Archive
Ephemeris: 03/15/2024 – The Ides of March
This is Ephemeris for Ides of March, Friday, March 15th. Today the Sun will be up for 11 hours and 55 minutes, setting at 7:49, and it will rise tomorrow at 7:52. The Moon, 2 days before first quarter, will set at 3:01 tomorrow morning.
Our calendar is derived from the Roman calendar. The Ides is the only named day ion the Roman calendar that we’re familiar with today, the Ides of March. On this day in 44 BCE Roman Emperor Julius Caesar was assassinated. The Ides of a month is the 13th of the month except for March, May, July, and October when it’s the 15th. The Roman calendar has two other named days. The 1st of the month is called Kalend, from which we get our word calendar. The other day is Nones which is the 5th day of the month except for March, May, July, and October when it’s on the 7th. The other days are countdown days to those dates so tomorrow will be the 17th day before the Kalend of April. The countdown is to 1 not 0, if you’re counting.
My source: https://www.slideserve.com/jonah/roman-calendar
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
This being a leap year, I will spend more time on these programs talking about the calendar. As you may know, we no longer use the Julian calendar for our normal calendar keeping functions. We use the Gregorian Calendar which is a modification of the Julian Calendar that was first made in the year 1582 CE. As we get closer to Easter I will delve into the Gregorian Calendar because it has everything to do with the date of Easter.
Ephemeris: 02/27/2024 – Thursday is the Intercalary Day
This is Bob Moler with Ephemeris for Tuesday, 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, 3 days past full, will rise at 9:47 this evening.
Thursday 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 that fact that the Earth takes 365 and a bit short of 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 in years divisible by 4. The Gregorian reform makes a slight adjustment to 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 most years to 28 days. Enjoy your extra day Thursday.
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
No calendar is perfect. The average year of the Julian Calendar is 11 minutes and 14 seconds longer than the actual seasonal year which it is trying to model. By the time of the papacy of Pope Gregory XIII from 1572 to 1585 CE the error in the Julian calendar versus the actual seasons had grown to 10 days since the Julian Calendar was established 16 centuries before. The reason the Church was concerned was that Easter was slowly advancing toward summer, and Easter is a more important feast than Christmas, but is related to the Jewish Feast of Passover. I’ll discuss the formula for determining Easter as we get closer to it. However, the Gregorian calendar reform came in two parts: Ten days were dropped from the calendar between October 4th and 15th in the year 1582 and after that the every four year leap day rule, that is years evenly divided by 4, was modified so that on century years, that is years ending in 00, but not divisible by 400, became ordinary years, that is no leap days, this will keep the calendar in sync with the seasons for several millennia. This calendar reform occurring after the Reformation meant that only the Catholic countries adopted it. It took almost until the present day for everyone to adopt it. For ecclesiastical purposes the Orthodox Churches still used the Julian Calendar.
Ephemeris: 02/26/2024 – The angle of the rising and setting planets from the Sun vary with the seasons
This is Bob Moler with Ephemeris for Monday, February 26th. Today the Sun will be up for 10 hours and 59 minutes, setting at 6:25, and it will rise tomorrow at 7:24. The Moon, 2 days past full, will rise at 8:44 this evening.
In late winter and early spring dark skies return within a few days after the full Moon. Indeed, this is the first day after the full moon, which was on Saturday morning, that we have dark skies. Well for 40 minutes before the Moon rises. This is because the ecliptic which is the Sun’s path in the sky is as close to vertical as it can get for us. It shows planets near the Sun and the area of the full moon as steeply inclined to the horizon as possible. Twelve years ago this month when my wife and I were on a Hawaiian cruise, I was aboard ship looking at the sky after sunset and was amazed to see Jupiter and Venus* vertically aligned in the west. It was because we were located around the Tropic of Cancer and near the equinox, so the ecliptic was actually vertical after sunset. It was quite a jolt to see that. So this time of year we can see planets close to the sun at sunset and the moon to go away after full rapidly.
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.
* On the broadcast I said Jupiter and Saturn, relying on my memory. As can be seen below, it was Jupiter and Venus.
Addendum
Ephemeris: 01/26/2024 – In astronomy “dark” means we can’t see it
This is Ephemeris for Friday, January 26th. Today the Sun will be up for 9 hours and 33 minutes, setting at 5:42, and it will rise tomorrow at 8:07. The Moon, 1 day past full, will rise at 6:37 this evening.
