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[Paulie pchris00]

Lunar observers! Want a way to tie your lunar observing to the upcoming transit of Venus? Try observing these craters named for astronomers associated with planetary transits. These are listed in the order of importance (according to me) of transit science, not the dates that they are observable before June 5.

We’ll start with the rayed crater Keplar. Nicolas Copernicus gets all the credit for introducing the Sun centered model of the solar system, but Johannes Kepler did the calculations to make that model work. Kepler correctly calculated the Mercury and Venus transits of 1631. To observe Kepler, point your telescope to the Moon the evening of May 31. (And why not observe Coperincus two days earlier, May 29?)




Virtual Moon Atlas




Kepler and Copernicus.


Next up is the large crater Gassendi (my favorite lunar feature). While Pierre Gassendi did not observe a Venus transit, he was the first known person to have observed a planetary transit of the Sun, the Mercury transit of 1631. To observe crater Gassendi near the lunar terminator before the Venus transit, try looking the evening of May 31.






Virtual Moon Atlas





Next we have the crater Horrocks. Young English astronomer Jeremiah Horrocks was the first person to observe a transit of Venus, in December 1639. What’s even more impressive is that he calculated that this transit would occur. The great mathematician Johannes Kepler had missed this transit in his calculations. Horrocks died just over a year after observing the transit, the day before he was supposed to meet with his friend William Crabtree, the only other person known to have observed the Venus transit of 1639. Horrocks was just 22 years old.

Crater Horrocks is located inside the crater Hipparchus, near the middle of the lunar disk. Try observing this pair the evening of May 27.




Virtual Moon Atlas.


While in the neighborhood of Hipparchus and Horrocks, let’s visit the crater Halley. Halley might be best known for the comet that now bears his name, but Halley observed a Mercury transit. After observing that transit, he realized that a Venus transit could be used to find the distance to Venus through parallax, and using Kepler’s laws, find the scale of the entire solar system. Halley then devised a method to find the parallax, and encouraged fellow astronomers to follow through with the necessary observations. Crater Halley is located just south of Hipparchus, so also observable the evening of May 27.




Virtual Moon Atlas.






Horrocks and Halley.


I'll have more soon. For now, I throw in these teases of DeLisle and Captain Cook.




De Lisle.




Cook (mirror reversed).

[Chicago Astronomer - Astro Joe]

This was fun and I appreciate the time it took to organize this.

Thanks Paulie...

[Paulie pchris00]

There is more coming.

[magic612]

Nicely done, Paulie!

[Paulie pchris00]

For the 1761 transit of Venus, possibly nobody’s story is more well known than French astronomer Jean-Baptiste Le Gentil (these French astronomers had more names than the Manhattan phone book. Google his full name if you dare). Le Gentil set sail for Pondicherry, India, but by the time he arrived, the city had fallen to British forces. Unable to land due to the hostile army, Le Gentil was forced to observe that transit aboard ship, where he could not determine his exact position, rendering the data useless.

Waiting out the next eight years in Madagascar, the Philippines, and at sea, Le Gentil returned to Pondicherry for the 1769 transit. This time he was able to set up an observatory. After a run of clear days the week before the transit, poor Le Gentil was clouded out for the entire transit. He’d spent more than 11 years away from home, with nothing to show for his dedication. And when he finally made it back to France, his relatives were trying to have him declared dead so they could "inherit" what they hadn't already stolen from Le Gentil's estate. And his job had been given to somebody else. Guy just couldn't catch a break.

Unfortunately, Le Gentil doesn’t fare much better on the Moon. His crater is located far to the south, in the zone of libration, and won’t be visible in the evening before our last transit of Venus.




Virtual Moon Atlas


This was a tough one. Being very near, or even partially on the southeastern limb, I'm not 100% certain I have this right. As far as I can tell, though, I was able to observe crater Le Gentil early this morning.











More coming soon. This has been a fun little diversion. I just wish I had more time to put into it.

[magic612]

Paulie, you should make some videos about this. Seriously. This is great stuff.

[Paulie pchris00]

Thanks. Lunar videos have been in the back of my mind for about two years now. It's something maybe I'll get around to eventually, or at least once in awhile. I'm taking a vacation the week of the transit, and with the Moon past full that week, it will give me plenty of time to do some observing in the wee hours of the night. No promises, but I'll try to do a lunar vid a few days after the transit.

If I do start making videos, they will be a review of an observation, like I've been doing on my lunar thread (got a LOT that I can post there), at least to start with. After I get a body of work- and some confidence- maybe I will try previews "Eyes on the Sky" style.

[Paulie pchris00]

Time to wrap up this thread before the new Moon, when our satellite returns to the evening sky for the last two weeks before the transit of Venus.

Nevil Maskelyne led an English expedition to the island of St. Helena- the same island Halley observed the 1677 transit of Mercury- for the 1761 transit of Venus. Unfortunately, Maskelyne was clouded out for the transit. His crater can be found in the south of Mare Tranquillitatis, and will be observable the evening of May 26.




