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01/03/2022 – Ephemeris – We’re the closest we get to the Sun of the whole year today

January 3, 2022 Comments off

This is Bob Moler with Ephemeris for Monday, January 3rd, 2022. The Sun will rise at 8:20. It’ll be up for 8 hours and 54 minutes, setting at 5:14. The Moon, 1 day past new, will set at 6:14 this evening.

Today we are as close to the Sun as we’ll get for the rest of the year. The Earth will reach the perihelion point in its orbit at 7:59 this evening, at only 91.4 million miles. Since this is only a million and a half miles closer than average, it doesn’t affect the amount of heat the Earth as a whole gets from the Sun. But, since the Earth moves faster at perihelion than at any other time of the year, it makes winter the shortest season. Winter at 89 days is nearly 4 days shorter than the longest season, summer. I know, it doesn’t seem like it, but we live in Northern Michigan, and seemingly long winters come with the territory. January’s only major meteor shower, the Quadrantids, reaches peak at about 4 pm today. It reaches and falls off-peak rapidly, so we won’t have an impressive Quadrantid meteor shower this year.

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

Earth's orbit

The Earth’s orbit, somewhat exaggerated, showing perihelion and the seasons. Credit: “Starts with a Bang” blog by Ethan Siegel.

Illustration of Kepler's 2nd Law

Kepler’s Second Law of Planetary Motion: the imaginary line joining a planet and the Sun sweeps equal areas of space during equal time intervals as the planet orbits. Credit: NASA, a screen capture from a video Solar Systems Dynamics-Orbits and Kepler’s Laws.

A note on the naming of the Quadrantid meteor shower. Meteor showers get their names from the constellation or nearby star where the meteor seem to come from at their peak. That point is called the radiant. The Quadrantids were named because they came from a constellation called the Mural Quadrant, back when the shower was discovered. The Mural Quadrant didn’t make the modern list of 88 constellations. The area where the Mural Quadrant resided is an area between northern Boötes, Draco and the handle of the Big Dipper.

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.

10/08/2021 – Ephemeris – How the Fisher paints the trees their autumn colors

October 8, 2021 Comments off

This is Bob Moler with Ephemeris for Friday, October 8th. Today the Sun will be up for 11 hours and 20 minutes, setting at 7:09, and it will rise tomorrow at 7:51. The Moon, 2 days past new, will set at 8:35 this evening.

The tree leaves are beginning to turn to reds and yellows as we advance into autumn. The native Anishinaabe peoples, whose homeland we share, have a story about how that came to be. Of how a magical weasel-like creature called the Fisher or, in their native language, Ojiig, brought summer to the Earth from Skyland. For his trouble, he was shot with an arrow in his only vulnerable spot, the tip of his tail. As he fell to Earth Gichi Manitou, the Great Spirit, caught him and placed him in the sky where we see the Great Bear and the Big Dipper. Every late autumn night we see his tail, the handle of the dipper, slowly swooping down to the horizon where his bloody tail paints the trees with their autumn colors.

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.

Addendum

Fisher brushing his tail along the horizon

An animation of the Fisher brushing his tail along the horizon on autumn nights. Created using Stellarium and GIMP.

The Anishinaabe constellation drawings are from Ojibwe Sky Star Map Constellation Guide  by Annette S. Lee, William Wilson, Jeffrey Tibbets and Carl Gawboy available locally and online.  They are part of the latest editions of Stellarium, a free planetarium program.  Links to it are on the right.  Other information and links are available within the Stellarium.

Here’s one of the links: http://www.nativeskywatchers.com/.  It also contains links to Lakota star maps and lore.

09/23/2021 – Ephemeris – The Earth’s axial tilt gives us our seasons

September 23, 2021 Comments off

This is Bob Moler with Ephemeris for Thursday, September 23rd. Today the Sun will be up for 12 hours and 6 minutes, setting at 7:37, and it will rise tomorrow at 7:32. The Moon, 3 days past full, will rise at 9:03 this evening.

The Earth has an axial tilt* of about 23 and a half degrees, which gives us our seasons. Because the Earth rotates on its axis, it has a slight equatorial bulge. Earth’s polar diameter is 7,900 miles (12,714 kilometers) while its equatorial diameter is 7,926 miles (12,756 kilometers), a difference of 26 miles (42 kilometers). The gravitational tug on that equatorial bulge by the Moon and Sun actually keeps the tilt stable, but does cause the Earth’s axis to precess like a top slowing down. It’s why Polaris will no longer be our North Pole star in centuries to come, just as it wasn’t in centuries past. It’s also why the constellations of the zodiac no longer align with the astrological signs of Ptolemy’s zodiac of the second century AD.

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.

* Astronomers call axial tilt “obliquity” or “obliquity of the ecliptic”.

