Talk:Transit (astronomy)

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Image Venus/Jupiter[edit]

Venus transiting Jupiter.

A simulation of Venus transiting Jupiter, as it did on January 3, 1818. ? Err exactly what position of observation renders that view of Venus transiting Jupiter. This image should be removed, not only is it nonsensical and badly put together aswell.

Dear anonymous flamer: Had you bothered to check the information contained in that image file, the illustration was created using Starry Night Pro software. It is VERY possible (although VERY rare) for one planet to pass in front of another as viewed from earth. In the case of Venus and Jupiter, since Venus will always be the closer planet to Earth, it will always be seen transiting Jupiter rather than the converse. Bart 00:44, 12 July 2006 (UTC)

On 1818-Jan-03, Jupiter was 6.2AU and Venus 1.6AU from the Earth. Both were on the opposite side of the Sun in the constellation Sagittarius and 16 degress from the Sun in the morning sky. -- Kheider (talk) 17:40, 9 June 2008 (UTC)

Venus / Jupiter transition[edit]

Hi, What is the point of the Venus/Jupiter image and in what way is it a simulation? Unless Venus in 1818 suddenly jumped about 4.5 AUs then I can't see how it is a simulation of anything other than questionable photo shopping? Cheers Khukri 10:56, 1 July 2010 (UTC)

This concern has been discussed before. Jupiter and Venus frequently hang out near the Sun as seen in our sky. -- Kheider (talk) 11:20, 1 July 2010 (UTC)

Accuracy[edit]

How is this accurate? Is the relative sizes of the discs of Jupiter and Venus correct? What distance from Venus was the origin point for this simulation? -- 65.92.180.137 (talk) 23:40, 23 February 2013 (UTC)

Definitions[edit]

I have some issues with the article. Several "definitions" seem confusing. For instance, the definition itself says that the nearer object is apparently smaller in size than the more distant object. While strictly mathematically speaking this is correct, the natural understanding of perspective would suggest something along the line "The transitting object is closer to the observer than the more distant object, which, consequently, appears to be smaller than it actually is; for instance, Venus transitting Sun covers significant portion of Sun, while in reality, it is less than (exact value here) of Sun's diameter." Another problematic part is "When the nearer object has a larger angular diameter than the farther object, thus covering it completely" in "Mutual planetary..." -- The problem is that for a closer object to cover a distant object completely, the closer object need not be larger (Moon can cover Sun when observed from Earth during Solar "eclipses"). It worries me that the definitions in this article do not have citation marks at them. Thanks for your time. Alcator 195.146.147.26 (talk) 09:55, 2 January 2009 (UTC)

It looks fairly good to me. It might be more confusing to make the definition too wordy. We do not want to confuse a simple transit with a full occultation. The angular diameter of a smaller object can easily be larger than a physically larger object at a much greater distance. I suggest re-reading the angular diameter article. It explains and gives a range for the apparent sizes of well known bodies in the solar system as seen from the Earth. -- Kheider (talk) 16:51, 2 January 2009 (UTC)
Question regarding definitions: This idea occurs 3 times on the page: 1. If the first celestial body hides a major part, or all of, the second celestial body, then it is an occultation rather than a transit. 2. Cases where the nearer object appears larger and completely hides the more distant object are known as occultations. 3. When the nearer object has a larger angular diameter than the farther object, thus covering it completely, the event is not a transit but an occultation.
Would a "full occultation" not be an eclipse? AuthorizeditorA 23:51, 27 April 2012 (UTC) — Preceding unsigned comment added by AuthorizeditorA (talkcontribs)

Distance from Sun[edit]

This article does not mention that transits were used estimate the distance between the Earth and the Sun [1] and hence (via Kepler's laws) the scale of the solar system. MichaelSH 13:30, 8 November 2006 (UTC)

Important point. Is there any reason not to revise the article? Even the first version from 2003 has qualities which are now lacking.

--d-axel (talk) 00:40, 3 February 2009 (UTC)

Contact times[edit]

The article mentions first, second, third and fourth contact. It should also mention the case of partial transits, where there is no second and third contact. Is that still considered a transit? --B.d.mills 08:33, 5 March 2007 (UTC)

Transits of Earth from Ceres or Vesta[edit]

When I first heard of the Earth can pass between the Sun and Mars, I am curious as to how often it passes between the Sun and the largest asteroids - Ceres and 4 Vesta.

Transits of Earth from Ceres (I checked on a website showing asteroid orbits) can occur in June or December. Ceres is closer to aphelion at a June transit. Those from 4 Vesta occur in early January or early July, and I found that the Earth did pass between the Sun and 4 Vesta on 3 January 1937 and 3 July 1960.

Should I write an article Transit of Earth from Ceres or Transit of Earth from 4 Vesta??

