Archive

Archive for the ‘Equinox’ Category

03/20/2020 – Ephemeris – The first full day of spring

March 20, 2020 Comments off

Ephemeris for Friday, March 20th. Today the Sun will be up for 12 hours and 11 minutes, setting at 7:55, and it will rise tomorrow at 7:43. The Moon, half way from last quarter to new, will rise at 7:00 tomorrow morning.

Spring snuck up on us at 11:50 p.m. last night, so this is the first full day of spring. That point in time and the point in the sky where the Sun crossed the celestial equator the imaginary line in the sky above the Earth’s equator heading northward is called the vernal equinox. Vernal means spring and equinox means equal night, meaning that day and night are equal. Since western civilization has spread south of the equator where seasons are reversed, our northern hemisphere spring equinox is the southern hemisphere’s autumnal equinox, so to be fair to both hemispheres we generally say March or September equinox instead. However the point in the sky the Sun crossed last night will always be known as the vernal equinox.

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

Addendum

Sun at the vernal equinox

The Sun at the vernal equinox point on the celestial sphere at 11;50 p.m. EDT last night (March 19, 2020). The diagonal yellow line in the ecliptic, the Sun’s path in the sky. The vertical lines marked in hours at the top are lines of right ascension, the analog of earthly longitude. The horizontal lines are lines of declination, the same as latitude on the Earth. I referenced this point in yesterday’s program. Created using Cartes du Ciel *Sky Charts).

Sun's path through the sky on the equinox

The Sun’s path through the sky on the equinox day from Traverse City, MI. Note that the Sun rises due east and sets due west. Created using my LookingUp program.

09/23/2019 – Ephemeris – Fall has fallen upon us

September 23, 2019 Comments off

Ephemeris for Monday, September 23rd. Today the Sun will be up for 12 hours and 7 minutes, setting at 7:38, and it will rise tomorrow at 7:32. The Moon, 2 days past last quarter, will rise at 2:01 tomorrow morning.

Fall has, well… fallen upon us and in a few weeks so will the leaves. At 3:49 (7:49 UT) this morning the Sun crossed overhead at the Earth’s equator heading south. At that same time the Sun theoretically set at the north pole and rose at the south pole. The day is called the autumnal equinox and the daylight hours today is 12 hours and 7 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 for us north of the equator 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.

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

Addendum

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.

Sunrise on the autumnal equinox

That is not a pumpkin on the head of the motorcyclist. That’s the Sun rising as I’m traveling east on South Airport Road south of Traverse City Mi. on the autumnal equinox. This is the east-west section of the road. The Sun is rising over the hills some 6 miles to the east. Credit: Bob Moler.

Categories: Ephemeris Program, Equinox, Seasons Tags:

03/21/2019 – Ephemeris – Are day and night really equal at the equinoxes?

March 21, 2019 Comments off

Ephemeris for Thursday, March 21st. Today the Sun will be up for 12 hours and 11 minutes, setting at 7:56, and it will rise tomorrow at 7:42. The Moon, 1 day past full, will rise at 8:52 this evening.

What we had yesterday was the vernal equinox, the start of spring. The word equinox means “equal night”. Yesterday’s daylight hours were 12 hours and 8 minutes. What’s with the 8 minutes? The rising or setting Sun is a mirage. The Earth’s atmosphere acts like a lens and makes the Sun appear higher in the sky than when it is when near the horizon. When the bottom edge of the Sun touches the horizon the Sun is actually still completely below the horizon geometrically. If the Earth had no atmosphere sunrises would occur 4 minutes later, and sunsets would occur 4 minutes earlier around here. That would completely correct the 12 hour 8 minutes daylight time of yesterday to 12 hours even.

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

Addendum

Atmospheric Refraction

How the atmosphere bends the light of the Sun or Moon rising or setting to appear higher than it actually is. Credit Francisco Javier Blanco González, 2017.

I took a look at the related atmospheric refraction effect last month: https://bobmoler.wordpress.com/2019/02/19/02-19-2019-ephemeris-the-moon-aint-just-super-near-the-horizon/.

 

03/19/2019 – Ephemeris – Spring and a super-moon happen tomorrow

March 19, 2019 Comments off

Ephemeris for Tuesday, March 19th. Today the Sun will be up for 12 hours and 5 minutes, setting at 7:53, and it will rise tomorrow at 7:46. The Moon, 1 day before full, will set at 7:55 tomorrow morning.

Today and tomorrow are busy days, astronomically speaking, for the Earth, Sun and Moon. This afternoon at 3:47 the Moon will reach the perigee point in its orbit of the Earth, its closest point of 223,200 miles (359,400 km) center to center. With the full moon just 30 hours later this will make the Moon a super-moon, the third in a row. The Moon will be full enough to call tonight’s moon a super-moon too when it rises around 6:16 p.m. The next event will be the coming of spring, when the Sun appears to cross the celestial equator heading northward. For a point in the Pacific Ocean, on the equator the Sun will be directly overhead at 5:58 p.m. our time or 21 hours, 58 minutes Universal Time or Greenwich Mean Time.

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

Addendum

Mini Moon and Super Moon

Mini Moon and Super Moon for 2017. Trouble is the Moon appears alone with nothing to compare it to when it is seen in the sky. Created using Cartes du Ciel (Sky Charts).

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. (This is from a couple of years ago. The actual length of daylight depends on when during the day the moment of the equinox occurs.  I’ll have more on that Thursday.)

09/20/2018 – Autumn will fall on us Saturday night

September 20, 2018 Comments off

Ephemeris for Thursday, September 20th. The Sun will rise at 7:27. It’ll be up for 12 hours and 16 minutes, setting at 7:43. The Moon, half way from first quarter to full, will set at 3:44 tomorrow morning.

Welcome to the last few days of summer. The weather has stayed summery thus far through September. The Sun will reach the autumnal equinox point in the sky at 9:54 Saturday evening. At that moment the Sun will cross the celestial equator, a projection of the Earth’s equator, heading southward. All locations on the Earth except two will experience 12 hours of daylight and 12 hours of night. Well they would if the Earth didn’t have an atmosphere and sunset and sunrise were defined differently. The two locations that don’t experience equal night, which is what equinox means, are the north pole where the Sun will be setting and the south pole where the Sun will be rising. For us in the northern hemisphere daylight hours will be shorter and the Sun will peak lower in the south each day until the December solstice.

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

Sun's path through the sky on the equinox
The Sun’s path through the sky on the equinox day from Traverse City, MI.  Local noon, when the Sun is due south, is 1:35 p.m. EDT.   Created using my LookingUp program.

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.

 

 

 

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.