Archive
Ephemeris: 07/24/2023 – The Moon appears to wobble a bit
This is Ephemeris for Monday, July 24th. Today the Sun will be up for 14 hours and 57 minutes, setting at 9:17, and it will rise tomorrow at 6:21. The Moon, 1 day before first quarter, will set at 12:24 tomorrow morning.
The Moon tonight is nearly half illuminated. In binoculars the dark oval spot visible on the Moon’s right edge is the Sea of Crises or Mare Crisium a small dark lava plain. The Moon’s rotation is quite uniform, however its orbit isn’t circular, so the Moon’s motion in its orbit slows as it moves farthest from the Earth, called apogee, and is sped up when closest, at perigee, So its face seems to rock a bit back and forth over the month. It’s an effect called libration. And one way to track that is to note how close the Mare Crisium (Sea of Crises) is to the edge of the Moon. It appears close to the right edge now. A week from now, that sea will appear to move away from the edge. Unfortunately, by then the Moon will be full, and night will soon fall on that little sea.
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
07/14/2023 – Ephemeris – Finding Polaris and why it’s important
This is Bob Moler with Ephemeris for Friday, July 14th. Today the Sun will be up for 15 hours and 16 minutes, setting at 9:26, and it will rise tomorrow at 6:11. The Moon, 3 days before new, will rise at 3:46 tomorrow morning.
The most important star in the night sky, especially if you are lost, is Polaris, also called the North Star or Pole Star. Face Polaris and North is in front of you, East is to the right, west to the left and south will be behind you. To find Polaris, first find the Big Dipper. In the evening. This time of year, it’s hanging by its handle in the northwest, the direction that the sun set at. The two stars at the front of the bowl point to Polaris, which is to the right of it, now. Throughout the night, as the Earth rotates. Polaris will hold its position as all the other stars go around it in a counterclockwise direction. Polaris is at the end of the handle of the Little Dipper. That handle start’s vertically but curves to the left and is made of faint stars.
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
07/06/2023 – Ephemeris – Today the Earth is farther from the Sun than anytime this year
This is Ephemeris for Thursday, July 6th. Today the Sun will be up for 15 hours and 26 minutes, setting at 9:30, and it will rise tomorrow at 6:04. The Moon, halfway from full to last quarter, will rise at 12:16 tomorrow morning.
Today, the Sun is at its farthest distance from the Earth. It’s called aphelion. The exact time actually occurred at 4:59 this morning at a distance of 94 and a half million miles away. Because of the gravitational pull of the Moon and planets on the Earth, especially Jupiter and Venus and gravitational pull of the planets, especially Jupiter on the Sun, the aphelion and perihelion, the closest date in January don’t occur on the same date or same distance every year. The date wanders by a day or two each year. The entire distance variation of the Earth from the Sun is plus or minus 1.5 million miles (2.4 million kilometers) over the year, makes summer the longest season by a few days because the Earth moves slower when farther from the Sun, than when it is nearer.
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.
Note: Apoapsis and Periapsis are generic terms for the farthest and nearest points in an orbit to the central body. For a body orbiting the Sun, it’s aphelion and perihelion. For a satellite of the Earth, it’s apogee and perigee.
06/26/2023 – Ephemeris – After the latest sunset, a look at the Moon
This is Ephemeris for Monday, June 26th. Today the Sun will be up for 15 hours and 33 minutes, setting at 9:32, and it will rise tomorrow at 5:59. The Moon, at first quarter today, will set at 2:02 tomorrow morning.
Tonight is the night of the latest sunset. From now to December 10th the Sun will be setting earlier than the night before. It won’t be noticeable at first, but the change will increase throughout the summer. The Moon actually arrived at first quarter phase early this morning, so by tonight it will appear slightly gibbous. The term gibbous actually means hump-backed, and the Moon will appear more so as it advances toward being fully illuminated a week from now. For me personally, I find that the best time to view the Moon with a telescope is within three or four days from its quarter phase, unless I’m looking at a specific feature. That’s when shadows are front and center on the moon. The Moon being gray on gray, shadows keep the Moon from appearing flat.
