Archive
Ephemeris: 08/03/2026 – The Milky Way, a spiral galaxy with a bar
This is Ephemeris for Monday, August 3rd. Today the Sun will be up for 14 hours and 34 minutes, setting at 9:05, and it will rise tomorrow at 6:32. The Moon, 2 days before last quarter, will rise at 11:07 this evening.
The Milky Way is classed as a barred spiral galaxy. It has an apparent spiral structure in its disk illuminated by bright massive short lived stars that don’t stray far from the nebulae they were born from. Nebulae, mostly dark, form the backbone of the spiral structure. The Andromeda Galaxy is also a spiral, a little larger than our Milky Way Galaxy. Dwarf galaxies like the Magellanic clouds which are seen from the southern hemisphere of the earth that happen to be satellites of the Milky Way, and are irregular in shape. A third type of galaxy is the elliptical galaxy, many of which are extremely large and contain pretty much nothing but old stars, and no nebulosity to make new ones.
The astronomical event times given in this blog are for the Traverse City/Interlochen area of Michigan (Lat 44.7° N, Long 85.7° W; EDT, UT – 4 hours) unless stated otherwise. Times will be different for other locations.
Addendum
Ephemeris: 07/30/2026 – The types and distribution of galaxies
This is Ephemeris for Thursday, July 30th. Today the Sun will be up for 14 hours and 44 minutes, setting at 9:10, and it will rise tomorrow at 6:27. The Moon, 1 day past full, will rise at 9:52 this evening.
Until a little over 100 years ago the Milky Way was thought to be the whole universe. Then with photography the great Andromeda nebula turned out to be not a cloud of gas but a great group of stars outside. Since then we have found billions upon billions of these galaxies. Galaxy simply is a derivation from “Milky Way” in Latin. Galaxies are not sprinkled through the universe uniformly. They appear in great clusters and in small groups. The Milky Way and the Andromeda Galaxy belong to a relatively small group of galaxies called the Local Group, which contains 130 or more, mostly dwarf galaxies of which Andromeda and our Milky Way are the largest. The Great Andromeda Galaxy will come in view into the evening sky this autumn.
The astronomical event times given in this blog are for the Traverse City/Interlochen area of Michigan (Lat 44.7° N, Long 85.7° W; EDT, UT – 4 hours) unless stated otherwise. Times will be different for other locations.
Addendum
Ephemeris: 07/28/2026 – The size and shape of the Milky Way
7/
This is Ephemeris for Tuesday, July 28th. Today the Sun will be up for 14 hours and 48 minutes, setting at 9:13, and it will rise tomorrow at 6:25. The Moon, 1 day before full, will set at 6:11 tomorrow morning.
August and September are the two months in which the Milky Way dominates the evening sky. It also dominates the sky in the winter, six months from now but we’re looking out away from the center of the Milky Way. It is dimmer, an almost invisible as a band, but we have a great number of really bright stars, including those of Orion. The Milky Way is a galaxy, a large conglomeration of stars that are arranged in a disk, with the central bulge, whose diameter is about 87,400 light years. The thickness of the disk runs from 8,500 light years near the center to 1,000 light years farther out. The sun’s location is 25 to 26,000 light years from the center. From our location within the disk it appears to be a glowing band that surrounds the sky.
The astronomical event times given in this blog are for the Traverse City/Interlochen area of Michigan (Lat 44.7° N, Long 85.7° W; EDT, UT – 4 hours) unless stated otherwise. Times will be different for other locations.
Addendum
Ephemeris: 07/24/2026 – AI, a paradigm shift in computing
This is Ephemeris for Friday, 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, 3 days past first quarter, will set at 2:15 tomorrow morning.
Astronomy is my hobby. Back in my working days I was a computer systems analyst designing computer software systems for particular tasks, mainly for banks. However I was always interested in the idea of artificial intelligence. The computers I worked with were dumb. They did exactly what you told it to do, whether it was correct or not. So computer errors were really human errors. The current AI, based on neural networks, which are an approximation of what happens in the human brain, are different. Their errors are their own, because they are taught rather than programmed. And to my mind are more than the sum of their inputs. Even the people who design these systems admit they don’t really know what goes on inside. Scary.
