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Archive for the ‘Equinox’ Category

04/14/2014 – Ephemeris – Why does Easter occur on a different Sunday every year?

April 14, 2017 Comments off

The answer is astronomical!

Ephemeris for Good Friday, Friday, April 14th.  The Sun will rise at 6:59.  It’ll be up for 13 hours and 26 minutes, setting at 8:26.  The Moon, 3 days past full, will rise at 11:48 this evening.

Easter will be celebrated by western and eastern christian churches this Sunday.  Easter is a movable feast in that it falls on a different date each year following the first full moon of spring.  It’s an attempt to follow the Jewish Passover, which starts on the 15th of the month of Nisan.  Being a lunar calendar the 15th the generally the night of the full moon.  And since the Last Supper was a Seder, the Christian church wanted to follow Passover as closely as possible using the Roman solar based calendar where the year was 365.25 days long.  Passover started at sunset this past Monday night.  The western churches eventually adopted the Gregorian calendar to keep in sync with the seasons.  The Eastern churches did not, however Easter is late enough this year so they both fall on the same date.

The times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

The seasonal, or officially the Tropical Year, from vernal equinox to vernal equinox is approximately 365.24220 days long, about 11 1/2 minutes shorter than the Julian (after Julius Caesar) Calendar year.  The Julian Calendar kept up with the year by having three 365 ordinary years and one leap year of 366 days.  It over corrects.  To make the calculation for Easter easier in the various dioceses of the far-flung church, the vernal equinox, the day the Sun crosses the celestial equator, heading northward was defined as March 21st.  The actual vernal equinox was falling behind the Julian Calendar by 0.8 days every century.

By 1582 the Roman Catholic Church under Pope Gregory XIII decided to correct the problem.  By then the real vernal equinox occurred on March 11th.  Easter is supposed to be a spring feast, and using March 21st as the vernal equinox would eventually push Easter into summer.  The Pope instituted a commission to look into the problem.  This commission headed by Christophorus Clavius* came up with what we know as the Gregorian Calendar.  First, eliminate 10 days from the calendar.  This was done in October 1582 between October 4th and 15th.  Then to keep the calendar in sync with the actual year it was decreed that leap years would continued for years divisible by 4; except that century years, those divisible by 100 be ordinary years, except those by also divisible by 400.  Thus the year 1900 was an ordinary year, but the year 2000 was a leap year, and the year 2100 will be an ordinary year.  Adoption of this as a civil calendar took 400 years to be universal.

The Greek Orthodox and other eastern churches kept the Julian Calendar, so on occasion their Easter is sometimes celebrated in May.  The Jewish Calendar is, as I alluded to in the program transcript, a lunar calendar.  It has a relationship to the Julian Calendar in that 19 Julian Years equals 235 lunar months almost exactly. This is called the Metonic Cycle.  Those 235 months equal 12 lunar years of 12 and 13 months.  So without correction Passover too will slowly head into summer in millennia to come.

* Clavius was honored by having a large, rather spectacular crater on the Moon named for him.  Search these posts for Clavius to find it.

 

 

 

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03/20/2017 – Ephemeris – Spring starts today!

March 20, 2017 Comments off

Ephemeris for Monday, March 20th.  The Sun will rise at 7:45.  It’ll be up for 12 hours and 10 minutes, setting at 7:55.  The Moon, at last quarter today, will rise at 3:39 tomorrow morning.

This morning, at 6:29 (10:29 UT) the sun crosses overhead at the earth’s equator as it appears to head north, starting for us the season of spring.  It’s the vernal equinox.  As you can tell from my intro, we’re already above 12 hours of daylight, and we’ll add another 3 plus hours of daylight before summer begins in three months.  We are already adding about 3 minutes a day of daylight to that goal now, the maximum rate.  With the Sun out longer and its ascension higher in the sky each day, it is rapidly adding energy to the northern hemisphere.  We don’t feel that immediately.  While the land rapidly absorbs heat, the oceans and lakes, especially the Great Lakes are a big heat sink, taking a very long time to warm up.

Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

This March equinox also is the beginning of autumn for folks south of the equator.

Earth near equinox

Image from the DISCOVR satellite in halo orbit at the Earth-Sun L1 point, nearly a million miles (1.6 million km) sunward of the Earth. as of March 17, 2017. As usual Michigan is covered by a cloud.  Credit NOAA/NASA.

11/24/2016 – Ephemeris – The little constellation that used to start the seasonal year

November 24, 2016 Comments off

Ephemeris for Thanksgiving Day, Thursday, November 24th.  The Sun will rise at 7:52.  It’ll be up for 9 hours and 14 minutes, setting at 5:06.  The Moon, 3 days past last quarter, will rise at 3:54 tomorrow morning.

From antiquity, the first constellation of the Zodiac has been Aries the ram.  That’s the constellation the Sun entered on the first day of spring, or the vernal equinox.  Well that was a couple of thousand years ago.  Currently the vernal equinox point is in western Pisces.  This is due to the wobbling of the Earth’s axis called precession.  The spinning Earth like and top or gyroscope wobbles when force is applied to it.  In this case the Sun and Moon.  One wobble takes 26,000 years to complete.  Anyway, Aries is a small constellation of four stars in a bent line, below the triangular constellation of Triangulum, which is itself below Andromeda.  It’s a bit west or right of the Pleiades or Seven Sisters star cluster.

Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

Aries the ram

Aries the ram animated finder chart for 9 p.m. November 24, 2016. Created using Stellarium and GIMP.

The vernal equinox today

The vernal equinox today, where the blue line, the celestial equator and the orange line, the ecliptic or path of the Sun cross. The Sun is where these lines cross on the first day of spring (March 20th around here). Note that the vernal equinox is now in western Pisces. Created using Stellarium.

