THE SOUTHWORTH PLANETARIUM

70 Falmouth Street      Portland, Maine 04103

(207) 780-4249      usm.maine.edu/planet

43.6667° N    70.2667° W 

Founded January 1970

2022-2023: VIII

Sunrise: 6:13 a.m.

Sunset: 7:04 p.m.

Civil twilight ends: 7:33 p.m.

Sun's host constellation: Leo the Lion

Moon phase: Waxing gibbous (91% illuminated)

Julian date: 2459831.16

"I lived long enough to know that things never remain quite the same for very long."

-Queen Elizabeth II

THE DAILY ASTRONOMER Thursday, September 8, 2022

September 2022 Night Sky Calendar Part III

THURSDAY, SEPTEMBER 22: AUTUMNAL EQUINOX (GOLD EVENT!!!)

At 9:03 p.m. today astronomical autumn begins in the northern hemisphere while astronomical spring begins in the southern hemisphere. Today the Sun will rise due east and set due west. (The same will be true on the vernal equinox in March.)

The four seasonal dates for 2022 are as follows:

• SPRING March 20, 2022
• SUMMER June 21, 2022
• AUTUMN Sept 22, 2022
• WINTER Dec 21, 2022

Notice something about that list? The Autumnal equinox doesn't occur on the 20th or 21st. That is not unusual. The Autumnal equinox hasn't occurred on September 21st for more than a thousand years.* Why does the autumnal equinox occur on a later date in September than the other seasonal dates occur in their respective months? Simple. Astronomical summer is the longest season in the northern hemisphere. To understand why, we must discuss the reason we experience seasons.

We have seasons because Earth is tilted by about 23.5 degrees relative to the vertical. As Earth revolves around the Sun, the Northern Hemisphere is alternately oriented toward and then away from the Sun. Consequently, the Sun's altitude varies with the changing orientation: higher in the spring and summer; lower in the autumn and winter. During the spring and summer, the Sun remains above the horizon for more than twelve hours and its higher angle enables it to heat us more efficiently than it does in the autumn and winter.



If Earth's orbit were perfectly circular, our planet would require the same amount of time to progress from one seasonal point to another.  However, the orbit is elliptical, so Earth's distance from the Sun varies continuously and so, too, does its orbital speed. (The closer a planet moves toward the Sun, the faster its orbital velocity will be.) Earth is closest to the Sun (perihelion) between January 1-4 and at its greatest distance (aphelion) around July 2-4. As Earth is closest to the Sun during winter, it is moving fastest along its orbit. In the summer, Earth is farther away and therefore its orbital speed is slower. Consequently, the time our planet requires to proceed from the winter solstice point to the vernal equinox is almost 89 days (88.9). The time that elapses between the summer solstice and autumnal equinox is 93.6 days. Our summer is more than four days longer than our summer.  

The season durations:
Winter     88.9 days
Spring     92.8 days
Summer  93.6 days
Autumn   89.85 days  

Just a reminder that we are referring to astronomical winter, not meteorological winter, which is interminable here along the nation's northern tier. We all know that autumn's inception heralds winter's imminent arrival. Of course, the less said about that, the better.

Happy Astronomical Fall everyone!

FRIDAY, SEPTEMBER 23: MERCURY IN INFERIOR CONJUNCTION

The little elusive world moves between the Sun and Earth and so will not be visible. Mercury will now move into the morning sky. (See "Planet Watch")

SUNDAY, SEPTEMBER 25: NEW MOON Beginning of lunation cycle 1234

MONDAY, SEPTEMBER 26: JUPITER AT OPPOSITION

Today, Earth passes between the Sun and Jupiter. When at opposition, a superior planet (one more distant from the Sun than Earth) is generally at its brightest and is also at its least distance. The next opposition of Jupiter occurs on November 1, 2023.

PLANET WATCH

MERCURY The first world lurks low in the western evening sky at month's beginning and then vanishes like a ghost in forest mist by month's beginning. Mercury moves into inferior conjunction on the 23rd and then emerges into the pre-dawn eastern sky in early October. VERDICT: If you must see Mercury, find it before the 10th and then give it a miss until next month.

VENUS

[Host constellations      Early month  -  Leo;  Late month - Virgo]

Always brilliant, but not always easy to find. This dazzlingly bright, yet dreadfully hot planet lingers around the pre-dawn sky throughout the month. Throughout September, Venus will move progressively closer to the Sun. Venus vanishes like, well, like a planet that veers too close to the Sun in the sky, in October. VERDICT: Early risers will want to cast a quick glance toward the "morning star" this month. Even when elusive, Venus never disappoints.

MARS

[Host constellation - Taurus the Bull]

The devil eye planet is growing brighter and drawing ever closer to Earth. Mars rises just after 10:30 p.m. at month's beginning and by 9:45 p.m. at month's end. Watch it move along the "face" of Taurus this month as it moves ever closer to its December opposition date. VERDICT: Though never as spectacular as Venus, Mars still beguiles us with its crimson hue, which is becoming increasingly more distinct as it brightens. If you're up at or after midnight, seek it out in the eastern sky.

JUPITER (PICK PLANET!!)

[Host constellation: Pisces the Fish]

Now, this is the month to find Jupiter! This king world shines brightly in the early evening eastern sky and will remain in sight for most of the night. Jupiter reached opposition on September 26th when it shines 2.5 times brighter than Sirius, the night sky's brightest star. VERDICT: Heavens above, Jupiter is big -well, of course- bright and up all night. What's not to like? Seek it soon after sunset in the east or before sunrise in the west. September 2022 is a fine month for Jupiter admirers.

SATURN

[Host constellation: Capricornus the Seagoat]

Although it's 17 times dimmer than Jupiter, Saturn at least rises first and will be about 30 degrees above the eastern horizon when civil twilight fades. Saturn reached opposition last month, but even then was dimmer than Mars or Jupiter. VERDICT: If you're out looking at Jupiter, just turn your eyes toward the west to see its dimmer gas giant companion Saturn. Although it rarely ever dazzles, Saturn always delights.

*The autumnal equinox will occur on September 21st in 2092 and 2096, just to be difficult.

To subscribe or unsubscribe from the Daily Astronomer:

https://lists.maine.edu/cgi-bin/wa?SUBED1=DAILY-ASTRONOMER&A=1