The astronomical event times given in this blog are for the Traverse City/Interlochen area of Michigan (Lat 44.7° N, Long 85.7° W; EDT, UT – 4 hours) unless stated otherwise. Times will be different for other locations.
Ephemeris: 07/23/2026 – Our location in the Eastern Time zone
This is Ephemeris for Thursday, July 23rd. Today the Sun will be up for 14 hours and 59 minutes, setting at 9:18, and it will rise tomorrow at 6:20. The Moon, 2 days past first quarter, will set at 1:36 tomorrow morning.
Continuing my discussion about daylight savings time: In theory time zones are supposed to be centered on longitude meridians 15º apart, starting at 0° through Greenwich Observatory in England and proceed eastward and westward. our time meridian for Standard Time (75º west longitude) runs through Philadelphia, Pennsylvania, far to the east. The central standard time meridian runs down just east of Ironwood, Michigan. Most of us in the western lower peninsula are between 85 and 86° west longitude, meaning that we are already from 40 to 45 minutes behind our time meridian in Philadelphia and Eastern Daylight Time we are an hour and 40 to 45 minutes behind our daylight time meridian which is out in the Atlantic Ocean at 60° west longitude.
The astronomical event times given in this blog are for the Traverse City/Interlochen area of Michigan (Lat 44.7° N, Long 85.7° W; EDT, UT – 4 hours) unless stated otherwise. Times will be different for other locations.
Addendum
Ephemeris: 07/06/2026 – The Sun is farthest away from Earth today!
This is Bob Moler with Ephemeris for Monday, July 6th. Today the sun will be up for 15 hours and 26 minutes, setting at 9:30, and it will rise tomorrow at 6:05. The Moon, 1 day before last quarter, will rise at 12:42 tomorrow morning.
Today at 10:59 AM the Earth reaches aphelion from the Sun, the farthest it gets from it during the year. Earth will be 94 and a half million miles away from the Sun, a bit farther than our normal 93 million. In a planet’s orbit of the Sun, the Earth is no exception; it moves slowest when farthest from the Sun than when it’s closer, and fastest when at perihelion, its closest. It doesn’t make much difference in the amount of heat we get from the Sun being only 1½% farther than average. But it makes summer the longest season at 94 days, versus winter’s 89 days. OK, I know it doesn’t feel like it here in Northern Michigan, but count the days between each solstice and the next equinox.
The astronomical event times given in this blog are for the Traverse City/Interlochen area of Michigan (Lat 44.7° N, Long 85.7° W; EDT, UT – 4 hours) unless stated otherwise. Times will be different for other locations.
Addendum
Ephemeris: 06/29/2026 – Red stars large and small
This is Ephemeris for Monday, June 29th. Today the Sun will be up for 15 hours and 32 minutes, setting at 9:32, and it will rise tomorrow at 6:00. The Moon, at full today, will rise at 9:53 this evening.
There are two kinds of red stars very bright ones and very dim ones. The bright red ones are very few. One of them in the evening sky now is Antares in the heart of Scorpius the scorpion. Another one is in the winter sky and the most famous red giant of all, Betelgeuse in the shoulder of Orion the hunter. These are giant stars have exhausted the hydrogen in their cores to produce helium and are working on helium or even heavier elements fusing them to still heavier elements at even higher temperatures to keep them alive, but since they are working on the ash of the previous reaction, they won’t last very long, and the star dies, possibly cataclysmically. The higher internal heat bloats the star to be, huge, making its outer layers are actually cooler.
The astronomical event times given in this blog are for the Traverse City/Interlochen area of Michigan (Lat 44.7° N, Long 85.7° W; EDT, UT – 4 hours) unless stated otherwise. Times will be different for other locations.
Addendum
Ephemeris: 06/26/2026 – How do we know so much about those points of lights in the sky?
