Archive
Ephemeris: 07/31/2025 – The Perseids are coming
This is Bob Moler with Ephemeris for Thursday, July 31st. Today the Sun will be up for 14 hours and 41 minutes, setting at 9:09, and it will rise tomorrow at 6:29. The Moon, 1 day before first quarter, will set at 11:59 this evening.
Over the past couple of weeks folks who are outdoors after the Moon sets in the morning might have been seeing some shooting stars or meteors appearing to zip through the sky. The ones I’m talking about seem to come from the northeast. These are the precursors of the Perseid meteor shower which will reach its peak on the mornings of August 12 and 13 this year with the interference of a bright Moon. Over the millennia the meteoroid stream that feeds the meteors to our skies has spread out to last over a month from the latter half of July to three-quarters of August. I try to use the proper terminology for all this. A meteoroid is the tiny body in space. In the Perseid’s case the size of a grain of sand to a pea. Meteor is the streak we see in the sky as it burns up. A meteorite is the body that makes it to the ground. To my knowledge no Perseid has made it that far.
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: 07/30/2025 – Taking our weekly look at the Moon and the naked-eye planets
This is Ephemeris for Wednesday, July 30th. Today the Sun will be up for 14 hours and 43 minutes, setting at 9:10, and it will rise tomorrow at 6:28. The Moon, 2 days before first quarter, will set at 11:40 this evening.
Let’s take our weekly look at the whereabouts of the naked-eye planets. The Red Planet Mars, will be seen low in the western sky at 10:15 PM. Mars is moving toward Spica, higher in the west-southwest, which will be above the Moon tonight. Mars will pass Spica on September 12th. By then they will be too low in the sky to be seen in twilight. Saturn now rises at 11:15 PM in the east. When I had my first telescope, eagerly waiting for Saturn to rise, I had to wait more than a half hour to get a sharp image of it. By 5:30 AM Saturn will be high in the south, when our winter pal Orion will be rising. Venus will rise at 3:29 AM in the east-northeast and will be higher in the east by 5:30. Jupiter will be below and left of Venus.
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: 07/29/2025 – Altair, the nearest Summer Triangle star
This is Ephemeris for Tuesday, July 29th. Today the Sun will be up for 14 hours and 45 minutes, setting at 9:11, and it will rise tomorrow at 6:27. The Moon, 3 days before first quarter, will set at 11:23 this evening.
The southernmost star of the Summer Triangle is Altair, high in the east-southeast. The other two stars of the triangle are Vega nearly overhead in the east, and Deneb high in the east-northeast. Altair is the nearest of the three at a distance of 16.7 light years away. One light year is nearly 6 trillion miles. Altair is 10 times the brightness of the Sun. If seen at Altair’s distance, the Sun would only be as bright as one of the two stars that flank it. What is rather different about Altair is its rapid rotation. While it’s almost twice the sun’s diameter, it rotates once in about 9 hours, The CHARA Interferometer at Mt. Wilson has actually imaged its squashed disk in the infrared. Our Sun’s a slow poke, taking nearly a month to rotate once.
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: 07/28/2025 – Deneb, a truly brilliant star
This is Ephemeris for Monday, July 28th. Today the Sun will be up for 14 hours and 48 minutes, setting at 9:12, and it will rise tomorrow at 6:26. The Moon, halfway from new to first quarter, will set at 11:06 this evening.
This evening when it gets dark enough the bright star Deneb in Cygnus the swan will be high in the east-northeast. Deneb is the dimmest star of the summer triangle. Of the other stars of the triangle, Vega is higher in the east, while Altair is lower in the southeast. Deneb’s apparent magnitude, or brightness as seen from Earth, is deceptive. Its vast distance of possibly 2,600 light years is over 100 times the distance of Vega. If brought as close as Vega, Deneb would be almost as bright as the quarter moon. It is possibly as bright as 200 thousand Suns; and a huge star, possibly as large as half the diameter of Earth’s orbit. For all this, it is only 19 to 25 times the mass of the Sun.
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: 07/25/2025 – Star Party tomorrow night
This is Ephemeris for Friday, July 25th. Today the Sun will be up for 14 hours and 54 minutes, setting at 9:16, and it will rise tomorrow at 6:22. The Moon, 1 day past new, will set at 10:09 this evening.
Weather permitting, the Grand Traverse Astronomical Society and the Park Rangers will host a star party at Sleeping Bear Dunes National Lakeshore, at the Dune Climb tomorrow night, starting around 9:00 PM. The parking lane closest to the dune will be blocked off for telescopes. Note… the start time is before actual sunset, however the brighter stars will be visible by 9:45. Also on tap will be binary stars, an interesting treat through the telescope. Then, as it gets darker some of the brighter interstellar wonders will appear. The Rangers leave around 11:00 PM however if it stays clear and there’s enough interest, society members with their telescopes will stay longer. Another star party is planned at the Dunes this summer, on August 23rd.
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: 07/24/2025 – Vega, nearing the zenith in the evening now
This is Ephemeris for Thursday, July 24th. Today the Sun will be up for 14 hours and 56 minutes, setting at 9:17, and it will rise tomorrow at 6:21. The Moon is new today, and won’t be visible.