What does the word “dark” mean? In astronomy the word dark means something we cannot see. In ages before 1959 we could not see the backside of the moon, so people got to calling it the dark side of the Moon. All changed in 1959 when a Soviet spacecraft went around behind the moon it took photographs of it. The two contenders for dark things in astronomy are now dark matter and dark energy. Dark matter is something that has a gravitational effect on the galaxies that it surrounds, but we can’t see it. Also, the expansion of the universe appears to be accelerating, where we would expect it to be decelerating because of gravitational forces of all the galaxies in it. We call that cause dark energy. And we don’t know what either is.
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
Two possible causes of Dark Matter are in the running, WIMPs, and of course MACHOs. WIMPs are Weakly Interacting Massive Particles, while MACHOs are the bit more tortured acronym Massive Astrophysical Compact Halo Objects. Whatever they are they don’t interact much with themselves or ordinary matter, neither emitting light or any other radiation, or block it. However, they have mass and warp spacetime, distorting the shape of galaxies seen behind them. They also make galaxies seem to be more massive than their starlight would make them appear, and other effects.
Ephemeris: 01/25/2024 – Where is the full moon in winter?
This is Ephemeris for Thursday, January 25th. Today the Sun will be up for 9 hours and 31 minutes, setting at 5:41, and it will rise tomorrow at 8:08. The Moon, at full today, will rise at 5:30 this evening.
The exact time that the Moon will be full, at least to the nearest minute is 12:54 this afternoon. Have you ever noticed the placement of the full moon in the sky between winter and summer? The full moon near the winter solstice moves very high at midnight, while the full moon near the summer solstice is seen quite low in the south. For the Moon to be full, it must be nearly opposite the Sun in the sky, so we see it fully illuminated as the Sun does. The Moon’s orbit is close to the Sun’s apparent path in the sky, the ecliptic, which is the projection of the Earth’s orbit of the Sun. So the Moon now is near, and actually a bit north of, where the Sun will be 6 months from now in mid to late July.
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
Ephemeris: 12/21/2023 – Winter comes late this evening
This is Bob Moler with Ephemeris for Thursday, December 21st. Today the Sun will be up for 8 hours and 48 minutes, setting at 5:04, and it will rise tomorrow at 8:17. The Moon, 2 days past first quarter, will set at 3:37 tomorrow morning.
Today is mostly the last day of Fall, since the moment of solstice will arrive at 10:28 pm (03:28 on the 22nd UTC). 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 its 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 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
Ephemeris: 12/08/2023 – Tomorrow has the earliest sunset of the year
This is Ephemeris for Friday, December 8th. Today the Sun will be up for 8 hours and 55 minutes, setting at 5:02, and it will rise tomorrow at 8:08. The Moon, 3 days past last quarter, will rise at 4:28 tomorrow morning.
Tomorrow is the date of the earliest sunset, in the middle of a 12-day stretch where the Sun sets within the same minute. We are still 13 days from the winter solstice, the day of the shortest daylight hours, on the 21st. The reason is twofold. The Sun is near its farthest position south of the equator, where the longitude lines are closer together, so it takes less time to cross them. 15 degrees in longitude equals one hour in Earth’s rotation. Add to that we are less than a month from Earth’s perihelion in its orbit of the Sun, that is at its closest, and is moving faster than average. The combined effects delay sunrise and sunset, from what they’d be if the Sun was on the equator and the Earth’s orbit was circular. We will have our latest sunrise on January 2nd.
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
In December the Earth is approaching perihelion, its closest to the Sun, so it moves faster than average. This makes the Sun to appear to move faster eastward against the stars in our sky, and tends to make our sunrises, apparent local noons and sunsets later than they would otherwise be. Sunset bottoms out early and extends the date of the latest sunrise
For the June or summer solstice around here, the Earth is near aphelion, it’s farthest from the Sun where the Earth is at its slowest in its orbit. By reflection, the Sun appears to move its slowest against the stars in our sky. This effect works against the high latitude effect, making the effect smaller. Looking at the table above, the days between the earliest and latest times is shorter for the summer solstice than for the winter solstice.
Ephemeris: 11/27/2023 – Seeing in low light levels
This is Bob Moler with Ephemeris for Monday, November 27th. Today the Sun will be up for 9 hours and 10 minutes, setting at 5:05, and it will rise tomorrow at 7:56. The Moon, at full today, will rise at 5:01 this evening.
