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06/02/2022 – Ephemeris – What’s an ephemeris?

June 2, 2022 Comments off

This is Ephemeris for Thursday, June 2nd. Today the Sun will be up for 15 hours and 22 minutes, setting at 9:22, and it will rise tomorrow at 5:59. The Moon, 3 days past new, will set at 12:34 tomorrow morning.

Yesterday, I was too busy on this program to mention that that program was the 47th anniversary of the Ephemeris program and was embarking on its 48th orbit of the Sun. At this juncture, you might be wondering: What’s an ephemeris? According to Wikipedia: Quote “In astronomy and celestial navigation, an ephemeris (plural: ephemerides; from Latin ephemeris, meaning ‘diary’, from the Greek, … meaning ‘diary, or journal’) gives the positions of… astronomical objects… at a given time or times. Historically, positions were given as printed tables of values, given at regular intervals of date and time.” enquote. My tables are now databases which I generate for the year during the prior December from published algorithms. I will show all on my blog today: (You are already here). I used to have to interpolate values from printed ephemerides for the first 5 or so years of the program.

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

An Ephemeris Example – Comet 73P-B/Schwassmann-Wachmann 3 nuclear fragment B

A sample of an ephemeris

Here’s an ephemeris for Comet Schwassmann-Wachmann 3 nuclear fragment B from the Jet Propulsion Laboratory’s (JPL) Horizons system. The listing has been truncated for width. Click on it to enlarge it.

R.A. is right ascension – East-west position in the sky, like longitude on the Earth, only it’s in hours, minutes and seconds.  One hour = 15 degrees.

DEC is declination – North-south position, in the sky, exactly like latitude on the Earth in degrees, minutes and seconds.

(a-apparent) means that the above coordinates are based on where the vernal equinox point in the sky is at that date and time, and for the observer’s location. Since I didn’t specify one, it’s the center of the Earth.

T-mag – Predicted total magnitude of the comet.  Magnitudes are like golf scores.  The higher magnitude, the dimmer the object.  It’s really, really dim.

N-mag – Predicted magnitude of the nucleus. No estimate is made here.

r – Distance from the Sun in terms of Astronomical Units (AU).  1 AU is Earth’s mean distance from the Sun.

rdot – The change in r.  It’s in kilometers per second.  If negative, it’s moving toward the Sun.

For more information on how I produce ephemerides for this program, go here: https://bobmoler.wordpress.com/2019/01/22/

04/15/2022 – Ephemeris – How the date of Easter is determined

April 15, 2022 Comments off

This is Ephemeris for Good Friday, April 15th. Today the Sun will be up for 13 hours and 29 minutes, setting at 8:27, and it will rise tomorrow at 6:56. The Moon, 1 day before full, will set at 7:04 tomorrow morning.

Easter will be celebrated by Western 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. The Jewish calendar being a lunar calendar, the 15th is generally the night of the full moon. And since the Last Supper was a Seder, according to at least one Gospel, the Christian church wanted to link Easter with Passover as closely as possible using the Roman solar based (Julian) calendar. The months didn’t follow the cycle of the Moon anymore and where the year was 365.25 days long. Passover starts at sunset tonight. The western churches adopted the Gregorian calendar to keep in sync with the seasons. The Orthodox churches didn’t, so their Easter is a week later this year. They kept the old Julian Calendar and other considerations to calculate the date of Easter.

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

If you’re wondering about what all this has to do with astronomy? The answer is: Everything! Astronomy in ancient times wasn’t about the nature of planets, and stars, but about the cycles about the Sun and Moon. These cycles announced the seasons, and festival times. This is how the date of Passover is set. The Jews, at least in the Bible, only referenced the constellations of Orion and the Great Bear plus the star cluster Pleiades, that scholars have pinned down. There are two more possible references to constellations that don’t translate. These are all in the Book of Job. The only planet mentioned is Saturn, because it was thought to be closest to the firmament, the starry sphere.

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03/15/2022 – Ephemeris – The Ides of March and our calendar

March 15, 2022 Comments off

This is Ephemeris for Ides of March, Tuesday, March 15th. Today the Sun will be up for 11 hours and 53 minutes, setting at 7:49, and it will rise tomorrow at 7:53. The Moon, 3 days before full, will set at 7:36 tomorrow morning.

