[quote="Sandstone"][quote="Some dude"]
I've been watching Jupiter & Venus for some months now, and have a question...
If the two planets are on the same orbital plane, why is a conjunction not a single point in the sky?[/quote]
The planets' orbits are close to being in the same plane, but not exactly.
Using earth's orbit to define the plane (ecliptic), Venus's orbit tilts at 3.39 degrees to that plane,
and Jupiter's orbit tilts at 1.31 degrees to that plane.[/quote]
[quote=" http://en.wikipedia.org/wiki/Astronomical_transit"]
<<In rare cases, one planet can transit in front of another. The next time this will happen (as seen from Earth) will be on 22 November 2065 at about 12:43 UTC, when Venus near superior conjunction (with an angular diameter of 10.6") will transit in front of Jupiter (with an angular diameter of 30.9"); however, this will take place only 8° west of the Sun, and will therefore not be visible to the unaided/unprotected eye. 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. Before transiting Jupiter, Venus will occult Jupiter's moon Ganymede at around 11:24 UTC as seen from some southernmost parts of Earth. Parallax will cause actual observed times to vary by a few minutes, depending on the precise location of the observer.
[float=right][img3="[b][color=#0000FF]Simulation of Venus transiting Jupiter, as it did (unobserved) on 3 Jan. 1818.[/color][/b]"]http://upload.wikimedia.org/wikipedia/commons/3/3f/VtransitsJ.jpg[/img3][/float]There are only 18 mutual planetary transits and occultations as seen from Earth between 1700 and 2200. Note the long break of events between 1818 and 2065.
[list][b][color=#0000FF] 19 Sep 1702 – Jupiter occults Neptune
20 Jul 1705 – Mercury transits Jupiter
14 Jul 1708 – Mercury occults Uranus
4 Oct 1708 – Mercury transits Jupiter
28 May 1737 – Venus occults Mercury
29 Aug 1771 – Venus transits Saturn
21 Jul 1793 – Mercury occults Uranus
9 Dec 1808 – Mercury transits Saturn
3 Jan 1818 – Venus transits Jupiter
....................................................
22 Nov 2065 – Venus transits Jupiter
15 Jul 2067 – Mercury occults Neptune
11 Aug 2079 – Mercury occults Mars
27 Oct 2088 – Mercury transits Jupiter
7 Apr 2094 – Mercury transits Jupiter
21 Aug 2104 – Venus occults Neptune
14 Sep 2123 – Venus transits Jupiter
29 Jul 2126 – Mercury occults Mars
3 Dec 2133 – Venus occults Mercury[/color][/b][/list]
[b][color=#FF0000]The 1737 event was observed by John Bevis at Greenwich Observatory – [u]it is the only detailed account of a mutual planetary occultation[/u]. A transit of Mars across Jupiter on 12 Sep 1170 was observed by the monk Gervase at Canterbury, and by Chinese astronomers. In addition, an occultation of Mars by Venus was observed by Michael Maestlin at Heidelberg on 3 October 1590.[/color][/b]>>[/quote][quote=" http://transit.savage-garden.org/en/mutual.html"]
<<A total of 471 mutual planetary transit/occultation events occur in the time interval 5000 BC - 10000 AD. This makes an average frequency of one event in 32 years. However, these events are irregularly distributed in time. For instance, the shortest period of time between two consecutive mutual planetary events is a little over than 9 days. The transit of Venus in front of Saturn on 06 Mar 5199 is followed by a transit of Venus in front of Jupiter on 15 March 5199. [b][color=#FF0000]The longest period lacking of any mutual events is more than 90 538 days (almost 248 years) and [u]we are currently living in that gap[/u] between 03 Jan 1818 and 22 Nov 2065, on both occasions Venus is transiting Jupiter.[/color][/b]
For a planet to take part more frequently in mutual events two factors are decisive: fast apparent motion and large apparent diameter. The following table shows number of mutual events every planet takes part in:
The following table shows occurrence of mutual planetary events pairs (5000 BC - 10000 AD).
[code]Planets involved Events
-------------------------------
Venus Jupiter 86
Venus Saturn 55
Mercury Jupiter 43
Mercury Saturn 41
Mercury Venus 40
Venus Uranus 33
Mars Jupiter 25
Mercury Mars 25
Venus Neptune 25
Venus Mars 20
Mercury Neptune 18
Mercury Uranus 14
Mars Uranus 12
Mars Saturn 9
Jupiter Uranus 8
Mars Neptune 7
Jupiter Neptune 7
Jupiter Saturn 3
Saturn Uranus 0
Saturn Neptune 0
Uranus Neptune 0[/code][/quote]