The September equinox is a significant season for stargazers even though it does not offer a specific visual spectacle. It marks the start of astronomical fall in the northern hemisphere and astronomical spring in the southern hemisphere, creating an equal balance of day and night. To enhance celestial observations, here's a comprehensive guide for observing the moon, planets, stars, and more this week.
The Moon and the Night This Week
The first on the list that stargazers should look forward to is the crescent moon and "Earthshine" on Monday, September 18. On the southwest just after sunset, 14% of the moon will be illuminated, giving a crescent appearance.
In the absence of neighboring planets that have frequently accompanied it this year, turn your attention to the enchanting phenomenon known as "Earthshine." This radiant effect results from sunlight traveling from the sun, reflecting off Earth's vast oceans and ice, and then gently illuminating the moon's dark side.
On Wednesday, September 20, stargazers can still see the crescent moon. As night descends, look to the western sky, where a 31% waxing crescent moon will grace the celestial canvas. It will be in close proximity to Antares, a colossal star with a mass 12 times that of our sun, nestled within the Scorpius constellation.
This brilliant luminary ranks fifteenth in brightness among the stars and, if it were part of our solar system, would nearly reach the orbit of Jupiter.
By Friday, September 22, the first quarter moon and Mercury will be visible. As the moon reaches this phase, presenting its near-side to Earth, revealing a half-illuminated appearance. However, this phase signals a challenging time for stargazers as the waxing gibbous moon's luminance increasingly washes out the night sky, making it more challenging to observe stars and faint celestial objects.
This day also offers one of the prime opportunities in 2023 to spot Mercury, albeit requiring binoculars and an early rise. Roughly 30 minutes before sunrise, Mercury will grace the horizon, appearing approximately 10º above it-an impressive height for the closest planet to the sun.
Lastly, the autumnal equinox will happen at 2:50 a.m. EDT on Saturday, September 23. The equinox will mark the precise moment when the midday sun crosses the equator at some point on Earth's surface.
More About the September Equinox
Two equinoxes occur annually, in September and March. The September equinox signifies the Sun's transition across the celestial equator, typically falling on September 22, 23, or 24 in most years, as it moves from north to south. Here are the top 10 facts about this changing of seasons:
- Second Equinox of the Year: The September equinox occurs around September 22, while the first equinox, the March Equinox, happens around March 21 annually.
- Transition to Autumn (Northern Hemisphere): The September equinox marks the beginning of astronomical fall (autumn) in the Northern Hemisphere, signifying the end of summer. Meteorological fall starts on September 1 and ends on November 30.
- Welcome Spring (Southern Hemisphere): In the Southern Hemisphere, the September equinox is the vernal (spring) equinox, considered the first day of spring by astronomers.
- Momentary Event Equinoxes: These are brief instances when the Sun crosses the celestial equator, aligning Earth's axis neither toward nor away from the Sun. In 2023, this occurs on September 23 at 06:50 UTC, shifting to September 22 in locations 6 hours and 50 minutes behind UTC.
- Variable Date: The September equinox typically falls on September 22 or 23, rarely on September 21 or 24. The last September 24 equinox was in 1931, the next in 2303. This variation arises from the discrepancy between the Gregorian calendar year (365 days) and Earth's actual orbit time (about 365 and 1/4 days).
- Equal Day and Night: The term "equinox" originates from Latin, meaning "equal night," but it doesn't guarantee precisely 12 hours of daylight and night worldwide.
- Not All Places Gets Equal Night and Day: Most places receive more than 12 hours of daylight on the September equinox due to factors like sunrise/sunset definitions and atmospheric refraction.
- Shorter Time: Between Moonrises Around the September equinox, the Harvest Moon rises more closely together, deviating from the usual 50-minute daily increase in moonrise times.
- Northern Lights Opportunity High: Northern Hemisphere latitudes have an increased chance of witnessing the aurora borealis (Northern Lights) during the September equinox, as geomagnetic activity is more likely in spring and fall.
- Global Celebrations: Cultures worldwide commemorate the September equinox with feasts, festivals, and holidays.
RELATED ARTICLE: Equinox: The Light and Darkness Phenomenon That Happens Twice a Year
Check out more news and information on Equinox in Science Times.
