In scanning through the Astronomy section of the
"Timetables of Science"
by Alexander Hellemans and Bryan Bunch
published by Touchstone Books
I came across the following
1737 John Bevis, at Greenwich Observatory, observes the passage of Venus in front of Mercury.
Let's look at the 1737 Venus-Mercury Occultation in detail. The path of these planets through the sky is shown below,
and as you can see the paths are at quite an angle with respect to each other.
A mutual planetary occulatation is so rare because of the small probability of one distance planet's disk will cover another. The orbits of the planets are tilted with respect to each other as well as the Earth's and the chance of all three aligning exactly is small. Below is the positions of Venus, Mercury and the Earth on May 28, 1737. Note that both Venus is closer moving to inferior conjuction while Mercury is on the far side of the Sun.
In order to see what the event look like, I generated the configuration using the planetarium program GUIDE version 7.0 (Project Pluto). Then by using the programs steps in time, I created a sequence of images over a 16 minute period for an animation. In this animation, the speed of Mercury has been increased by 100 times (each step is 1 minute but lasts only 0.3 seconds in the animation. The animation lasts 5 seconds and runs five times.
21:42 GMT, 7 minutes before mid-occultation
Click on image to see animation......
Field of View 2.8' x 2.0' arc
Location: Greenwich, England at 0o W, 51.5o N
Time of Mid-occultation: 21:49 GMT(9:49 pm) May 28, 1737 (Gregorian Calendar)
Some of the details are:
The planets are so low on the western horizon at the time of occulation that Bevis must have had trouble observing the event from Greenwich. Observers farther west would have had a better view but we have no records of any other observers of this event .
What did John Bevis see on May 28, 1737?
Bevis was an amateur but had access to the Greenwich Observatory. He used one of the 24 foot focal length telescopes. His
observations were in the evening just at the end of astronomical twilight.
Even in this one observation of such a rare event, Bevis was not able to see Mercury move behind Venus or emerge from the occultation.
Observers farther south would not have seen Mercury disappear behind Jupiter because of the parallax.