Bob Moler's Ephemeris Blog

This is Ephemeris for Tuesday, August 12th. Today the Sun will be up for 14 hours and 10 minutes, setting at 8:52, and it will rise tomorrow at 6:43. The Moon, 3 days past full, will rise at 10:26 this evening.

Tonight we get a second chance to see some of the Perseid meteor shower. As I said yesterday, the Moon is going to interfere with this year’s display. But, there is a small interval during twilight this evening, before the moon rises, where the sky could be dark enough to see more than a few Perseids. For nearly half an hour after 10 PM, it might be dark enough to see the Perseids under reasonably dark skies. The radiant where the meteors appear to come from will be low in the north northeast, about 17° above the horizon which means the expected number of meteors one would see in a half hour would be about 15 and with a not quite dark skies probably be a little less than that. But it is a chance to see the Perseids this year.

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

This is Ephemeris for Tuesday, August 6th. Today the Sun will be up for 14 hours and 25 minutes, setting at 9:01, and it will rise tomorrow at 6:36. The Moon, 2 days past new, will set at 10:15 this evening.

Next Monday morning we’ll see the peak of the Perseid meteor shower. They’re called the Perseids because they seem to come from the constellation of Perseus the hero which is below the W shaped constellation of Cassiopeia in the northeast in the evenings now. The reason they appear to come from the same direction is that they were shed by a comet whose name is Swift-Tuttle discovered in 1862 it’s been around many times before that, though not recognized as such. The first mention of the Perseids in history comes from the year 36 CE, though they were assuredly visible but unrecognized before that. In the past they’ve been known as the Tears of Saint Lawrence because their peak is near the feast date of that martyr. Perseids can be seen now, though not in peak numbers.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT–4 hours). Times will be different for other locations.

Addendum

This is Bob Moler with Ephemeris for Thursday, August 10th. Today the Sun will be up for 14 hours and 17 minutes, setting at 8:56, and it will rise tomorrow at 6:40. The Moon, 2 days past last quarter, will rise at 1:43 tomorrow morning.

Back before astronomers recognized the major meteor shower that occurs at this time of year, the streaks of light in the sky of “falling” or “shooting” stars were called, by Christians, the Tears of Saint Lawrence, who was martyred on this day in the year 258. The bits of comet debris, ranging from the size of sand grains to that of a pea, hit our atmosphere at 38 miles (59 kilometers) per second and quickly vaporize due to friction, causing the streak of light we call a meteor. They are called the Perseids since they appear to come from the constellation of Perseus, located in the northeastern sky. They will be best seen Saturday night and into Sunday morning, with rates of up to one a minute, on average, especially in the early morning hours.

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

The Dome of the sky for the night of August 12th and 13th, 2023 at 10:30 PM for northern Michigan. The Perseid radiant is in the northeast and fairly low in the sky, and marked in yellow with the caption PerR. It will continue to rise in the northeast throughout the night. The constellation names are abbreviated. Their full names can be found here. Large images can be truncated on the right. Click or tap on the image to enlarge and display the complete image. Created using my LookingUp app.

The Dome of the sky for August 12th and 13th, 2023 at 3 AM for northern Michigan. The Perseid radiant is in the northeast, much higher in the sky, and marked in yellow with the caption PerR. The constellation names are abbreviated. Their full names can be found here. Large images can be truncated on the right. Click or tap on the image to enlarge and display the complete image. Created using my LookingUp app.

Remember, the meteors only seem to come from the radiant. They will appear all over the sky! The meteors of a shower travel in parallel paths, like train tracks, disappearing to a point in the distance.

This is Ephemeris for Thursday, August 12th. Today the Sun will be up for 14 hours and 10 minutes, setting at 8:52, and it will rise tomorrow at 6:43. The Moon, 3 days before first quarter, will set at 11:13 this evening.

It’s not too late to see the Perseid meteors. The projected peak of the shower is expected to be between 3 and 6 this afternoon. So the meteor shower should still be quite active. It has been my experience that the numbers of meteors decline more rapidly than they increase before the peak. NASA can determine their orbits using all sky cameras placed at different locations to get their paths by triangulation. The cameras have shutters the interrupt the meteor track at a specific interval, which allow them to determine the meteor’s speed and are able to calculate the particle’s orbit of the Sun. An animation of these orbital tracks can be found on the International Meteor Organization website imo.net.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT – 4 hr). They may be different for your location.

Addendum

I’ve been talking about the Perseid meteor shower all week, so far. Click on the calendar dates to the upper right to review those posts.

A Perseid outburst from 2009. Credit NASA/JPL via Phil Plait’s Bad Astronomy.

Perseid fireballs in one of NASA’s all sky cameras during the morning hours of August 13, 2017. This is a long time exposure. The bright swath in the image is the Moon that morning. Since it is a time exposure, the radiant is also moving with the earth’s rotation, so the meteors only seem to come from the northeastern sky. North is at the top, and East is to the left. Credit NASA.