Tony, Walt, Geoff and others,

It seems I have taken 'things' for granted and assumed
it was common knowledge that Antares was a double
star. So appologies all round.

The secondary shines at mag. 5.4 and is 2.5arc seconds
(in PA 273) from the mag. 0.9 Primary star.

Normally the secondary is very hard to see due to the
glare from the primary and so, observing the Antares
pair is a difficult test for a telescope. The scope
needs to have good, clean and well collimated optics,
the tube needs to be well baffled and the air nice and
still to split Antares.... . Probably Sirius/SiriusB
combo is more difficult.

The lunar occultation last Monday AM was an ideal time
to see the secondary while the primary was still
behind the moon's western limb. It was a pity the
moon was 98% full but beggars can't be choosers so I
videoed the event anyway.

Users of WinOccult can reconstruct this event by
entering the following data into their PC...

E.Long. 150 38 27.9 Lat. -33 39 51.9 Alt. 286m.
and doing a search for 14th May

Now, amongst all timing and other stuff you will see
that...
2366 = Antares = alpha Scorpii
2366 is double : 0.9 5.4 2.5" 273.7

also you should be able to find the RV for the event
of .346"/sec. this is the velocity of the star normal
to the surface.

Now the PA of the secondary (273)is very close to the
PA on the lunar limb (287), so the predicted interval
between the r of the secondary and the R of the
Primary can be given by... 2.5"/0.346 = 7.2seconds

So using Geoff's timings
15:41:57.092 = First appearance
15:42:04.572 = First brightening
the observed interval is 7.48 seconds... very close to
the prediction!

That's about all we can say unless somebody else timed
the event. I have heard from Brian Loader that he
observed this event too but I'm unsure if he was able
to extract timings. He did mention the words "blizard"
and "snow" in the same sentence... :-( If he did get
good data then by virtue of his different location, we
should be able to calculate accurate PA and separation
figures.

Thew, I did get carried away... :-)

So, the main reason I uploaded the video was to show
folks the secondary of Antares as 95% of the astro
community have never seen it before and also to show
the "power" of the occultation in splitting double
stars. I'm sorry I didn't explain things better in
the first place.

And finally, Geoff you are right, the reappearance of
the primary takes 5 or 6 frames for the star to reach
full intensity. How much is due to the star's
diameter and how much is "fresnel diffraction" is a
quandry beyone me. isn't this fun!

I'll run Limovie and get a nice graph to look at.

Regards
Dave

> "Tony George" wrote:
> > When I look at the video, I see first no star and
> a 'caret' symbol

> 7 seconds is too long for "fresnel diffraction" of
> even a biggy star like Antares isn't it?
>
> Thankyou for such an interesting puzzle Dave ;-)
> Regards, Geoff




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