The starry sky in September 2023
The nights are now long enough. From now on, the observatory will again be offering public observation evenings on Friday evenings from 9 pm, provided the night sky is cloudless. A ticker on the main page will provide information on the current status from noon on Friday at the latest.
SUN AND MOON
We are approaching the equinox again. The sun reaches its autumn point this year on the 23rd at 8:50 am. The length of day and night are identical at this time.
If the sun rises over Zweibrücken at 6:42 a.m. on the 1st, this shifts to 7:25 a.m. on the last day of the month. Sunset is correspondingly earlier from 8:17 pm to 7:15 pm.
The full moon still disturbs the view of the sky in the first few days of the month and then again around the 29th.
Jupiter is close to the moon, which is no longer completely full, on the 4th of the month. The distance is 3.1 degrees at 11 pm. On the 27th at 3 am, the distance between Saturn and the Earth's companion is 2.7 degrees.
PLANETS
After the middle of the month Mercury the second morning visibility this year. From the 19th, the difficult-to-observe planet can be seen in the eastern sky from around 5:40 am. On the 22nd, the small disk will be half illuminated.
Earth's somewhat smaller sister planet, the Venus, moved from the evening to the morning side in the previous month and is now rapidly moving away from the Sun. It shines at its brightest on the 3rd.
Mars cannot be observed for the rest of the year, it is in the daytime sky.
Jupiter begins its opposition period on the 4th, which is also noticeable in its increasing brightness. In the middle of the month, it crosses the horizon at 21:30.
The Lord of the Rings, the Saturnwas in opposition to the Sun at the end of the previous month. Due to its position in Aquarius, it does not reach a great height on the horizon. The inclination of the ring at this year's opposition is also only 9 degrees, which still makes it an impressive object. The next view of the edge of the ring will be in March 2025.
On 27 August, the distance from Earth was 8.76 astronomical units, which corresponds to 1310 million kilometers. Even in smaller telescopes, the planet's oblateness of 1:9 is clearly visible. This is due to its high rotational speed.
The sidereal rotation period, i.e. the rotation by exactly 360 degrees, is between 10h 32min and 10h 47min. The first rotation period was measured by the Voyager probes in the early 1980s, the second by the Cassini probe in 2004 and still presents scientists with a mystery as to the cause. It is assumed that this phenomenon is caused by the changing flow conditions of the atmospheric layers.
It rises at 20:01 at the beginning of the month and moves further ahead to 18:03 at the end of the month.
STARRY SKY
The summer triangle has already shifted noticeably to the west. The autumnal quadrilateral, consisting of four bright stars of Pegasus, is already making its presence felt in the eastern sky.
One object for binoculars is the magnificent globular star cluster M13 in faint Hercules, which can still be seen in the western sky in the evening this month. It is located between the constellations of the Swan and the near-horizon Bear's Keeper or Bootes.
The following graphic shows the view of the sky on September 15 at 11 pm.
