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From: TerryMoselaol.com
Date: Sun, 6 Jun 2004 13:44:21 EDT
Subject: Venus on SOHO, next transits

Hi all,

Venus is still very bright on the LASCO C3 images, even though the phase is 
only 0.001! I wonder will it remain bright even when the phase reduces to 
almost zero just before the transit, when it will disappear behind the instrument's 
occulting device? The brightness indicates that a certain amount of sunlight 
must be being 'forward scattered' through the upper Venusian atmosphere.

Incidentally, we will never be able to see Venus as close to the Sun as this, 
except via SOHO, during any of the Total Solar Eclipses from now until 2020 
inclusive. The nearest will be on 20 July, 2019, in the South Pacific, when 
Venus will be about 7 deg away during totality, but it will then be near Superior 
Conjunction, not Inferior Conjunction, and so will appear nearly 'Full', not 
as a slender crescent.

I'm glad to say that Dr David Asher at Armagh Observatory has confirmed that 
my SkyMap's calculation of the local circumstances of the 2117 transit showing 
that that transit will NOT be visible at all from Ireland are correct. See:

David wondered whether it would be the following one, on 8 Dec 2125, which 
would be partly visible from Ireland? The geocentric mid-time of that transit is 
16h 01m 46s, with a duration of 05h 50m.  So let's say a start time of 13h 
37m, and ending at 18h 27m.

The Sun sets from Belfast at 15.58 that day, just before mid-transit (unless 
the local mid-time is significantly later than the geocentric time: even so, 
in practice we won't see mid-transit!). But we'll see almost the first half of 
the event, weather permitting. But in SW Ireland sunset will be later, e.g. it 
will set at 16.29 at Schull, so observers there should see a little bit more 
than half of the whole event. Thus, for all observers in UK/Ireland, that 
Transit will be only partially visible. 

I'm grateful to Mario di Maggio for the following:  If astronauts were to 
stand on Mars in November 2084 they could catch a transit of Earth, and see their 
home planet cross the face of the Sun! (Don't forget your solar filter if 
you're going - it's a long way to have to come back to get it....!  T.M.)

But the important point is that THIS one, on Tuesday, is the only Venus 
Transit which will be completely visible from Ireland in any of our lifetimes, so 
DO make an effort to see it!

The forecast for Tuesday morning is now looking much more hopeful, so let's 
see you all at the IAA Transit Watch at Botanic Gardens from 08.30 to about 
12.20. Entrance via the Ulster Museum on Stranmillis Road; or if it suits you 
better, you can enter from Botanic Avenue.

Clear Skies to all,

Terry Moseley

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