The first day of spring is the vernal equinox, which occurs in our time zone on March 20th. The Ides of March, the 15th, is pretty close to the vernal equinox and was the start of the year for a time with the Romans. It was the date in 44 BC that Julius Caesar was assassinated. March, named after the god Mars, was also for a long time the first month of the year, even to the point of starting the year on the Ides of March. They, for a time, had 10 months in their year, and consigned the winter months to sixty nondescript days. Later, they added January and February in front of March, which is why our 9th through 12th months are named September the 7th to December the 10th month.

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.

03/14/2022 – Ephemeris – It’s Pi Day!

March 14, 2022 Comments off

This is Ephemeris for Pi Day, Monday, March 14th. Today the Sun will be up for 11 hours and 50 minutes, setting at 7:47, and it will rise tomorrow at 7:55. The Moon, 4 days before full, will set at 7:10 tomorrow morning.

Mathematicians and scientists, both professional and amateur, celebrate Pi day to bake and eat pies. Actually, the Pi we’re talking about is the Greek letter π that signifies the ratio of the circumference of a circle to its diameter. March 14th can be written 3.14, π to two decimal places. Of course, if you wait until 4 pm to have your pie, you can have π to 4 decimal places, since 4 pm is the 16th hour of the day in military time. This gives 3.1416. The digits go on forever, never repeating a pattern. Some mathematicians prefer Tau Day, June 28th or 2 times π which is the more useful mathematical ratio of the circumference of a circle to its radius, which is 6.28 or 6.2832. However you slice it, π is a very useful number.

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

Have a slice of Pi Day pie

Here’s a link to NASA’s Pi Day Challenge: https://www.jpl.nasa.gov/edu/nasapidaychallenge/. The link also has a link for educators for STEM related challenges.

Since recording this program, I learned about another Pi day some celebrate. A well-known approximation of pi is the fraction 22/7ths. Europeans and others write dates in day/month order, so July 22nd is also a Pi Day: 22/7.

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.

02/27/2020 – Ephemeris – Saturday is the intercalary day

February 27, 2020 Comments off

Ephemeris for Thursday, February 27th. Today the Sun will be up for 11 hours and 2 minutes, setting at 6:27, and it will rise tomorrow at 7:22. The Moon, half way from new to first quarter, will set at 10:28 this evening.

Saturday we’re going to have one of those special days that only occur once every 4 years making this a leap year. It’s the intercalary day that compensates for the fact that the earth takes 365 and nearly a quarter day to orbit the Sun. That orbit is a year, and those quarter days are accumulated and added as the last day of February on years divisible by 4. The Gregorian reform makes a slight adjustment on most century years, making century years not divisible by 400 ordinary years to keep the calendar in sync with the seasons. The Romans, from who we’ve gotten our calendar considered the month of February as unlucky, and so they shortened it. Enjoy your extra day on Saturday.

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

 

01/07/2020 – Ephemeris – What the heck is an ephemeris? Plus my Betelgeuse update

January 7, 2020 Comments off

Ephemeris for Tuesday, January 7th. Today the Sun will be up for 8 hours and 58 minutes, setting at 5:18, and it will rise tomorrow at 8:19. The Moon, 3 days before full, will set at 6:09 tomorrow morning.

What the heck is an ephemeris? According to Wikipedia: “In astronomy and celestial navigation, an ephemeris (plural: ephemerides; from Latin ephemeris, meaning ‘diary’, from the Greek,… meaning ‘diary, <or> journal’) gives the positions of… astronomical objects… at a given time or times. Historically, positions were given as printed tables of values, given at regular intervals of date and time.” My tables are now databases which I generate for the year during the prior December from published algorithms. I will show all on my blog today: It’s at bobmoler<dot>wordpress<dot>com. (You are already here) I used to have to interpolate values from printed ephemerides for the first 5 or so years.

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

Addenda

An Ephemeris Example

Ephemeris for 2I/Borisov

Here’s an ephemeris for the Interstellar comet for 2I/Borisov AKA C/2019 Q4 (Borisov) from the Jet Propulsion Laboratory’s (JPL) Horizons system.

R.A. is right ascension – East-west position in the sky, like longitude on the Earth, only it’s in hours, minutes and seconds.  One hour = 15 degrees.

DEC is declination – North-south position, in the sky, exactly like latitude on the Earth in degrees, minutes and seconds.

J2000.0 means that the above coordinates are based on where the vernal equinox point in the sky was on January 1, 12:00 Terrestrial Time, 2000.  Or January 1, 2000, 11:58:55.816 UTC as reported in Wikipedia.