The vernal equinox in AD 100

The vernal equinox back in AD 100, where the blue line, the celestial equator and the orange line, the ecliptic or path of the Sun cross. The Sun is where these lines cross on the first day of spring. Note that the vernal equinox was at the east edge of Pisces. Created using Stellarium.

09/22/2016 – Ephemeris – Autumn will begin this morning

September 22, 2016 Comments off

Ephemeris for Thursday, September 22nd.  The Sun will rise at 7:30.  It’ll be up for 12 hours and 8 minutes, setting at 7:39.  The Moon, 1 day before last quarter, will rise at 12:06 tomorrow morning.

Fall is about to a, well… fall upon us and in a few weeks so will the leaves.  At 10:21 (14:21 UT) this morning the Sun will cross the celestial equator heading south.  The celestial equator is an imaginary line in the sky above the earth’s equator.  At that point the sun will theoretically set at the north pole and rise at the south pole.  The day is called the autumnal equinox and the daylight hours today is 12 hours and 8 minutes instead of 12 hours exactly.  That’s due to our atmosphere and our definition of sunrise and sunset.  The reason for the cooler weather now and the cold weather this winter is that the length of daylight is shortening, and the Sun rides lower in the sky, spreading its heat over a larger area, thus diluting its intensity.

Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

The Earth near the autumnal equinox

The Earth as seen a couple of days ago from NOAA,s DSCOVR satellite located near the Sun-Earth L-1 point 1 million miles sunward from the Earth. Credit NOAA/NASA.

Sun's path through the sky on the equinox

The Sun’s path through the sky on the equinox day from Traverse City, MI. Created using my LookingUp program.

 

09/16/2016 – Ephemeris – The Harvest Moon is slightly eclipsed for everyone but the Americas

September 16, 2016 Comments off

Ephemeris for Friday, September 16th.  The Sun will rise at 7:23.  It’ll be up for 12 hours and 27 minutes, setting at 7:50.  The Moon, at full today, will rise at 7:59 this evening.

Tonight’s full Moon is the Harvest Moon, the nearest full Moon to the autumnal equinox.  For the next few nights the Moon will rise later each night by much less than the average 50 minutes later each night effectively lengthening twilight for those gathering in crops.  Also this afternoon there will be a penumbral lunar eclipse visible, well not here in Michigan… because the Moon won’t be up.   Actually just about the whole world except North America and most of South America will be able to see the eclipse.  A penumbral eclipse is what I call a 5 o’clock shadow eclipse.  You wouldn’t know it unless someone pointed it out to you, when the Moon dips into the Earth’s outer shadow and the sunlight falling part of it is diminished by a little bit.

Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

Moonlight on the bay

The not so full Moon of Monday night and its reflection on the waters of Suttons Bay after the schooner Inland Seas docked after an evening sail. Credit: the author.

Penumbral eclipse 9/16/2016

The penumbral eclipse of the Moon centered on 2:25 p.m. Eastern time, 18:54 UT, for an hour and a half before and after. Only near the middle of the eclipse will anything be visible of the effect. I find that wearing sunglasses reduces the brightness of the moon and enhances the penumbral shadow. Credit: NASA/GSFC/ Fred Espenak.

For the full-page pdf of the above click here: http://eclipse.gsfc.nasa.gov/LEplot/LEplot2001/LE2016Sep16N.pdf

09/13/2016 – Ephemeris

September 13, 2016 Comments off

Ephemeris for Tuesday, September 13th.  The Sun will rise at 7:19.  It’ll be up for 12 hours and 36 minutes, setting at 7:56.  The Moon, 3 days before full, will set at 4:40 tomorrow morning.

Last Thursday evening an Atlas V rocket lifted off with NASA’s only interplanetary mission this year.  The spacecraft called by one of NASA’s tortured acronyms OSIRIS-Rex is on its way to the asteroid Bennu, which was discovered in 1999, and named by a 3rd grader in a contest.  Bennu is an Egyptian deity resembling a heron and also resembling the spacecraft.  OSIRIS-Rex will take two years to reach the small asteroid, orbit it for two years mapping it in great detail and will approach to retrieve a sample.  It will take 3 years to return the sample to the Earth in 2023.  Bennu is interesting because it contains organic compounds from the origin of the solar system and because of the tiny chance it could hit the Earth in 200 years or so.

Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

OSIRIS-REXx

The OSIRIS-REx spacecraft with its sampler boom extended.

Categories: Asteroid, Equinox, NASA

09/22/2015 – Ephemeris – Equinox tomorrow and September 27th Moon’s triple whammy

September 22, 2015 Comments off

Ephemeris for Tuesday, September 22nd.  The Sun will rise at 7:29.  It’ll be up for 12 hours and 11 minutes, setting at 7:40.   The Moon, 1 day past first quarter, will set at 2:02 tomorrow morning.

Tomorrow at 4:20 a.m. before most of us wake up summer will officially end and Autumn will start.  That’s the exact time of the autumnal equinox.  We are noticing that the days or rather daylight hours are getting noticeably shorter day by day.  Autumn will end when the days will stop getting shorter on the first day of winter, December 21st.  The full moon this Sunday is triply important.  Most important is that a total lunar eclipse will happen.  Second, it is the Harvest Moon, the nearest full moon to the autumnal equinox, more on that next week.  Also it is the closest the Moon gets to the Earth all year.  Yup it’s a so-called supermoon.  If the Moon were a 2 inch ball it would be 20 feet from an 8 inch Earth.  The supermoon is a foot closer.

Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

That last bit about the Moon being a two-inch ball will come in handy if you come to the Girl Scout Badge Bash at ECCO in Traverse City Thursday night.