CAS Sky Notes for September 2023

The nights are drawing in fast now and if the cloud ever breaks you should get some observing done!


Mercury:  Mercury reaches greatest Western elongation of 18° on the 22nd and so is a morning object.  It has a more northerly declination and so may be visible if you have a clear eastern horizon before dawn.

Venus:  Venus is now an easy morning object. It starts the month as a thin crescent (about 15%), but increases to a thick crescent (35%) by the end of the month, by which time it will have an elongation of 43° and very well placed.

 Mars is still technically visible in the evening sky, but is very difficult as it sets soon after the Sun.  It approaches conjunction in November.  On the 16th Mars passes 0.7° south of the Moon.

Jupiter is now rising around 9 pm by the middle of the month and 8 pm by the end. It is very bright low in the south east by late evening. 

Saturn reached opposition at the end of August and is visible all night.  It is low in the sky, but is well worth viewing.  The rings are at a shallow angle. 

Uranus is not far from Jupiter (in the sky – not in reality!) and so is becoming easier to find.  I will send out instructions to find it later in the month. 

Neptune reaches opposition on the 19th and so is well placed.  Contact your Coordinator if you want ephemeris to find it.

The Sun

Solar activity is still increasing and solar observations are a good idea.  Take great care to never look directly at the Sun, or directly through an optical instrument.

Ensure a proper filter is in place or project the image onto card. 

Meteor Showers:  The Eta Perseid meteor shower reaches a maximum on the 10th September but may be seen through the middle of the month.  The ZHR (Zenith Hourly Rate) is only around 5 though, so be patient!


6th September:     Moon is at Last Quarter     15th September:  New Moon

22nd September:  Moon is at First Quarter    29th September:  Full Moon


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