Today’s full moon is called the Beaver full moon actually the moon was exactly full at 4:16 this morning, so last night it was actually closer to full moon than it will be tonight. The bright full moon fills the sky with light so most of the fainter stars disappear. The sky looks gray when the moon is full, but it is just as blue as the daytime sky. It’s just that our eyes cannot discern color at low light levels. We sacrifice our color vision for night vision. Other animals can see in the dark much better than we can, though some of them do not have quite the color vision we have so viewing the skies and viewing the world around us is a compromise. We were evolved from creatures that were most active in the daytime and hid at night. My cats can see much better in the dark than I can. However, the other animals do not have the abilities we have to create tools and instruments to allow us to see better in the dark than they can.
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
Ephemeris: 09/28/2023 – Tomorrow night’s full moon is the Harvest Moon
This is Ephemeris for Thursday, September 28th. Today the Sun will be up for 11 hours and 52 minutes, setting at 7:29, and it will rise tomorrow at 7:38. The Moon, 1 day before full, will set at 7:43 tomorrow morning.
Tomorrow night’s full moon is the Harvest Moon. It is the most famous of the named full moons, and was very useful in the days before electric lights. The reason is that the Moon, around the time it is full, doesn’t advance its rising time very much from night to night, effectively adding its light to twilight to allow more time to gather in crops. This is because the Moon is moving north as well as eastward. The farther north it is, the longer it stays up and retards the advance in rise times. On average, the Moon rises 50 minutes later each night. This week, the interval is down near 22 minutes advance in moonrise times per day, extending twilight and the amount of time each day to harvest the crops for a few more days.
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
My interest in the Harvest Moon is not in harvesting the crops. I just have a little garden, so it doesn’t take that long to pick tomatoes or whatever. But as an amateur astronomer I’m more interested in deep sky objects than I am in planets. Deep sky objects or DSOs are objects beyond the solar system and are usually very dim, which requires dark skies to view them. Near the Harvest Moon and even in August near the full moon it takes nearly a week for that @#$%^&* Moon to get the heck out of the evening sky, so I don’t have to stay up till after midnight to see anything. That’s I why have this interest in the Harvest Moon. Know your enemy!
Ephemeris: 07/25/2023 – Is the universe twice as old as we think?
This is Ephemeris for Tuesday, July 25th. Today the Sun will be up for 14 hours and 55 minutes, setting at 9:16, and it will rise tomorrow at 6:22. The Moon, at first quarter today, will set at 12:44 tomorrow morning.
Is the universe twice as old as we thought? That’s a conclusion of a study printed in the monthly notices of the Royal Astronomical Society by Rajendra Gupta from the University of Ottawa, in which he postulates that the structure and chemical composition of very early galaxies found by the James Webb Space Telescope turn out to be more developed than one would expect for objects so soon after The Big Bang. The problem with hypothesizing an older universe is to explain what we see currently that have shown that the universe is 13.8 billion years old. One of the things he hypothesized was something called tired light, where light loses energy and is red-shifted not just because of the expansion of the universe but over time and distance. Stay tuned.
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
Timeline of the universe. A representation of the evolution of the universe over 13.77 billion years. The far left depicts the earliest moment we can now probe, when a period of “inflation” produced a burst of exponential growth in the universe. (Size is depicted by the vertical extent of the grid in this graphic.) For the next several billion years, the expansion of the universe gradually slowed down as the matter in the universe pulled on itself via gravity. More recently, the expansion has begun to speed up again as the repulsive effects of dark energy have come to dominate the expansion of the universe. The afterglow light seen by WMAP was emitted about 375,000 years after inflation and has traversed the universe largely unimpeded since then. The conditions of earlier times are imprinted on this light; it also forms a backlight for later developments of the universe. Public Domain.
Diagram is from Wikipedia. Above is the expansion of the universe as commonly understood. Not mentioned in the program script above, is the requirement, according to Gupta’s hypothesis, that the basic constants of the universe change over time. As Carl Sagan explained, “Extraordinary claims require extraordinary evidence.” So more evidence is needed. His hypothesis won’t be the only explanation put forth, so there will be more to test. That’s job security for astrophysicists and cosmologists.
Bob Moler's Ephemeris Blog 