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
06/16/2023 – Ephemeris – Twilight is longer near the summer solstice
This is Ephemeris for Friday, June 16th. 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 new, will rise at 5:04 tomorrow morning.
Not only does the Sun set later this time of year, but twilight lasts longer too. As of tonight the end of astronomical twilight, when the last vestiges of twilight are gone is, for the Traverse City/Interlochen area, 12:01 am, That’s two and a half hours of evening twilight. I feel that for most purposes that the end of nautical twilight, when navigators on ships could no longer see the horizon for their sextant readings, is dark enough to view most stars, and brighter objects beyond the solar system, what we call deep sky objects. That happens at 10:56 pm, or about an hour and a half after sunset. Twilight of both kinds are a third shorter around the equinoxes. These times are dependent on our latitude, and the Sun’s declination which is equivalent to latitude.
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
Check out my September 27, 2018 post about the different twilight periods.
06/15/2023 – Ephemeris – Today we have the earliest sunrise of the year
This is Ephemeris for Thursday, 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, 3 days before new, will rise at 4:28 tomorrow morning.
Today is the day of the earliest sunrise, though the time will stay within the same minute for a few days. In six days the Sun will reach it’s farthest north in our sky. And be above the horizon for fifteen hours and thirty four minutes. That’s the summer solstice for those living in the north hemisphere. It’s also known as the longest day. The retired computer programmer in me likes to take things literally, so no, June 21st, the summer solstice is not the longest day. It’s 24 hours long, like any other day, however it has the longest daylight hours. Daylight hours being defined as the time interval from sunrise to sunset, which, in Interlochen and Traverse City, is 15 hours 34 minutes. Five or six days later, we’ll have the latest sunset.
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 the Earth had no axial tilt and had a circular orbit of the Sun, The earliest sunrise and latest sunset would occur on the summer solstice. But since that is not the case the Earth’s axial tilt and elliptical orbit cause the the earliest sunrise and latest sunset to differ from each other and the summer solstice.
04/24/2023 – Ephemeris – The reason for the Moon’s phases
This is Bob Moler with Ephemeris for Monday, April 24th. Today the Sun will be up for 13 hours and 55 minutes, setting at 8:38, and it will rise tomorrow at 6:42. The Moon, 3 days before first quarter, will set at 2:02 tomorrow morning.
The Moon’s changing appearance over the month may seem to be mysterious at first glance. Maybe because one may think that the objects in the sky are somehow different from the familiar objects we see around us on the Earth. In ancient times, especially the Greeks, thought that everything in the heavens was perfect and spotless. They explained the definite markings we see as the man-in-the-moon as a reflection of the Earth by a spotless Moon. The Moon’s phases are simply light and shadow on a ball in the sunlight. Sometime, when the Moon appears in the daytime, take a small ball, like a golf ball and hold it up to the Moon, while the ball is also in sunlight, and the small ball will exhibit the same phase as the Moon.
The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT –4 hours). They may be different for your location.
Addendum
This is the best diagram of the Moon’s phases and how the it appears from the Earth. Credit http://planetfacts.org/phases-of-the-moon/ which I recommend.
A demonstration of the Moon’s crescent phase with the styrofoam moon ball we use for Project Astro held up to a light off frame to the right. The line between the bright (day) and dark (night) side of the ball, moon or planet is called the terminator. The night side of the ball is illuminated a bit by the translucency of the ball, and the reflection off my hand. Note the roughness of the ball is visible only at the terminator, where the shadows are longest. I photographed this outside at night to minimize the ball’s nighttime illumination.
04/18/2023 – Ephemeris – Orion rotates 90 degrees from rising to setting
This is Bob Moler with Ephemeris for Tuesday, April 18th. Today the Sun will be up for 13 hours and 37 minutes, setting at 8:31, and it will rise tomorrow at 6:52. The Moon, 2 days before new, will rise at 6:43 tomorrow morning.
