Exoplanet XO-1b in CrB

Thanks bud!

Anthony.

Revisiting original posting and observation made by Dave MCDona re early transit time - I have the following question:

When transit predictions are calculated I assume that these take into considerations that the Earth in its orbit probably presents a different light path distance from the target. While I'm sure that this must be so I thought I'd raise the question.

Also, Anthony, on measuring long transits that involve multiple sessions at some significant time apart it may be necesary to factor this effect in (and I'm not sure how I would attack that problem).

The difference could be anything upto a little more than one Earth orbit radius light travel time - or about 8 mins.


Mark

Hi Michael,

I am not really convinced it matters nor does it affect anything. For example, with a lunar eclipse we have half the world able to observe it since they are in darkness. Such a transit would be the same thing, for it does not matter where you are located for the half of the world which is in darkness since the transit starts at a particular time and is technically available for those in darkness.

Anthony.

Have a look at the first measurement of the speed of light using IO / Jupiter eclipse timings by Ole Romer in 1676. I suggest that the distance of Earth from observed Jovian eclipse and planetary transit was/is very important - but only if observations are made over long enough times for Earth to move significantly in distance with respect to observed phenomenon - that doesn't happen with Earth / Lunar events.

en.wikipedia.org/wiki/Olaf_Roemer

Mark
PS - Cassini should have worked it out first...

Michael,

I suspect you are referring to the effect of parallax. However, the distance of these stars is so great that the parallax angle of the transiting exoplanet for different observers on the dark side of earth during a transit would be virtually zero.

Anthony.

Great to engage by the way Anthony. No, not parallax - changing radial distance affects timing - hence my reference to Jovian moon calculations leading to early estimate of speed of light.

Consider a clock to represent the Earths orbit. Centre of clock is the Sun. Earth is at 12 O'Clock. We have some distant periodic event some distance away in the direction of the twelve O'Clock direction. If we messure the timinng between two close events when the Earth is at the 12 O'Clock position it would be t seconds. By the time the Earth reaches three O'Clock position it is one earh orbit radius further away from source of signal(slightly more). Timing of the start of the same periodic events are skewed compared to original timings because it takes about an extra 8 minutes for the signal of the occurrence of those events to reach us - compared to the earlier timings.

It really only affects forward predictions of when things should happen or if periodic event isn't so close and time between start and end of event coincides with Earth moving significant course of its orbit.

Keep up the good work Anthony - I look forward to all your posts.


Mark (Not Michael - by the way)