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12/21/2021 – Ephemeris – Winter starts today as the Sun starts coming back up north

December 21, 2021 Comments off

This is Ephemeris for Tuesday, December 21st. Today the Sun will be up for 8 hours and 48 minutes, setting at 5:05, and it will rise tomorrow at 8:17. The Moon, 3 days past full, will rise at 7:11 this evening.

The thermometer and snowfall tell us that winter ought to be here. Well, it will be at 10:59 this morning. At that point, the Sun will be directly over the Tropic of Capricorn at 23 ½ degrees south latitude. It’s an odd name because 2,000 years ago the Sun was in indeed entering Capricornus. Now it’s entering Sagittarius, right above the spout of the teapot asterism we know so well in summer. From then on the Sun will be climbing up the sky each noon until June 21st next year when summer will start. To which I say Go Sun Go! The Sun will almost make it up to 22 degrees above the southern horizon at local noon, which is 12:40 pm, in Interlochen and be out for only 8 hours and 48 minutes. If it stayed that low all year, we’d be in a deep freeze, possibly colder than Antarctica.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT – 5 hours). They may be different for your location.

Addendum

Solstices

Comparing the sun’s path at the summer and winter solstices in Traverse City, MI, located near 45 degrees north latitude. This is a stereographic representation of the whole sky, which distorts the sky and magnifies the size of the sun’s path near the horizon.

Earth's position at the solstices and equinoxes

Earth’s position at the solstices and equinoxes. This is a not to scale oblique look at the Earth’s orbit, which is nearly circular. The Earth is actually farthest from the Sun on July 4th, and closest on January 3, next year. Click on the image to enlarge. Credit: ESO (European Southern Observatory), which explains the captions in German and English.

Of course, the winter solstice for us is the summer solstice for folks in the Southern Hemisphere. Solstice is “Sun stand still”. The Sun has been  moving southward in the sky at noon since June, and today has stopped, and will now start heading northward again.

09/24/2021 – Ephemeris – Capricornus, home this season to Jupiter and Saturn

September 24, 2021 Comments off

This is Bob Moler with Ephemeris for Friday, September 24th. Today the Sun will be up for 12 hours and 3 minutes, setting at 7:35, and it will rise tomorrow at 7:33. The Moon, halfway from full to last quarter, will rise at 9:26 this evening.

Nearly 2000 years ago the southernmost of the constellations of the zodiac was Capricornus the water goat. That’s why the latitude on the Earth where the Sun is overhead on the winter solstice is called the Tropic of Capricorn. Not anymore, Sagittarius, one constellation west, has that honor today*. Capricornus is large, but made up of dim stars. To me, it looks like a 45 degree isosceles triangle, long side up, but which all the sides are sagging. The constellation is found low in the south at 10 to 11 p.m. The image that is supposed to be represented by the stars is that of a goat whose hind quarters are replaced by a fish’s tail, not a mermaid but a mer-goat. This autumn, Jupiter is at the left end of Capricornus, with Saturn on the right.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT-4 hours). They may be different for your location.

The reason for the shift is lunisolar precession, which I talked about yesterday.

Addendum

Capricornus w/Jupiter & Saturn finder animation

Capricornus w/Jupiter & Saturn finder animation for 10 pm, September 24, 2021. Created using Stellarium and GIMP.

12/20/2019 – Ephemeris – Winter arrives late tomorrow night

December 20, 2019 Comments off

Ephemeris for Friday, December 20th. Today the Sun will be up for 8 hours and 48 minutes, setting at 5:04, and it will rise tomorrow at 8:16. The Moon, 1 day past last quarter, will rise at 2:55 tomorrow morning.

Tomorrow will be the first day of winter, barely, since the moment of solstice will arrive at 11:19 p.m. If you’re south of the equator this is the first day of summer. The Earth reaches a point in its orbit where its north pole is tipped its furthest away from the Sun, and is in shadow in the middle of it’s six month night. The Sun for us is up only 8 hours, 48 minutes, and to boot the Sun only rises 22 degrees above the horizon giving us the least amount of energy of any day of the year. Why did the ancients celebrate this time of year? That’s because the Sun had slowed and stopped its drift southward and was beginning to come back higher in the sky. Spring and summer would eventually return!

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

Addendum

Winter solstice

The sun’s daily path through the sky from horizon to horizon on the first day of winter, the winter solstice. Credit My LookingUp program.

December solstice

The Earth and its axis on the first day of winter, the winter solstice. From my Sun and the Earth talk slides.

Solstice shadows

Comparison of shadows between winter and summer solstices. Note the angles are approximate.

