September 5, 2022: Watch Mars continue its eastward march through Taurus before sunrise. Watch the Harvest Moon Effect during the next several evenings. Later in the evening the moon occults a star in Sagittarius.
by Jeffrey L. Hunt
Chicago, Illinois: Sunrise, 6:21 a.m. CDT; Sunset, 7:17 p.m. CDT. Check local sources for sunrise and sunset times for your location.
The Harvest Moon occurs at 4:59 a.m. CDT on the 10th. This full moon is likely the most famous of the year’s nicknamed moons. It is named for the full moon closest to the autumnal equinox that occurs on the 22nd. Traditionally and before the invention of artificial illumination, the bright moon assisted farmers in their fields after sunset.
Besides the name that corresponds with the season, there is a Harvest Moon Effect. This occurs when the moon is approaching the vernal equinox.
The equinoxes and solstices are specific days related to the sun’s position compared to an imaginary heavenly globe that is perceived to hold the sun, moon, stars, and planets – the celestial sphere. It is not real, but a convenient means of describing the sky.
The celestial globe has a coordinate system that is similar to earth’s longitude and latitude coordinates. It starts with the celestial equator, a circle on the globe directly above the earth’s equator. The sky has celestial poles as well, designated north and south. Polaris is near the north celestial pole, and so, it nearly stands above the north cardinal point.
Because of Earth’s tilt, the plane of the solar system is tilted 23.5° compared to the celestial equator. The ecliptic crosses the celestial equator at two spots – the equinoxes. The summer solstice is the point farthest north of the equator and the one farthest south is the winter solstice, as defined from the northern hemisphere. The vernal equinox is the name of the origin of the coordinate system (the 0°, 0° point). All coordinates are measure from this spot in the sky.
When the sun has the origin’s coordinates, the day is known as the Vernal Equinox, a date on the calendar. The same occurs for the other celestial points.
The autumnal equinoxes is opposite the vernal’s coordinates, making the autumnal’s coordinates 180°, 0°). The longitude is normally expressed in hours and minutes, like time, and named right ascension. The latitude, known as declination, is measured in degrees, like that on a protractor.
At the Vernal Equinox, the sun sets at the west cardinal point. Half the sky away (180°), the vernal equinox is at the east cardinal point.
The tilt of the solar system from the east horizon is near its minimum. As the moon moves eastward each day, approximately 13°, it moves somewhat parallel to the horizon. When the sun is near the autumnal equinox, the moon is approaching the vernal equinox and the full phase in the east.
The average delay of moonrise from day to day is about 53 minutes. During a 24-hour period, the moon rises later from its eastward motion. The average does not reveal much about the shortest times.
In the table below, the dates are listed for several days during September 2022. The moonrise time in standard time – add one hour for daylight time – is listed for each day. This data is from the U.S. Naval Observatory (USNO). The delay of moonrise is calculated simply by subtracting the day’s moonrise time from the previous day’s time.
For example, on the 8th, the delay is 35 minutes from subtracting moonrise on September 7 from moonrise on September 8. (Be careful subtracting times. It might be necessary to borrow an hour to add 60 minutes to the minutes part.)
The next column lists sunset times in standard time. Again, the data is from USNO.
The last column is the difference in time from moonrise to sunset. When moonrise occurs before sunset the less than symbol (<) is used. When it’s after sunset, the greater than symbol (>) is used.
This year as the date of the full moon nears, the delay of moonrise quickly diminishes, reaching minimum values of 23 minutes on the 11th and 12th. Then it begins to increase again.
But notice the difference in moonrise and sunset. From the 7th to the 9th, the bright moon is already in the sky at sunset and then darkness takes over. It’s a challenge to see much detail on the ground after about 45 minutes after sunset.
Beginning on the 11th, the moon rises nearly an hour after sunset when the sky is pretty dark. So there is a gap between the brightest twilight and moonrise.
|Date (2022)||Moonrise (CST)||Delay from previous day||Sunset (CST)||Moonrise/Sunset|
|Sep 5||15:34||1:05||18:17||< 2:43|
|Sep 6||16:29||0:55||18:16||< 1:47|
|Sep 7||17:13||0:44||18:14||< 1:01|
|Sep 8||17:48||0:35||18:12||< 0:24|
|Sep 9||18:17||0:29||18:10||< 0:07|
|Sep 10||18:42||0:25||18:09||> 0:33|
|Sep 11||19:05||0:23||18:07||> 0:58|
|Sep 12||19:28||0:23||18:05||> 1:23|
|Sep 13||19:52||0:24||18:03||> 1:49|
|Sep 14||20:18||0:26||18:02||> 2:16|
The effect of short delays for moonrise occurs whenever the celestial sphere’s vernal equinox is near the east horizon and the moon is approaching it, regardless of the time of night, season, or moon phase. All lunar phases experience this short delay of moonrise – the Harvest Moon effect. This time of the year culturally we note the Harvest Moon, although few of us in North America need moonlight to complete our work.
Here are planet highlights for today:
Mars is the bright star in high in the southeast before sunrise. It maintains its eastward march through Taurus, above the Hyades cluster and Aldebaran, the Bull’s head.
Use a binocular to spot Mars and the Hyades star cluster. This morning the Red Planet is 1.3° to the upper left of Epsilon Tauri (ε Tau on the charts). Visualize the Bull’s head as a letter “V.” Aldebaran is at the top of the left side of the letter and Epsilon is at the top of the right side.
Move the binocular slightly to include Kappa Tauri (κ Tau) and Upsilon Tauri (υ Tau). Mars passes between Upsilon and Epsilon this morning.
In two mornings, Mars passes Aldebaran. Spot the changing spot of the planet each morning.
During morning twilight, Jupiter is about one-third of the way up in the southwest.
In comparison, Venus keeps rising later, appearing low in the east-northeast as morning twilight grows.
One hour after sunset, the waxing gibbous moon, 75% illuminated, is less than one-third of the way up in the south in the Teapot’s handle, part of Sagittarius. The lunar orb is near the star Tau Sagittarii (τ Sgr on the chart). About 10:30 p.m. CDT, from Chicago, the moon covers or occults the star. This occultation is visible across the U.S., Mexico, Central America and southern Canada. Use a binocular or spotting scope to watch the star disappear behind the moon, then reappear about an hour later, depending on the location.
Early in the evening, Saturn is in the southeast at about the same altitude – height above the horizon – as the moon. Two hours after sunset, bright Jupiter is low in the east, followed by Mars nearly two hours later. After midnight, the moon is low in the west, Saturn in the west south west, Jupiter toward the south, and Mars in the eastern sky.