September 15 – New Moon
The Moon will be in the same direction as the Earth relative to the Sun and will not appear in the night sky. This phase occurred at 08:41. This is the best time to observe faint objects such as galaxies and star clusters, as they will not be affected by moonlight.
September 19 – Neptune in opposition
The giant blue planet will be closest to Earth and will be entirely illuminated by the Sun. It will be brighter than any other time of year and will appear all night long. This is the best time to observe and photograph Neptune. Because the distance from Earth is too far, without powerful telescopes, it will just be a small blue dot in the sky.
September 22 – Mercury reaches maximum western elongation
Mercury reaches a western elongation position, up to 17.9 degrees from the Sun. The best time to view Mercury is when it is highest on the horizon in the morning. Look for the planet in the eastern sky before dawn.
September 23 – Autumn Equinox
The autumnal equinox occurs at 1:43 p.m. The Sun will shine directly on the equator and day and night will be of equal length on the globe. It is also the first day of fall in the northern hemisphere and the first day of spring in the southern hemisphere.
Both hemispheres receive the same amount of sunlight at the autumnal equinox. Photo: Wikipedia.
September 29 – Full Moon, Super Moon
The Moon will be on the opposite side of the Earth to the Sun and its surface will be fully illuminated. This phase occurs at 4:59 p.m. UTC. This full moon was called the Corn Moon by early Native American tribes because corn was harvested at this time of year. This moon is also known as the Harvest Moon. The Harvest Moon is the full moon that occurs each year closest to the September equinox. It’s also the last of three supermoons in 2023. The Moon will be closest to Earth and may appear a little larger and brighter than usual.
See more 2023 ephemeris here: https://deepsky2000.net/lich-cac-su-kien-thien-van-nam-2023