This is Ephemeris for Friday, 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, 3 days before full, will set at 3:37 tomorrow morning.
All but a handful of stars are mere points in even our largest telescopes. How do we know so much about them then? The reason is the science of spectroscopy, breaking down light into its constituent colors where color equals frequency or the energy of the light. Isaac Newton was the first to discover that by passing white light through a prism it turned into a rainbow of colors that the colors were actually combined within the white light. Passing sunlight through a vertical slit and smearing the light horizontally with the prism into its constituent colors, many dark vertical lines within that spectrum of colors appear. They turned out to be the fingerprints of the elements within the atmospheres of the stars, and that is just the beginning.
The astronomical event times given in this blog are for the Traverse City/Interlochen area of Michigan (Lat 44.7° N, Long 85.7° W; EDT, UT – 4 hours) unless stated otherwise. Times will be different for other locations.
Addendum
Ephemeris: 06/25/2026 – The color of stars
This is Ephemeris for Thursday, June 25th. Today the Sun will be up for 15 hours and 34 minutes, setting at 9:32, and it will rise tomorrow at 5:58. The Moon, halfway from first quarter to full, will set at 3:03 tomorrow morning.
Looking out at the night sky casually, the first impression is that the stars all appear to be white. Closer inspection shows that some appear with tinges of red or orange or maybe yellow while other stars have a bluish cast to them. The color of stars is due to their surface temperature which physicists call black body radiation. A rainbow is a spectrum of colors from red through orange yellow green blue and violet. These colors represent the different wavelengths of light. The peak wavelength determines the star’s surface temperature. The Sun’s in the green in the middle of our visual field. Cooler stars have their peak in the red, while hotter stars have their peak output to the blue end of the spectrum.
The astronomical event times given in this blog are for the Traverse City/Interlochen area of Michigan (Lat 44.7° N, Long 85.7° W; EDT, UT – 4 hours) unless stated otherwise. Times will be different for other locations.
Addendum
Ephemeris: 04/28/2026 – Stars spend most of their lives fueled by hydrogen
This is Ephemeris for Tuesday, April 28th. Today the Sun will be up for 14 hours and 7 minutes, setting at 8:44, and it will rise tomorrow at 6:35. The Moon, 3 days before full, will set at 5:24 tomorrow morning.
A star is a gaseous ball made mostly of hydrogen, which due to its mass crushes down in its core to create heat in the millions of degrees. Under those temperatures and pressures hydrogen nuclei, stripped of their electrons can collide to convert into helium and in doing so lose a tiny bit of mass that turns into energy which is used to sustain the star’s light and keep it stable. This hydrogen burning, so to speak, takes place during the longest period of a star’s life. And stars have a characteristic color based on their mass. Stars with little mass are cooler and appear a dim red. We call them red dwarfs. The nearest star to our solar system is a red dwarf called Proxima Centauri. It’s so dim that it’d be difficult to find with a pair of binoculars. And it’s only four light years away.
The astronomical event times given in this blog are for the Traverse City/Interlochen area of Michigan (Lat 44.7° N, Long 85.7° W; EDT, UT – 4 hours) unless stated otherwise. Times will be different for other locations.
Addendum
The HR diagram above shows the various types and brightness of stars. The relatively thin line of stars from upper left to lower right, called the main sequence, are stars that are running primarily on hydrogen as a fuel. At the bottom end of the main sequence small stars with a fraction of the sun’s mass. All these stars are near the sun. It doesn’t mean that we live in a bad neighborhood, but that the most numerous stars are red dwarfs, and we just can’t see them when they’re farther away. All the other stars are not using as hydrogen as their main fuel source. Stars the upper right are using heavier elements to produce energy from the fusion products of lighter elements, after having run out of hydrogen in their cores. The white dwarf stars in the lower part of the diagram no longer have active thermonuclear reactions in their cores and are cooling down and collapsing. A star with the mass of the sun, when it becomes a white dwarf, will shrink down to about the size of the earth.
Bob Moler's Ephemeris Blog 