Luokehao 00:18, 10 August 2007 (UTC)

Proper name?[edit]

"Astronomical transit" references overwhelmingly as another name for a Meridian circle[2]. This articles should probably be moved to "Transit (astronomical)". Fountains of Bryn Mawr (talk) 13:32, 4 February 2010 (UTC)

I propose as a new page name "Transit (astronomy)". Sae1962 (talk) 18:25, 28 December 2011 (UTC)
Good suggestion Drlectin (talk) 12:35, 17 January 2012 (UTC)
Yes, good suggestion. Is anyone planning to to do the move? Tfr000 (talk) 14:31, 3 May 2012 (UTC)

Uranus transits Neptune[edit]

Article says it will happen 01 Dec 40396. What is the source for this? There is no such transit on that date as far as Stellarium is concerned (which admittedly is not the most accurate source). The closest I can get them is around 10 June 40398, but they're still nowhere near a transit. Why is it so difficult to calculate these positions? Globe199 (talk) 17:08, 7 June 2012 (UTC)

Looking at Talk:Transit of Uranus from Neptune it looks like Solex 9.1 gave a year of 38172. -- Kheider (talk) 19:54, 7 June 2012 (UTC)
It is so difficult because we do not have complete information about the exact motions of everything in the solar system. Even if we had very exact descriptions of the motions of Uranus and Neptune, throwing a few small, not-very-well-observed asteroids into the mix would completely change any long-term predictions we tried to make. Long term in this case being more than a few centuries. So predictions 38000 years in the future are pretty rough, and anything like two planets passing across each other at that time is not really possible to predict one way or the other, with the current state of the art. Tfr000 (talk) 11:08, 15 August 2012 (UTC)
Correction. Predictions for the positions of the planets are easily reliable for thousands of years, if you are using a properly written program. It is only the positions of the asteroids that can not be predicted more than a few centuries. The planets are not so easily perturbed. -- Kheider (talk) 12:37, 15 August 2012 (UTC)
True, the planets are not easily perturbed in real time. Cumulatively, it's not that difficult for them to be moved around in the distant future, easily enough for them to miss an occultation. Here's some reading material [3] [4] We just do not have sufficient data to predict accurately 10,000 years out, other than, perhaps, to say two planets will pass close to each other, but we don't know how close. Tfr000 (talk) 11:14, 16 August 2012 (UTC)
My understanding is that planetary transits as seen from Earth are now accurate for up to ±80000 years when using a proper step-size. Your first reference is from 2001 and that is somewhat dated now. -- Kheider (talk) 11:32, 16 August 2012 (UTC)
It's possible. As far as I currently know, the inaccuracies in asteroid masses described in the articles are still relevant - unless there is a new method of estimating them more accurately that I am unaware of. I'm not in astronomy by profession, so I don't see the most current info as it appears. Tfr000 (talk) 11:19, 17 August 2012 (UTC)
The masses of the big 3 asteroids are better known now than they were 10 years ago. The asteroids perturb Mars more than any of the other planet. Mars has to get notably perturbed by the asteroids before Mars position errors can notably cause errors in the position of Earth. The 4 gas giants are going to be the last planets to worry about small solar system bodies, so a high-end simulation of Uranus+Neptune in 40000 years should be accurate. -- Kheider (talk) 14:29, 17 August 2012 (UTC)
Here's some more stuff to look at, for anyone following this. [5] [6] In the first paper, note the graphs giving differences in position and uncertainty between DE421 and DE423, for the period 1900 to 2050 (fig 11, 14, 15, 17). Solex version 10 was apparently based on DE421. Note how the position and uncertainty grow substantially over a period of one century for the planets investigated. The planets not involved in the new fits for DE423 almost certainly grow in error by much higher amounts. In fact the first paper mentions For Uranus and Neptune the assessment of older data sets is not as complete as for Pluto so relatively few data have been included. These orbits are reasonably accurate for the current times due to modern astrometry and knowledge from the Voyager encounters. The Uranus and Neptune data sets will be expanded in a future ephemeris. Tfr000 (talk) 11:18, 23 August 2012 (UTC)
I have been looking for information on where Vitagliano got the information that numerically integrated orbits are good for 80,000 years. JPL seldom claims accuracy beyond ±3000 years, and their longest ephemeris was for ±10,000 years, but it was unrealesed - probably special-purpose for some researcher's needs. At the bottom of this [7] Vitagliano compares positions of various bodies with and without asteroids to perturb them, giving us a worst case. Unfortunately, he does not give his results to better than 0°.01, which is larger than the expected error. At that level, their is little diffierence in the results, but errors that large could cause the outer planets, with their small disks, to miss each other! Vitagliano's Solex is derived from JPL's ephemerides, thus we can't expect it to be better in accuracy. Tfr000 (talk) 11:14, 24 August 2012 (UTC)
I have not yet read all of the above papers, but as I said earlier that asteroids will have a much larger affect on Mars because Mars is closest to them and Mars is the second least massive planet. Mars is kind of a wimp. For planets outside of both the asteroid belt and the Sun-Jupiter barycenter of the Solar System, perturbations will be much smaller. Uranus and Neptune will not be so easily perturbed as Mars and Venus. The only questions is how good are the known starting points for Uranus and Neptune given that neither planet has ever had an orbiter? Currently we simply do not know. -- Kheider (talk) 14:00, 24 August 2012 (UTC)

Oddly, the Wikilink to Timeline_of_the_far_future#Astronomical_events which is included in the brief description of the above event, does not contain any mention of such an event. Tfr000 (talk) 18:17, 16 May 2013 (UTC)

Meridian observation[edit]

Meridian observation was a a method of approximating a longitude. currently used on Wikipedia in articles concerned with original estimates of the location of the Pitcairn Islands. Edmund Roberts (diplomat) mentions it in conjunction with Lunar distance (navigation). --Pawyilee (talk) 13:55, 7 December 2012 (UTC)

Requested move[edit]

Astronomical transitTransit (astronomy) – As a result of earlier discussion at Talk:Astronomical transit#Proper name? there seems consensus. The target is presently a redirect to this article and moving requires admin action. Thincat (talk) 14:15, 23 February 2013 (UTC)