Mar 16       102E Bangkok, Thailand
2014 Apr 15       116W Las Vegas, Nevada, USA
2014 May 14       070E Kabul, Afganistan
2014 Jun 13       064W Virgin Islands, Atlantic
2014 Jul 12       172W Midway Islands, Pacfic
2014 Aug 10       087E Rangpur, India
2014 Sep  9       025W Azores Islands, Atlantic
2014 Oct  8       163W Aleutian Islands, Bering Sea
2014 Nov  6       024E Athens, Greece
2014 Dec  6       173E Midway Islands, Pacific
2015 Jan  5       074W New York City
2015 Feb  3       013E Rome, Italy
2015 Mar  5       088E Dhaka, Bangaladesh
2015 Apr  4       178E Fiji, Pacific
2015 May  4       056W Buenas Aires, Argentina
2015 Jun  2       115E Hong Kong
2015 Jul  2       036W Mouth of the Amazon River, Brazil
2015 Jul 31       162W Nome, Alaska, USA
2015 Aug 29       081E Sri Lanka
2015 Sep 28       043W Rio De Janerio, Brazil
2015 Oct 27       179E International Date Line, Pacific
2015 Nov 25       019E Budapest, Hungary
2015 Dec 25       168W Niue Islands, Pacific

Unfortunately for me, none of those are the time and place where I'm likely to be.  In fact, for a given longitude, one gets to see a perfect moonrise only once every 30 years.  A perfect perigean moonrise happens once every 225 years at a given longitude.  Therefore, the chances of seeing any of these events is very rare unless you are willing to travel to the given longitude to see it.

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