Addendum

The force causing precession

The Moon and Sun’s gravitational force act on the Earth’s equatorial bulge, attempting to cause the Earth to straighten up and fly right. Because the Earth is spinning, it acts like a gyroscope and the torque to straighten it up causes it to be applied 90 degrees away in the direction of the rotation causing the procession. Image credit: Open Course: Astronomy.

Precesssion of a spinning top

Precession of a spinning top: the spin axis traces the surface of a cone. The axis, in the case of the Earth, traces a circle of radius 23.5 degrees on the sky. Credit NASA.

Precesion animation

The 25,700-year cycle of precession traced on the sky as seen from near the Earth. The current North Pole star is Polaris (top). In about 8,000 years it will be the bright star Deneb (left), and in about 12,000 years, Vega (left center). The Earth’s rotation is not depicted to scale – in this span of time, it would actually rotate over 9 million times. Credit image: Tfr000, caption: Wikipedia.

09/21/2021 – Ephemeris – Autumn starts tomorrow

September 21, 2021 Comments off

This is Bob Moler with Ephemeris for Tuesday, September 21st. Today the Sun will be up for 12 hours and 12 minutes, setting at 7:41, and it will rise tomorrow at 7:30. The Moon, 1 day past full, will rise at 8:23 this evening.

Enjoy the last full day of summer. Summer will last until 3:21 pm (19:21 UTC) tomorrow, when the center of the Sun will cross the celestial equator, an imaginary line above the Earth’s equator, heading southward. At that instant, autumn will begin. Shortly after, the Sun will be up less than half the day. The day and the point in the sky that the Sun crosses is called the autumnal equinox. The word equinox means equal night, implying that day and light are of equal length. Geometrically that’s true, but the Earth’s atmosphere and the definition of sunrise and sunset, prolong daylight by a few minutes. The amount of heat we are getting and will get from the Sun cannot sustain our current temperatures, and it will get a lot colder on average before it gets warmer again.

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.

Addendum

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. When the Sun is on the celestial equator, it rises due east and sets due west. Credit: Bob Moler.

Sun's path on the equinox for TC-Interlochen

The Sun’s path through the sky on an equinox day from the Traverse City/Interlochen area in Michigan. The Sun is plotted every 15 minutes. This is a stereographic projection which compresses the image near the zenith and enlarges the image towards the horizon. Created using my LookingUp program.

Earth 3 days before autumnal equinox

Earth 3 days before autumnal equinox, 1:17 pm EDT, September 19, 2021. The mitten shape of Michigan was in the clear that day and is visible above center of the image. The image taken by the Earth Polychromatic Imaging Camera (EPIC) on the DSCOVR satellite in halo orbit around the Earth-Sun L1 Lagrange point, about a million miles sunward of the Earth. At the time, DSCOVR was 892,682 miles (1,436,797 kilometers) from Earth.

06/18/2021 – Ephemeris – Summer* will start Sunday night

June 18, 2021 Comments off

This is Bob Moler with Ephemeris for Friday, June 18th. Today the Sun will be up for 15 hours and 34 minutes, setting at 9:31, and it will rise tomorrow at 5:56. The Moon, 1 day past first quarter, will set at 2:41 tomorrow morning.

Summer is just a couple of days away, though we have already been sweltering through a very hot first half of June. Summer will officially arrive for us on Earth’s Northern Hemisphere at 11: 32 pm, June 20th. If you are south of the equator, winter will arrive. If you are listening to this on the Internet, or reading this on my blog, it’s 3:32 UT, June 21st. And to be season agnostic, it’s the June solstice. From the 20th to the December solstice, the first day of winter for we northern hemispherians, (I think that’s a word) the daylight hours will get shorter as the Sun heads south. Solstice means Sun standstill as it stops its northerly motion and will, after Sunday, head back south again. The Northern Hemisphere will still be heating up for another month.

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

* Summer in the Northern Hemisphere only. Winter starts in the Southern Hemisphere.

Addendum

The Sun's path on the summer solstice

The Sun’s path through the sky on the summer solstice day from Traverse City, MI. The Sun is plotted every 15 minutes. The Sun’s motion is constant. The closeness of the Sun plots at higher altitudes is an artifact of portraying a hemispherical sky on a flat screen. It is a stereographic projection. Created using my LookingUp program.

Earth and local area near summer solstice

Earth and magnified local area near summer solstice. Image taken near local noon June 17, 2020. Credit NOAA DSCOVR satellite orbiting the Sun-Earth L1 point 994,970 miles (1,601,432 kilometers) sunward from the Earth.

06/15/2021 – Ephemeris – Today we had the earliest sunrise of the year

June 15, 2021 Comments off

This is Ephemeris for Tuesday, June 15th. Today the Sun will be up for 15 hours and 33 minutes, setting at 9:30, and it will rise tomorrow at 5:56. The Moon, 2 days before first quarter, will set at 1:29 tomorrow morning.

