Celestia Forums

Hello,
A trasit is due on June 5th-6th this year and Celestia is a great way to see it. I have used Celestia to recreate Captain Cook's south Sea measurements from Papeete. However, there is an aspect that puzzles me, in both transits there is a discrepancy in that the timings of Venus crossing the sun's limb and those published say here http://astro.ukho.gov.uk/nao/transit/V_2012/ , are different. For instance from London, UK, in Celestia there is no view of the transit at all whereas a part of it should be seen (Int Image).

The actual measurement in Celestia can be very precise - to the second - but it varies by as much as an hour or more against the published predictions.
This is, in my view, still very impressive.
Presumably the use of Spice Kernals for Venus and the Earth would be necessary to acheive more precision.

It may be that I'm not employing the correct technique in the way I set up Celestia.
Briefly Set date: Select Location say Papeete and Shift G to go to the location: Select Venus with 2: Track Venus with T: Use the comma key to get as close as neede to view the Venus's limb crossings.
Have I made a mistake?

David.

--- edit ---

David,

Using the standard Celestia 1.6.0 release, I find that the end of the transit IS VISIBLE from London and agrees within a few minutes of the times posted on the HM Nautical Almanac site per your link above. What may contribute to these differences is that Celestia 1) truncates VSOP87, 2) treats Earth as a perfect sphere, and 3) does not faithfully account for Light-Travel. All in all, that's still very impressive!

The following views are “London-centric” from:
Lat: 51.49999?; Lon”:-0.16668?; Altitude 11.111 meters

Interior Egress:
2012 Jun 6: Venus Transit (Interior Egress) 4:30:36 UTC Light Travel OFF
cel://SyncOrbit/Sol:Earth/2012-06-06T04:31:43.08574?x=7x6rrA6BGw&y=MaaBIduTIg&z=Zn6tuXsU&ow=-0.905677&ox=0.128383&oy=0.235504&oz=-0.328336&track=Sol:Venus&select=Sol:Venus&fov=0.0243539&ts=0.01&ltd=0&p=0&rf=-1407336945&lm=-1074937829&tsrc=0&ver=3

2012 Jun 6: Venus Transit (Interior Egress) 4:33:00 UTC Light Travel ON
cel://SyncOrbit/Sol:Earth/2012-06-06T04:31:42.69878?x=8B6rrA6BGw&y=M6aBIduTIg&z=ZX6tuXsU&ow=-0.905679&ox=0.128383&oy=0.235515&oz=-0.328323&track=Sol:Venus&select=Sol:Venus&fov=0.0243539&ts=-0.0001&ltd=1&p=0&rf=-1407336945&lm=-1074937829&tsrc=0&ver=3


Exterior Egress:
2012 Jun 6: Venus Transit (Exterior Egress) 4:48:11 UTC Light Travel OFF
cel://SyncOrbit/Sol:Earth/2012-06-06T04:49:18.07966?x=6R6rrA6BGw&y=LaaBIduTIg&z=ZH6tuXsU&ow=-0.909171&ox=0.137908&oy=0.202507&oz=-0.33672&track=Sol:Venus&select=Sol:Venus&fov=0.0243539&ts=0.01&ltd=0&p=0&rf=-1407336945&lm=-1074937829&tsrc=0&ver=3

2012 Jun 6: Venus Transit (Exterior Egress) 4:50:36 UTC Light Travel ON
cel://SyncOrbit/Sol:Earth/2012-06-06T04:49:18.64920?x=6h6rrA6BGw&y=L6aBIduTIg&z=Y36tuXsU&ow=-0.909169&ox=0.137911&oy=0.202491&oz=-0.336735&track=Sol:Venus&select=Sol:Venus&fov=0.0243539&ts=0.01&ltd=1&p=0&rf=-1407336945&lm=-1074937829&tsrc=0&ver=3

Enjoy!

-GW

An added link:
Sunrise in London, transit already underway and then proceeding to egress:
cel://SyncOrbit/Sol:Earth/2012-06-06T03:47:49.48083?x=5B6rrA6BGw&y=KqaBIduTIg&z=Yn6tuXsU&ow=-0.891133&ox=0.1085&oy=0.317515&oz=-0.305439&track=Sol:Venus&select=Sol:Venus&fov=0.816952&ts=100&ltd=1&p=0&rf=-1407336945&lm=-1074937829&tsrc=0&ver=3

One final link:
Geo-centric View. Literally from less than a thousandth of a meter from the center of Earth. Seems to also agree well (within a few minutes) with HM Nautical Almanac: (Celestial North is straight up.)
cel://PhaseLock/Sol:Earth/Sol/2012-06-05T20:29:20.31209?x=og4&y=bev//////////////////w&z=dhw&ow=0.525745&ox=-0.472855&oy=0.525745&oz=0.472855&select=Sol:Venus&fov=0.609622&ts=1000&ltd=1&p=0&rf=-1407336881&lm=-1074937829&tsrc=0&ver=3

Thanks John and GW for the in depth response which clearly shows that the transit is visible from London.

I'm most puzzled though.

My method of selecting London as the view point is:-
"London" with Enter/Name/Enter then Ctrl G to go to the surface at London. The coords are shown correctly although the height is shown as 500m.
Because this method fixes the height at 500m I surmise that your more elegant approach was to use the Goto Coord in the Navigation Menu.

cel://SyncOrbit/Sol:Earth:London/2012-06-05T20:10:12.87832?x=fFXq8sU&y=JBfYQhg&z=XHTzc2w&ow=0.118429&ox=-0.32009&oy=-0.939166&oz=-0.0385355&track=Sol:Venus&select=Sol:Earth:London&fov=2.3296&ts=1&ltd=0&p=1&rf=-1409180141&lm=-1074937710&tsrc=0&ver=3

The link shows the position just before the commencement of the Transit with Earth's horizon "coming up" from the bottom of the screen. As you will see the transit is completely obscured.

As I said in my first post I must have made a mistake but I'm not sure where. Any idea?

Regards, David.

David,

The problem is that you are looking at the start of the transit, which happens at 22:00 UT, which is after sunset on June 5th in London. Only the end of the transit is visible in London. That's 6 hours later, near 4:30 -- at about sunrise on the 6th.

[EDIT]
Here's a URL viewing the end of the transit from London at sunrise:

cel://SyncOrbit/Sol:Earth/2012-06-06T03 ... rc=0&ver=3

[/edit]

Many thanks Seleden.
What an idiot I am!!!!

Please forgive me for all the palaver, David.

David,

You're very welcome. I must admit it took me a while to realize what was causing the problem.