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PostPosted: Sat Jan 14, 2017 1:50 pm 

Joined: Thu Jun 02, 2016 11:32 am
Posts: 430
Location: New Farnley, Leeds lat 53.8N long 1.6W
Astronomy is a fruitless pursuit, full of frustration. Why bother? Stars are hard to find in the dark because it’s not dark anymore. Because of city lights. Because of insecurity lights. Because of photomaniac neighbours and their Disneyland gardens. Try observing an eclipse of the binary star RZ Cassiopeiae. If you can overcome the frustration of trying to spell it correctly.
Use 15x70 binoculars on a photo tripod with a counterweight dangling under it (trust me, you’ll need the stability). This is good kit for estimating variable stars and I promise that it will give you hours of swearing fun in the backyard. Settled in a folding chair on the dim lawn, tripod adjusted to a convenient height and, with eyes gently brushing the rubber eyecups you concentrate with quieted breath on that looming star speckled portal and … Chair crashes sideways, tripod and binoculars rattle off into the murk, shocked observer rolling on the wet grass, swearing. Cats are delighted to keep their loved ones company in the quiet of the night by leaping nimbly from a garage roof onto shoulders. Yes, it happened to me and similar things will happen to you, I hope.
Anyway, I digress. Here is RZ Cassiopeiae. Primary eclipses last for about 4.8 hours and its brightness falls from visual magnitude 6.4 to 7.8 every 29 hours, allegedly. First find a prediction for an eclipse that I can follow to the end. One of the interesting things about RZ Cas is that the interval between its eclipses shifts over time because … well, like our cataclysmic feline and observer pair, it’s a dynamic system. So, I find what is hopefully a reliable prediction for mid-eclipse, minus 2.4 hours to catch the start, If it’s not cloudy.
I cart my kit outside, burdened by a leaden anxiety for the accuracy of that eclipse prediction and the worry that all my estimates might be a shambolic illusion. Oh get on with it! Where’s that chart field? Yay! I find it, neck crickingly overhead. I am crouched in the driveway like an arthritic crab with a death grip on the binoculars that is making the stars giggle so much that it’s impossible to make a brightness estimate. More swearing in the half dark.
Il faut s’adapter, as the crabby old French saying goes. So I prod a tripod leg onto the neighbour’s wall to gain height and it actually works tolerably well: the stars stop giggling at me and I make estimates every 15 minutes or so. Read them from left to right.
17.20 mag 6.4 17.35 mag 6.4 17.51 mag 6.5 (it’s started!) 18.06 mag 7.0
18.21 mag 7.1 (getting misty) 18.37 mag 7.5 (foggy) 18.55 mag 7.5 (fog)
19.08 mag 7.6 (neighbour’s bathroom light – why does she always wee on my variables?)
19.45 mag 7.0 (haze, what’s happening? It should be at minimum)
19.56 mag 7.2 (that’s too bright. More mist)
20.13 mag 6.4 (impossible, the eclipse can’t have finished yet, more mist)
20.30 mag 6.5 (weird, more mist)
20.47 mag 7.2 (what’s going on? Two eclipses?? Clear sky) 21.03 mag 6.8 (clear)
21.19 mag 6.7 (light mist) 21.41 mag 6.6 (light mist) 22.02 mag 6.4 (clear).

What a mess. It can’t vary like that. I might as well chuck this away. Why bother? Then it dawns on me that between about 19.45 and 20.30 mischievous mists must have played cat and mouse with my northernmost comparison stars, making RZ appear anomalously bright then.
Finally, I send my annotated estimates to the Section Director who will conclude that here is evidence of some further change in the period of RZ Cassiopeiae. More likely when compared with other observations, the SD will realise, that whatever these numbers are, they have nothing to do with RZ Cas!
Ah well, as that great alchemist Isaac Newton ought to have said, “Natural Philosophae is an applecart that even ye catte might upset”.

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PostPosted: Sun Jan 22, 2017 8:11 am 

Joined: Sat Sep 24, 2016 10:16 pm
Posts: 14
Congratulations to Bob for persisting and observing most of this eclipse of RZ Cas and for working out why some of his observations appeared discordant.

Observing the whole of an eclipse can be a challenge and over the course of a year I manage to observe relatively few whole eclipses. There are various reasons for this - the sky will cloud over, the eclipse might start or end during twilight, the star may not have risen when the eclipse starts or may set before the eclipse ends ... and even for circumpolar variables, there can be gaps when they are lower in the sky and disappear behind trees or nearby buildings!

Fortunately it is possible to combine observations made of parts of different eclipses in order to combine a whole eclipse. Hence it is always worth reporting your observations even if you didn't see the whole eclipse.

The SPA VSS light curve for RZ Cas in 2016 is included in the section's annual report, which can be viewed here:

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