Today is the day of the year with the earliest sunrise, which in the Interlochen/Traverse City area is 6:56 am. We are 5 days before the summer solstice, the longest day in terms of sunshine hours. With the Sun nearing its maximum angle above the celestial equator, the projection of the Earth’s equator on the sky it cuts those longitude timelines quicker because they are closer together than at the equator. This is counters somewhat the Sun’s speed slowing down as the Earth is reaching the farthest point in its orbit. The latest sunset will occur about June 26th, a span of 11 days. In December the span between the earliest sunset and latest sunrise because of the Sun’s increased speed, by being nearly at its closest to us, is 24 days.

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

Addendum

Sun crossing time lines

How the Sun’s declination affects how rapidly it appears to cross time lines (meridians)

Analemma components animated

These graphs show how the earth’s orbit eccentricity and tilt of the Earth’s axis (obliquity) affect sundial time keeping vs. actual clocks. This also affects sunrise and sunset times. The figure 8 in the lower right is the analemma, sometimes seen on old Earth globes, a graphical representation of the equation of time (sundial corrections from apparent to mean solar time).

Earliest and Latest Sunrises and Sunsets

Table of Earliest and Latest Sunrises and Sunsets during the year for Interlochen/Traverse City area of Michigan. This table was created for 2017, 4 years ago. However, the instant of the summer solstice occurred just after midnight on June 21st, That instant slipped back into just before midnight in 2021. This is why we use the Gregorian calendar. The slide is corrected by having 3 out of four century years being normal years.

03/19/2021 – Ephemeris – Enjoy this last full day of winter!

March 19, 2021 Comments off

This is Ephemeris for Friday, March 19th. Today the Sun will be up for 12 hours and 7 minutes, setting at 7:54, and it will rise tomorrow at 7:45. The Moon, 2 days before first quarter, will set at 2:23 tomorrow morning.

Spring is almost here. It will arrive at 5:37 tomorrow morning, so this is the last full day of winter, such as it was. That point in time and the point in the sky where the Sun crosses 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, which they actually were last Tuesday. Since western civilization has spread south of the equator where the seasons are reversed, our Northern Hemisphere spring equinox is the Southern Hemisphere’s autumnal equinox, so to be understandable to both hemispheres we generally say March or September equinox instead.

Addendum

Sun's path on the equinox for TC-Interlochen

The Sun’s path through the sky on an equinox day from the Traverse City/Interlochen area in Michigan. The Sun is plotted every 15 minutes. This is a stereographic projection which compresses the sky near the zenith and enlarges the sky toward the horizon. Created using my LookingUp program.

02/02/2021 – Ephemeris – Happy Groundhog Day

February 2, 2021 Comments off

This is Bob Moler with Ephemeris for Ground Hog Day, Tuesday, February 2nd. Today the Sun will be up for 9 hours and 53 minutes, setting at 5:53, and it will rise tomorrow at 7:59. The Moon, 2 days before last quarter, will rise at 11:48 this evening.

I’m not sure if Punxsutawney Phil will see his shadow this morning or not, but February 2nd was a special day to the ancients. It is also Candlemas day for the Catholic Church. It is also celebrated as a cross-quarter day. The middle of the season of Winter, though the exact date of the middle of winter is the 4th. And if Phil sees his shadow, and we do get 6 more weeks of winter, that’s OK too. By the calendar it is actually 6 weeks and 5 days to the vernal or spring equinox, the official end of winter. But this is northern Michigan. Of the other cross-quarter days, only one stands out today. It’s May 1st, May Day. The way this year has been going, winter has had a hard time getting started. But when it gets going… Look out!

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

Addendum

Ground Hog Day

Poor Punxsutawney Phil, rousted out of his mid winter nap on a previous Groundhog Day. Phil looks kind of grumpy. I don’t blame him.  Credit: http://www.fuzzytoday.com.

 

12/22/2020 – Ephemeris – Winter is going to be colder before it starts to warm up in a little over a month

December 22, 2020 Comments off

This is Ephemeris for Tuesday, December 22nd. Today the Sun will be up for 8 hours and 48 minutes, setting at 5:05, and it will rise tomorrow at 8:18. The Moon, 1 day past first quarter, will set at 1:47 tomorrow morning.

Now that winter is here, it’s going to get snowier and colder even though the amount of heat the Northern Hemisphere gets from the Sun bottomed out yesterday. There are two consequences of the Earth’s axial tilt with regard to the Sun on the winter solstice. First, the Sun is only up 8 hours 48 minutes. Second at its highest at local noon the Sun is so low, only 22 degrees above the horizon around here that its heat is spread out over a greater area so is diluted to only 40% of the peak heat we get from the Sun at noon on the summer solstice. And on the summer solstice the Sun stays up almost six and three-quarters of an hour longer. Even though it doesn’t feel like it at our latitude winter is 4 days shorter than summer. You’ll find out why in less than two weeks.

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.

Earth's position at the solstices and equinoxes

Earth’s position at the solstices and equinoxes. This is an 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. Click on the image to enlarge. Credit: ESO (European Southern Observatory which explains the captions in German and English.