Vega, in the constellation Lyra the harp, is the highest bright star In the east and brightest star of the Summer Triangle also rising in that direction. It is an important and much studied star, first as a standard for brightness for the magnitude scale at almost exactly zero. In 1983 the Infrared Astronomy Satellite, IRAS, discovered an excess of infrared radiation coming from the star. It seems now that there are two orbiting rings around the star, an inner warm ring and an outer cold ring. This is somewhat like the two disks of material the Sun has: The asteroid belt between Mars and Jupiter and the Kuiper belt, beyond Neptune. No planets have yet been discovered around Vega, but I wouldn’t bet against it.
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: 07/23/2025 – Our weekly look at the whereabouts of the naked-eye planets
This is Ephemeris for Wednesday, July 23rd. Today the Sun will be up for 14 hours and 58 minutes, setting at 9:18, and it will rise tomorrow at 6:20. The Moon, 1 day before new, will rise at 5:43 tomorrow morning.
Let’s take our weekly look at the whereabouts of the naked-eye planets. The Red Planet Mars, will be seen low in the western sky at 10:30 PM. Mars is moving toward Spica, higher in the southwest. It will pass above Spica on September 12th. Mars moves much faster against the background stars than the more distant Jupiter and Saturn. Speaking of Saturn, it now rises just before midnight at just about due east, and by 5:30 AM will be high in the south. Venus will rise at 3:25 AM in the east-northeast and will be higher in that general direction by 5:30. Jupiter will be below and left of it then. That they will appear among the winter stars will become more apparent in the next few weeks.
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: 07/22/2025 – It’s Pi Approximation Day!*
* I’d want to call it “Pi Fractured Fraction Day.”
This is Ephemeris for Pi Approximation Day, Tuesday, July 22nd. Today the Sun will be up for 15 hours exactly, setting at 9:19, and it will rise tomorrow at 6:19. The Moon, 2 days before new, will rise at 4:27 tomorrow morning.
So why is July 22nd Pi Approximation Day? Pi being the Greek letter that represents, mathematically, the ratio of a circle’s diameter to its circumference. Well, we had Pi Day on March 14th or 3.14. Today represents the fractional way of getting to Pi, twenty-two sevenths for July 22nd. In Europe, it’s 22/7, rather how we in America write the date 7/22. I’ve never approximated pi that way. It’s one of those dreaded fractions I learned about in grade school, and to boot it’s an improper fraction. The Bible has a thing for the numbers 7, 40 and a thousand. Also, pi being equal to three. In First Kings, chapter 7, verse 23 it talks about a vessel with a diameter of 10 cubits and a circumference of 30 cubits. A very rough approximation.
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: 07/21/2025 – When our knowledge of the size of the universe expanded
This is Ephemeris for Monday, July 21st. Today the Sun will be up for 15 hours and 2 minutes, setting at 9:20, and it will rise tomorrow at 6:18. The Moon, 3 days before new, will rise at 3:18 tomorrow morning.
A little over 100 years ago astronomers the Milky Way and the surrounding stars were thought to be the entire universe. A universe which was, apparently, disc shaped. Astronomers photographed examples of objects they called spiral nebulae, which they thought belonged to the Milky Way. Then Edwin Hubble photographed stars in the Andromeda spiral nebula. One star changed brightness in a way like some of the stars we know in our Milky Way. These stars are called Cepheid Variables and the rate of variation in brightness is related to their true brightness. This star that Hubble found was much too dim and much too far away to be in the confines of the Milky Way. Soon we found that we are in a spiral nebula or galaxy, like billions of others.
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
Left: Carnegie Observatories. Right: NASA, ESA, and the Hubble Heritage Team (STScI/AURA); Acknowledgment: R. Gendler
The universe “expanded” again, when astronomers found out there were two types of Cepheids, one 4 times brighter than the other. Using the brighter Type I Cepheids, the measurement doubled the estimated distance*. This was about the time in the early 1950s when I was getting interested in astronomy, so the quoted distance to Andromeda and all the other galaxies doubled from older astronomy books to the newer ones.
* Inverse square law: brightness drops with the square of the distance. Double the distance and the brightness drops by 22 or 4.
Ephemeris: 07/18/2025 – The summer Milky Way is beginning to make itself seen
This is Ephemeris for Friday, July 18th. Today the Sun will be up for 15 hours and 8 minutes, setting at 9:23, and it will rise tomorrow at 6:15. The Moon, 1 day past last quarter, will rise at 1:07 tomorrow morning.
The summer Milky Way is beginning to make itself seen. It runs from the north northeast through the sky in the east, and through the stars Deneb and Altair of the Summer Triangle down to the south-southeastern horizon. One has to stay up to 11 PM or later to actually enjoy it. Another prerequisite is that one has to be away from the city lights. Here in Northern Michigan we have a lot of dark skies and only small towns, so it is easy to get away from city lights. To the ancients and relatively primitive cultures without the curse of the electric illumination, it was a wonder. In Greece, Rome and Egypt it was a milky stream, from which we get the term Milky Way. Some cultures considered it the path that souls took after death on their journey to the hereafter.
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
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