12/21/2019 – Ephemeris – Winter starts today

December 21, 2018 Comments off

Ephemeris for Friday, December 21st. The Sun will rise at 8:16. It’ll be up for 8 hours and 48 minutes, setting at 5:05. The Moon, 1 day before full, will set at 7:56 tomorrow morning.

Today is the shortest day of the year, well in daylight hours. The Sun will be up for only 8 hours and 48 minutes in the Interlochen/Traverse City area, 8 hours 53 minutes in Ludington, and 8 hours 40 minutes at the Straits. This is because the northern end of the Earth’s axis is pointing some 23 and a half degrees away from the Sun. Or it will at 5:22 this afternoon, the instant of winter solstice, when winter will begin. To find how high the Sun will get in the south at local noon take 90 minus your latitude and subtract also 23 and a half degrees. For Interlochen that’s 21.8 degrees above the southern horizon. We’re not getting much heat from the Sun. But as winter progresses the rising Sun will slow the cooling and begin to warm us up before spring.

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

Addendum

December solstice

The Earth and its axis on the first day of winter, the winter solstice. From my Sun and the Earth talk slides.

The Earth near the December solsitce

DSCOVR satellite’s Earth Polychromatic Camera image of the Earth at 18:09 UTC (1:09 p.m.) December 19, 2017. We’re way up at the top just under the clouds at the top. It was actually partly cloudy that day. The DSCOVR satellite was in a halo orbit about the Earth-Sun Lagrange L1 point, 934,498 miles (1,503,929 km) toward the Sun from Earth.

Solstices

Comparing the sun’s path at the summer and winter solstices for Interlochen/Traverse City. This is a stereographic representation of the whole sky which distorts the sky and magnifies the size of the sun’s path near the horizon.

12/21/2017 – Ephemeris – Winter begins this morning

December 21, 2017 1 comment

Ephemeris for Thursday, December 21st. The Sun will rise at 8:16. It’ll be up for 8 hours and 48 minutes, setting at 5:05. The Moon, 3 days past new, will set at 8:23 this evening.

The thermometer and snowfall tell us that winter ought to be here. Well it will be at 11:29 this morning. At that point the Sun will be directly over the Tropic of Capricorn at 23 ½ degrees south latitude. Odd name because 2,000 years ago the Sun was in indeed entering Capricornus. Now it’s entering in Sagittarius, right above the spout of the teapot asterism we know so well in summer. From then on the Sun will be climbing up the sky each noon until June 21st next year when summer will start. To which I say Go Sun Go! The Sun will barely make it to 22 degrees above the southern horizon at local noon in Interlochen and be out for only 8 hours and 48 minutes. If it stayed that low all year we’d be in a deep freeze possibly colder than Antarctica.

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

Addendum

The Earth near the December solsitce

DSCOVR satellite’s Earth Polychromatic Camera image of the Earth at 18:09 UTC (1:09 p.m.) December 19, 2017. We’re way up at the top just under the clouds at the top. It was actually partly cloudy that day. The DSCOVR satellite was in a halo orbit about the Earth-Sun L1 point, 934,498 miles (1,503,929 km) toward the Sun from Earth.

The Sun at the solstice

The Sun is shown against the celestial sphere at the moment of the December solstice. Saturn will be in conjunction later in the day, heading to the right along the ecliptic, which is the path of the Sun. Venus will pass the Sun, heading to the left on January 9th. The grid lines are right ascension in hours (h) and declination in degrees. The solstice occurs when the Sun crosses the 18 hour line. Note the Teapot asterism that is part of Sagittarius. Created using Stellarium.

12/20/2016 – Ephemeris – The last full day of autumn

December 20, 2016 Comments off

Ephemeris for Tuesday, December 20th.  The Sun will rise at 8:16.  It’ll be up for 8 hours and 48 minutes, setting at 5:04.  The Moon, at last quarter today, will rise at 12:46 tomorrow morning.

Today is the last full day of autumn.  Tomorrow at 5:45 a.m.  winter will begin as the Sun passes the winter solstice and stops its southward movement in the sky.  Immediately it will slowly climb northward again.  It will lengthen the daytime hours and increase the power of the Sun as it gets higher in our sky.  The cooling of the northern hemisphere will continue until late January, on average, until the lengthening days and increased solar altitude will finally overcome it.  Prescientific cultures weren’t all that sure that Sun would come back, since they didn’t understand what was really happening.  So when the solstice finally arrived it was a time for great celebrations which survive to this day.

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

Addendum

Solstices

Comparing the sun’s path at the summer and winter solstices. This is a stereographic representation of the whole sky which distorts the sky and magnifies the size of the sun’s path near the horizon.

Take heart snow haters. Winter is the shortest season.  You’ll find out why in early January.

