2024 August 18

OBSERVERS CHALLENGE: A LUNAR OCCULTATION OF SATURN ON 2024 AUGUST 21

Mike Foulkes

(Image by Dave Tyler)

A lunar occultation of any of the bright planets is an interesting event to watch even though they are rare. Such an occultation of Saturn will take on August 21 and is favourable for observers in the UK. However this occultation occurs during the early hours of the morning, requiring staying up late or getting up early in order to observe this event. The Moon will be just over a day past full. The planet and its satellites will disappear at the bright limb of the Moon and then reappear at the dark limb. Reappearance will occur twilight.

Predicted mid-event timings for this event for both Greenwich (London) and Edinburgh are given in the 2024 BAA handbook. For Greenwich the planet disappears at 03:28.7 UT and reappears at 04:21.2 UT. For Edinburgh, the planet disappears at 03:33.5 UT and reappears at 04:09.8 UT.

The disappearance and reappearance positions for both of these locations are shown in the figure below.

Figure showing the locations of disappearance (D) and reappearance (R) for Greenwich and Edinburgh. These Images were derived from Stellarium.

However the times and positions of the disappearance and reappearance depend on the geographical location of the observer. For example, the duration of this event for observers in the far north of Scotland will be much less. Consequently, observers are recommended to find the exact circumstances of this event for their own location using software such as Stellarium or WinJUPOS. The use of such software will also allow the identification of a suitable reference feature on the lunar terminator to act as a guide to the reappearance of Saturn on the dark limb.

The inclination of the rings with respect to the Earth will be just over 3 degrees. With such a low ring inclination, the major satellites will appear in a rough line with the rings. The positions of the brighter satellites at the time of the start occultation are shown below. The brightest satellite, Titan, will be preceding Saturn at the time of the occultation. It will therefore be occulted before Saturn and then reappear at the dark limb also before Saturn.

The positions of the brighter satellites of Saturn at the time of the occultation. North is up. This image was derived from Stellarium.

It is likely that these satellites may be difficult or impossible to detect during the disappearance at the bright limb. However it will be interesting to see if at least Titan can be detected at or after reappearance.

There will be a noticeable brightness difference between Saturn and the Moon; particularly at the bright limb. This will impact on the exposures used for those who wish to take close-up images of this event. During previous occultations, some observers have generated composite images to record the event.

If you are able to observe this occultation, please post your observations on the BAA observation gallery or send them into the Saturn, Uranus and Neptune Section.

Mike Foulkes. Saturn, Uranus and Neptune Section Director.