Crater Maskelyne.


Scottish astronomer and optician James Short had the privilege of observing the 1761 Venus transit with members of the British royal family in London. His bigger contribution, though, came from calculating the Astronomical Unit based on the data from 1761 British expeditions. Short came up with an AU equal to 152.1 million kilometers, very much in the range of today’s AU of 149.6 million Km.








Crater Short.


Another British expedition for the 1761 transit was led by Charles Mason, along with his assistant Jeremiah Dixon. (They later surveyed the Pennsylvania/Maryland border. Ring a bell?) Originally slated to observe from Indonesia, their Royal Navy ship came under attack shortly after setting sail. With several of the crew killed, Mason returned to England, and for a time refused to set sail once again. Threatened with punitive action, Mason headed to Cape Town, South Africa. Clouded out for ingress, the pair were able to time the third contact. They stayed in Cape Town for months after to establish longitude.

Mason’s crater lies between Lacus Mortis and Lacus Somniorum (Lake of Death and Lake of Dreams; weird juxtaposition, huh)? It’s has been flooded from below, leaving only shallow walls. Observe Mason very near the terminator the evening of May 25, or wait a day until the 26th.










Crater Mason.


French astronomer Abbe Jean-Baptiste Chappe d’Auteroche (another Frenchman with too many names) traveled for both Venus transits of the eighteenth century. Chappe first traveled to Siberia. Clouds clearing just in time, Chappe was able to time both internal contacts. In 1769, Chappe’s expedition, along with a Spanish team, went to Baja California, Mexico. Again Chappe successfully timed both internal contact points. However, days later, most of his team fell ill to an epidemic that had plagued the locals when they arrived. Chappe also fell ill, but managed to observe a lunar eclipse just two weeks after the transit. Chappe died of his illness weeks later.

Like his countryman Le Gentil, Chappe’s crater lies in the zone of libration, along the visual eastern lunar limb. Virtual Moon Atlas shows Chappe visible late on the night of June 6, though it will be in full daylight, and very difficult to observe. I have never knowingly observed or imaged Chappe.


Our last story for this thread is perhaps the best known Transit of Venus story, the expedition of Captain James Cook to Tahiti. Cook’s team successfully observed the transit, although with the black drop effect, then unknown, Cook considered the observation a failure. Cook and crew then went on a voyage of discovery and through the South Seas. Commanding Endeavour and using new instrumentation, Cook was the first captain to know his position throughout his journey.

To find Cook’s lunar crater, look the evening of May 24. It lies at the southern end of Mare Fecunditatis, opposite and slightly north of Petavius.



Crater Cook, to the upper right of Petavious in this mirror reversed image.


Again, the 19th century transits of Venus were widely observed, and many expeditions mounted. This time the United States played a major role. Improved transportation had taken some of the risk out of these expeditions. Perhaps because of this, there aren’t the exciting stories surrounding the 1874 and 1882 transits, as compared with the 1760’s. Although the methods and instrumentation of observing had also much improved, there wasn’t the sense of discovery that there was during the previous pair of transits. And finally, other methods were giving better results for finding the scale of the solar system. Possibly for these reasons, I’m having a hard time finding lunar craters named for 19th century transit observers. While these astronomers and their observations are worth reading about, their stories aren’t found on the Moon with small telescopes. I’m disappointed by this, since I like to identify the features I see on the lunar surface, and find out a little bit of the people they’re named after.

Clear skies to all for the last Venus transit of our lifetimes, and please take a break from your transit preparation to enjoy a few moments checking out the features on our Moon.

[magic612]

Paulie, if you and Joe don't mind, I'm going to mention your thread here at Joe's site in my next video about the Venus transit. You've done a lot of great work here for people to be able to find and see these craters, and I'd like to direct them here if they are interested in seeing them.

[Chicago Astronomer - Astro Joe]

Dave,

Do it.

Mention that it was all done sober.

[Paulie pchris00]

I have no objection.

And unfortunately, Joe is correct.

Just don't ask if I was wearing pants while writing this...

[Paulie pchris00]

The transit might be over, but my lunar observing continues. I found another crater named for somebody I consider important to 18th century ToV observations. Pehr Wilhelm Wargentin was a Swedish astronomer, and as director of the Stockholm observatory, was influential in both observing and organizing expeditions throughout Scandinavia for the 1761 and 1769 transits.

Wargentin's crater is found just south of the large crater Schickard, which is in the visual southeast of the lunar surface.





I'm working on some new (and not so new) observations to post to my "I <3 Lunar Observing" thread, but this is all I have time for right now.

astronomer.proboards.com/index.cgi?board=Lunar&action=display&thread=3521

[Paulie pchris00]

If it's clear tomorrow, several of these craters should be favorable for observing, including le Gentil, Chappe, Wargentin, Pingre, and to a lesser degree, Short. Check them out if you can.

Upon further review, Chappe probably won't be visible until Wednesday night.

[Paulie pchris00]

Finally have a good libration for observing Le Gentil and Chappe and I'm clouded out...