12/22/2015 – Ephemeris – Welcome to winter, or summer if you’re down under

December 22, 2015 Comments off

Ephemeris for Tuesday, December 22nd.  The Sun will rise at 8:17.  It’ll be up for 8 hours and 48 minutes, setting at 5:05.   The Moon, 3 days before full, will set at 5:59 tomorrow morning.

Today is the first full day of winter.  For folks south of the equator this is the first full day of summer.  The Earth reached a point in its orbit where its north pole is tipped its furthest away from the Sun, and is in shadow in the middle of it’s six month night.   We do see the Sun, though less than 9 hours of daylight, and to boot the Sun only rises 22 degrees above the horizon giving us the least amount of energy of any day of the year.  Why did the ancients celebrate this time of year?  That’s because the Sun had slowed and stopped its drift southward and was beginning to come back higher in the sky.  They still had to go through the worst of winter, but the Sun was coming back.  Spring and summer would eventually return!

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

Addendum

Solstices

Comparing the sun’s path at the summer and winter solstices. This is a stereographic representation of the whole sky which distorts the sky and magnifies the size of the sun’s path near the horizon.

The above chart shows the diurnal path of the Sun at the winter and summer solstices for Traverse City, MI near 45º north latitude.  Peak Sun altitude at noon at the winter solstice is 22º, while it’s 69º at the summer solstice.

 

 

12/21/2015 – Ephemeris – Except for 12 minutes today is the last day of autumn.

December 21, 2015 Comments off

Ephemeris for Monday, December 21st.  The Sun will rise at 8:16.  It’ll be up for 8 hours and 48 minutes, setting at 5:04.   The Moon, 3 days past first quarter, will set at 4:50 tomorrow morning.

Here we are at the mostly last day of autumn.  The last 12 minutes will be the start of winter.   The winter solstice will occur at 11:48 this evening, here in the Eastern Standard Time Zone.  Next year winter will start 18 hours earlier.  The reason is that next year is a leap year and the addition of an extra day will push all the solstices and equinoxes back by about 18 hours.  Why only 18 hours?  18 hours is three-quarters of a day, and by this time next year we will have used up a quarter of that adjustment already.  The Earth takes approximately 365 and a quarter days to orbit the Sun, so a day is added every 4th year, except century years not divisible by 400.  I’ll discuss more about the implications of the solstice tomorrow.

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

Addendum

The Earth near December solstice

Not quite the solstice, this is the Earth on December 16th, 2015 taken by the EPIC camera on the DISCOVR spacecraft at the Sun-Earth L1 point, some 1.5 million miles (1 million km) from the Earth.  Credit:  NOAA.

 

12/22/2014 – Ephemeris – Roman solstice festivals that seem like our holiday season

December 22, 2014 Comments off

Ephemeris for Monday, December 22nd.  The sun will rise at 8:16.  It’ll be up for 8 hours and 48 minutes, setting at 5:05.   The moon, 1 day past new, will set at 6:17 this evening.

The Romans, around the time of Christ knew that the Sun would turn northward after the winter solstice.  Their ancestors may not have been.  They had two festivals around this time of year.  Saturnalia, from the 17th to the 23rd. A time of gift giving, parties, kind of like now.  The feast of Sol Invictus or the Unconquerable Sun was set on December 25th the then date to have thought to be the winter solstice.  I’m not sure if the Roman calendars were off 4 days or that it was the date they detected northward movement in the Sun.  Anyway that’s the date the Christians decided to celebrate Christ’s birth.  The Gospel of Luke with its shepherds being out all night guarding the sheep suggests that the birth was actually in the spring.

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

Addendum

Saturnalia

Saturnalia depiction.

12/19/2014 – Ephemeris – Winter starts on Sunday

December 19, 2014 Comments off

Ephemeris for Friday, December 19th.  The sun will rise at 8:15.  It’ll be up for 8 hours and 49 minutes, setting at 5:04.   The moon, 2 days before new, will rise at 6:27 tomorrow morning.

It’s looking like November and December should trade places in the calendar this year.  And whatever the prognosis for a white Christmas this year winter will arrive on time at 6:03 p.m. Sunday the 21st.  At that moment the Sun will hover over the Tropic of Capricorn before slowly beginning its journey northward.  It is the winter of December solstice.  In the sky the Sun will be moving about its fastest eastward near the border between Ophiuchus and Sagittarius along the great circle in the sky called the ecliptic that will bring it northward.  The Sun’s motion will slowly bring longer daylight hours and a higher altitude that will counteract the cold generated in the last month or so, and will start to warm the northern hemisphere up again.

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

Addendum

 December solstice 2014

The Earth as seen from the direction of the Sun at 6:03 p.m. EST (23:03 UT) December 21, 2014. The sun would be overhead at 23.5 degrees south latitude in the South Pacific. Created using Celestia.