As the constellation of Orion the hunter, that dominated our winter skies, moves into the west in the evening, it will have rotated 90 degrees from its rising orientation. As we saw it rising last November, its three belt stars were nearly vertically aligned. Now, as Orion nears the western horizon, those belt stars have rotated to be almost horizontal. The same is true of Gemini’s two brightest stars, Castor and Pollux. They are the two stars above red Mars, which is now halfway through Gemini on its eastward travels. Orion, a minor Greek hero, is most famous for how he died. I know of three versions, all different. The one that fits Orion’s current setting is that he was killed by the sting of a giant scorpion. So he must flee the sky before Scorpius the scorpion rises, which is around midnight tonight.
This amount of rotation between rising and setting is only true for latitudes near 45 degrees north or south, such as Northern Michigan, and objects near the celestial equator. The rotation for other latitudes would be 2 x (90 – latitude) for equatorial celestial objects. The name given for the term (90 – latitude) is colatitude. 90 degrees is the latitude of the Earth’s poles.
The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT –4 hours). They may be different for your location.
Addendum
When Orion is rising, its belt stars are nearly vertically aligned. Castor and Pollux, too, appear nearly vertically aligned. This was for November 30, 2022, at 9 pm. Mars was near opposition then and quite close to the Earth, so it had shown quite brightly. Created using Stellarium and LibreOffice Draw.
Orion’s belt stars show that the constellation has rotated about 90 degrees from their rising orientation. This is for 10 pm, April 18, 2023. Note that Venus is the Evening Star now, and Mars is much dimmer, as the Earth has moved ahead and away from it. Created using Stellarium and LibreOffice Draw, for the added labels.
03/21/2023 – Ephemeris Extra – Spring has sprung without me
Being in the hospital and now in inpatient rehab one loses a sense of time. So the vernal equinox snuck by me unnoticed. My view of the outside world is another part of the hospital, a part of the HVAC system, and a piece of sky.
Yesterday, the Sun passed over the Earth’s equator, heading northward. The Sun is gradually setting at the South Pole and rising at the North Pole. Folks like me who live in the Northern Hemisphere are experiencing longer daylight than those south of the equator, who are beginning autumn. The daylight hours will increase daily until June 21st, the summer solstice. In the Interlochen/Traverse City area, that will be 15 hours and 34 minutes.
The cause of the Earth’s seasons is not our varying distance from the Sun in our eliptical orbit of the Sun of 93 million plus or minus a million and a half miles.By the way, the Earth is currently moving away from the Sun. It will be farthest from the Sun around July 4th or 5th.
Our perception of the advance of spring, besides the gradully warming temperatures and increasing daylight hours, will be the height of the Sun’s path in the sky, and the position of the Sun’s rise and set points on the horizon. All these annual changes are angles having to do with one’s latitude (an angle), Earth’s position in orbit (an angle), and the tilt of the Earth’s axis to it’s orbit (more angles).
Bob
02/07/2023 – Ephemeris – A new view on the creation of our Moon
Feb 7. This is Bob Moler with Ephemeris for Tuesday, February 7th. Today the Sun will be up for 10 hours and 5 minutes, setting at 5:59, and it will rise tomorrow at 7:53. The Moon, 2 days past full, will rise at 7:58 this evening.
Is this how the Moon came to be? After the Apollo missions, NASA decided to look at the crust of the Moon which apparently is much like the Earth’s and came up to the conclusion that a Mars sized body they called Theia, after the mother of the twins Apollo and Artemis, crashed into the Earth at about a 45-degree angle, and caused a ring of debris around the Earth that would be maintained for a long time. In a newer simulation, the collision could actually create two blobs of material, a large one that became our Moon, in orbit, with about one percent of the Earth’s mass, and a smaller mass that fell back onto the Earth.
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
A new simulation on how the Moon formed. Credit: PBS.
Bob Moler's Ephemeris Blog 