# Talk:1639 transit of Venus

I added a few lines at the beginning of the "Results" section. His observation didn't really allow him to determine the distance (AU=astronomical unit). (It takes careful measurements, including timing, at two places far removed from each other, as was done in later observation campaigns.) It seems Horrocks was mainly interested in measuring the apparent size of Venus (as was his colleague Crabtree). He then used an assumption which it seems was more or less shared by some other contemporaries, that the sizes (diameters) of the planets were proportional to their distance from the sun. This then would of course allows to determine the actual distance of Venus (expressed in earth radii) and thus the AU. Thus this was more of a lucky guess, as Venus is only some rough 30% larger than what would be expected from the assumed "law". For the moment I don't have a better reference than:
http://adsabs.harvard.edu/full/2005A%26G....46a..14H
Greetings,79.3.206.62 (talk) 17:05, 3 June 2012 (UTC)

Yes, that sounds about right. I knew about the false assumption he made about the size of the planets but I'm no astronomer or mathematician and I still haven't had time to get my head round the concept properly. Too busy trying to get this and the Transit of Venus article ready for the main page on the 5th of June. Richerman   (talk) 18:18, 3 June 2012 (UTC)
Thanks for clearing that up as I have been wondering about it. Someone needs to add the above link as a reference (I'll get around to it, but no time now, particularly since I'll have to examine the document first). Johnuniq (talk) 02:35, 4 June 2012 (UTC)
I've added the reference but this needs a bit more work. I tried to rewrite it but I'm not sure if I got it completely right. My proposed text is below:

Kepler had found that the distance between the planets increased in proportion to their distance from the Sun and his mystical mind led him to assume that the universe was created with a divine harmony and the size of the planets would increase in the same way. He had written in 1618 "Nothing is more in concord with nature than that the order of magnitude should be the the same as the order of the spheres". When Horrocks found that this was true of Venus and Mercury he tentatively proposed a law that said "All planets, (with the exception of Mars) are the same angular size, this being 28 arc seconds" This meant that the assumption his hero Kepler had made about the sizes of the planets held true and led to the erroneous conclusion that the distance between each planet and the Sun was about 15,000 times its radius. Thus he estimated the distance from the Earth to the Sun to be approximately 60 million miles (97 million km) – suggesting the solar system was ten times larger than traditionally believed.

From my reading of Aughton's book there was more evidence from his observations of the other planets that led him to propose the law but I've not digested it all yet. Does that summary look about right? Richerman   (talk) 10:58, 4 June 2012 (UTC)
I believe that's reasonable, although there should be an explanation that the 28 arcseconds is the angular diameter of a planet, as seen from the Sun. I think some rewording is needed as it may suggest that Horrocks observed Mercury, whereas he did calculations from Piere Gassendi's observations of the 1631 transit of Mercury, and used Kepler's (incorrect) values for the Mercury–Earth/Mercury–Sun distances; those calculations (according to the article) concluded that Mercury had an angular diameter of 28″ seen from the Sun. Also, some improvement on "hero" is needed. I have to go now, so can't do anything useful, but here is an extract from some notes I took a couple of hours ago, while reading the harvard.edu link above (I'm not proposing this for the article, but it is a summary of a signficant point that I think was made by the article, and "veneration" is more suitable than "hero"):Perhaps Horrocks thought his unfounded law was reasonable given a veneration of Kepler, and the mystery of Kepler's third law (for which they had no explanation). If the cube of the planet–Sun distance was proportional to the square of the period of the planet's orbit, why should there not be a proportionality between the planet–Sun distance and the planet radius? Johnuniq (talk) 11:26, 4 June 2012 (UTC)
Thanks John, I've changed the text now. Richerman   (talk) 01:16, 5 June 2012 (UTC)

This review is transcluded from Talk:Transit of Venus, 1639/GA1. The edit link for this section can be used to add comments to the review.
Reviewer: Adam Cuerden (talk · contribs) 19:01, 27 August 2013 (UTC)
I think the major issue this has on a quick skim is Episode 13:  Anonymous (24 November 2009). "An important anniversary in the history of science". The Renaissance Mathematics. wordpress.com. Retrieved 11 May 2012.
Can you state why this blog is acceptable under WP:RS? Adam Cuerden (talk) 19:01, 27 August 2013 (UTC)
Reply Er - it's not. I've no idea why I put that one in, I mustn't have realised it was a blog. I've replaced it. Richerman   (talk) 10:33, 28 August 2013 (UTC)
Right. I'm afraid this is going to be a fairly boring review beyond that point, then. This is an excellently-written, very competently-put-together article. Still, there are a few points.
General

Lots of missing commas. I've copyedited accordingly, also making other small adjustments, so this may be considered dealt with
Reply Hmm - I think some of those are a bit controversial - ,and, - that's at least one too many. Richerman   (talk) 19:33, 28 August 2013 (UTC)

I do try to cut down on my Victorianism when it comes to commas, but a few may slip by. Feel free to remove some, but I think that more than there were does make it more readable. . Adam Cuerden (talk) 21:24, 28 August 2013 (UTC)
However, do note that , and , is actually required in some cases. When the structure is something like [Independent clause], and, [comma-delineated phrase connected to IC2], [independent clause 2].  it's always necessary. For example. "Billy went to the market, and, while he was there, Sally saw him." Where I tend to exceed normal usage is that, when commas are optional in modern usage, I tend to default to putting them in. Still, I think the article did need more commas than it had.  Adam Cuerden (talk) 21:30, 28 August 2013 (UTC)
Background
"suggesting that observations of a Venus transit would be more useful scientifically." - This reads, in context, as saying that observations of the Venus transit would be more useful than observations of a Mercury transit. I suspect you mean that the observations of the Mercury transit proving scientifically valuable indicated that the Venus transit would also be valuable, which isn't the same thing.
Reply No, it means that Mercury was too small to be useful for techniques such as the parallax method but I'll check up on that and clarify it. Richerman   (talk) 19:33, 28 August 2013 (UTC)
William Crabtree

It would be good to provide a translation for "Nos Keplari".
Reply I would translate it as 'We Keplarians' but I've never found a reference for it anywhere. I'll put that in and see if anyone objects later. Richerman   (talk) 19:33, 28 August 2013 (UTC)
Transit of Mercury

"[...]around one minute of arc when seen as the bright morning star close to the Sun" - I'd suggest something like "[...]around one minute of arc in its normal position of the bright morning star close to the Sun." - I would've copyedited this, but was worried about exact phrasing.
Reply That sounds reasonable to me. Richerman   (talk) 19:33, 28 August 2013 (UTC)
I have a rule for promotion of these. If the problems are trivial and few, there's really no need to wait on them for promotion. This is an excellent article, and, whilst the... three points raised... should be fixed, I really don't think that's enough to block GA. Indeed, once they are fixed, I would consider this immediately ready to go to FAC.  Pass. Adam Cuerden (talk) 17:55, 28 August 2013 (UTC)
Comment Thanks for your review and the kind words. I was thinking of going to FAC with it but I'll need to standardise the citation style first. Then I'll have to make sure I have the time to deal with the flak :) Richerman   (talk) 19:33, 28 August 2013 (UTC)