This time of year

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William Bottaci

May 24, 2021, 1:22:24 PM5/24/21
We have now entered astronomical twilight for the next 2 months, putting a damper on visual observing and imaging, for the deepsky objects at least. Looking outside this evening I could tell, from the rain and maximum temperature of 11°C...

For any serious imaging, assuming say 2 hours of exposure, these 2 months expands by about a week either side, and even then you're limited to between 1 am to 3 am. A lot depends on the direction - clearly towards the north would not be as good as towards the south; it's not even across the sky. Then you have to factor in any light pollution, moonlight etc.

As it's much about contrast then star clusters would be better objects than nebulae and galaxies, but objects low in the south have a short window and are well placed at this time of year. Even so, with digital cameras and processing we've still seen many worthwhile images in less than ideal conditions.

This does not affect the Moon, but to add to the depressing news the lunar eclipse in 2 days time (the totality only just happens) is not visible from anywhere close to Europe.

On a lighter/brighter note, the Sun is featuring a reasonable sized sunspot right now, and visible from all round the world.

Related, it's well known that the centre of gravity of the solar system is not directly in the centre of the Sun but at the barycentre, but it's not often realised that due to the distances to the major planets this barycentre is often outside the Sun, so from a fixed viewpoint above the solar system the sun appears to wobble; especially when Jupiter and Saturn are close together, as was last year, and even better when Uranus and Neptune are also nearby them.
Attached is a 522 year run from actual data, from 1500 CE to 2022 CE (or 1500 AD to 2022 AD in old money).

The relation, besides it being the Sun, is that Jupiter and Saturn line up about every 20 years, and we all know what that is close to... (22 year sunspot cycle).
Disclaimer: The sunspot cycle mechanism is still a mystery but also there's no hard evidence these two planets have anything to do with it. Still, plenty of wriggle room for pseudo scientists then!


=SS barycentre 520 years.jpg (70K)=
SS barycentre 520 years.jpg
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