APmag – Apparent visual magnitude.  Magnitudes are like golf scores.  The higher magnitude the dimmer the object.  It’s really, really dim.

delta – Distance from the Earth in terms of Astronomical Units (AU).  1 AU is Earth’s mean distance from the Sun.

deldot – The change in delta.  It’s in kilometers per second.  If positive, it’s going away.

For more information on how I produce ephemerides for this program go here: https://bobmoler.wordpress.com/2019/01/22/

The dimming of Betelgeuse

I finally got a clear evening.  However snow and freezing rain the rest of the week.

Orion at 7:07 p.m. January 6, 2020

Betelgeuse in Orion at 7:07 p.m. January 6, 2020. Taken with my Samsung Galaxy S10+ in the moonlight. Compare the brightness of Betelgeuse with Rigel, Bellatrix and the belt stars.

Orion's brightest stars

Orion’s brightest stars with their names for 9 p.m. January 7, 2019. Click on the image to make Orion a giant hunter. Created using Stellarium.

See last Thursday’s post on the dimming of Betelgeuse: https://bobmoler.wordpress.com/2020/01/02/

01/06/2020 – Ephemeris – The Earth was closest to the Sun in its orbit yesterday

January 6, 2020 Comments off

Ephemeris for Monday, January 6th. Today the Sun will be up for 8 hours and 57 minutes, setting at 5:17, and it will rise tomorrow at 8:19. The Moon, half way from first quarter to full, will set at 5:02 tomorrow morning.

Yesterday’s perihelion, or closest point of the Earth to the Sun of roughly 91.4 million miles (147 million km) is only 1.7% closer to the Sun than average. It doesn’t do much to make our winters warmer, but it does make winter the shortest season. That’s because the Earth travels faster when near the Sun than when it’s farther away. Winter lasts only 89 ½ days. The Earth’s aphelion, when it’s farthest from the Sun will be on the 4th of July, in summer, making that the longest season at 93 ½ days. Of course being this far north it feels like winter is longer than summer, but astronomically it’s the other way around. Being a leap year, with February having 29 days, spring will arrive a calendar day early on the 19th of March.

The times given are for the Traverse City/Interlochen area of Michigan. 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.

Seasons for 2020

The Seasons for 2020 from data in Astronomical Tables of the Sun, Moon, and Planets Third Edition by Jean Meeus. Date and times are in TD, Dynamical Time. Subtract about 1 minutes to convert to Universal Time (UT).  Also subtract 5 hours for Eastern Standard Time and 4 hours for Eastern Daylight Time.

For and explanation of the Cross-Quarter Days column, check out my Ground Hog Day post last year:  https://bobmoler.wordpress.com/2019/02/02/02-02-2019-ephemeris-extra-groundhog-day-and-other-seasonal-days/

 

04/19/2019 – Ephemeris – Why Sunday is Easter

April 19, 2019 Comments off

Ephemeris for Good Friday, Friday, April 19th. Today the Sun will be up for 13 hours and 40 minutes, setting at 8:32, and it will rise tomorrow at 6:50. The Moon, at full today, will rise at 8:56 this evening.

Easter will be celebrated by western 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 (Julian*) calendar where the year was 365.25 days long. Passover starts at sunset tonight. The western churches eventually adopted the Gregorian calendar to keep in sync with the seasons. The Eastern churches kept the old Julian Calendar and other considerations to calculate the date of Easter, which arrives a week later.

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

* The Julian calendar is named after Julius Caesar who proposed it in 46 BC.  It took effect on January 1, 45 BC.  By the Julian calendar today is April 6.

03/18/2019 – Ephemeris – Spring, the full moon and Easter

March 18, 2019 Comments off

Ephemeris for Monday, March 18th. Today the Sun will be up for 12 hours and 2 minutes, setting at 7:52, and it will rise tomorrow at 7:48. The Moon, 2 days before full, will set at 7:21 tomorrow morning.

Spring is two days away. In checking my astronomical calendars I noticed an odd thing related to the date of Easter for western churches. If I said that the date of Easter was the first Sunday after the first full Moon after the vernal equinox. I’d be wrong. Even if I replaced vernal equinox with first day of spring, I would still be wrong by ecclesiastical standards. The ecclesiastical vernal equinox is March 21st, no matter what. Plus the full moon date is a tabulated value and not necessarily the astronomical full moon date. This year the astronomical first full moon of spring falls less than 4 hours after the astronomical vernal equinox on March 20th. Therefore Easter will be late this year on April 21st, 4 days earlier than its latest possible date.

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