Lunar Connection to the June 2012 Transit of Venus

I wanted to do this as a regular post, but it was going to take too much time to copy and paste everything together. Instead click the link in the title to see a post I wrote on Chicago Astronomer. Now that the Moon is back in the evening sky for the last two weeks before the Transit of Venus, the idea is to observe some lunar features named after people who have contributed to transit science.

I hope you have some fun with Luna while counting down these final days until the transit, and clear skies on either June 5 or 6, whichever day ToV falls on in your region.

Comparing Lunar Librations

With an unexpectedly clear sky last night, I found myself observing the Moon (well before the occultation of Zeta Tauri). I would have guessed the waxing gibbous Moon was about 8 days old at the time. I was caught up in observing and imaging what I could see, not what I might have expected to see.

Later that night, while looking through the images I'd taken, I realized that normally on an eight day old (it was actually nine days old, although I didn't know that yet) Moon, Rupes Recta- the Straight Wall- can be seen. I hadn't noticed it while observing, but I didn't specifically look for it. Later, while looking through my images, I saw that Rupes Recta was in full daylight, and therefore not visible. This led me to believe that libration had turned the visual western limb away from us.

I remembered that in early October 2011 I had noticed libration tilting the other direction, allowing me to see the "far side" along the visual western limb. I checked an image I took October 4 that is a similar lunar phase. Sure enough, the images from these two nights show a starkly different lunar landscape.

October 4, 2011- 7:50 PM CDST.

March 1, 2012- 8:12 PM CST.

Wanting to know more about these two nights, I looked up some information from the Virtual Moon Atlas:

October 4, 2011- 7:50 PM CDST

Distance- 383908km

Apparent Diameter- 31.13’

Lunation- 7.53 days

Illumination- 59.3%

Sub-solar latitude- -1.4°

Libration in latitude- -2° 57’

Libration in longitude- +7° 14’          

March 1, 2012- 8:13 PM CST

Distance- 391694km

Apparent Diameter- 30.51’

Lunation- 9.15 days

Illumination- 60%

Sub-solar latitude- +1.5°

Libration in latitude- +1° 53’

Libration in longitude- -6° 0’

Credit: Virtual Moon Atlas.

Although the phase looks very similar, VMA gives a difference in lunation of over 36 hours. The difference in illumination, though, is only 0.7%, close enough that even very skilled observers would notice little difference, in my opinion. The difference in libration in longitude, however, is over 13 degrees. Luna's visual western limb was indeed turned away from us last night.

For further comparison, I’ve found an image from October 5, and details from Virtual Moon Atlas.

October 5, 2011- 9:00 PM CDST

Distance- 388667km

Apparent Diameter- 30.74’

Lunation-  8.58 days

Illumination- 69.6%

Sub-solar latitude- -1.4°

Libration in latitude- 4° 09 ’

Libration in longitude- +6° 39’

Credit: Virtual Moon Atlas

While the lunation of 8.58 days on October 5 is still over half a day short of last night's 9.15 days, the Moon shows a much fuller disk, and was over 69% illuminated. It's a neat comparison, but I think October 4 better illustrates the difference in libration.

InOMN Valpo, Oct. 8, 2011

Astronomers were in high demand everywhere last Saturday, October 8th. I was asked to work at three different sites for International Observe the Moon Night, including with Chicago Astronomers, but had to turn them all down. I wanted to do a hometown session. Calumet Astronomical Society had a Girl Scout event in Country Club Hills, and in the west or near-northwest suburbs (I've forgotten exactly where). Indeed, people like us were in high demand all over the planet for InOMN 2011.

Since the date of InOMN 2011 was announced a few months ago, I'd planned to do a session at Valpo's new Central Park Plaza, sometimes referred to as Valpo's Millennium Park. The lighting in the area make it hostile for astronomy, but it's central location in the city makes for decent foot traffic. I spent four nights there from October 1st through the 6th, getting familiar with both the location and our Moon.

I invited my friends through Facebook, my atheist Meet-up group, and asked for any interested astronomers to join me on the private CASX boards, but otherwise didn't promote it. I had a few people interested, and Calumet Astronomical Society member Jeff offered to bring out an extra scope. Hillary came along as photographer and astronomer, giving us a total of three crew members, and four telescopes.

Hillary and I had pizza at Greek's Pizza, just on the other side of the park, then walked over at 6 PM to set up. Jeff arrived as we were hauling out our gear. I took my time setting up, walking around the park taking pictures of the park before sunset.

Hillary & Jeff.

Hillary with her 60mm shorty refractor.

Me with my 4.5" go-to Newtonian.

Jeff with his 8" LX90.

Already starting to attract attention.

I had to move my Dob for the early visitors while we waited for the Moon to clear the bank next to the park.

 

Jeff brought an 8” Meade LX90, Hillary her 60mm shorty refractor, and I had my 4.5” go-to and 6”Dobsonian. Hillary and I offered low powered lunar views all night, while Jeff opted for higher magnification, and a neutral density filter for more comfortable viewing. I had a small lunar map clipped to the side of my go-to Newt, and Jeff and I both sported 3 ft. wide laminated maps. I used mine often, as the large basin Shickard was placed right on the terminator. It’s western rim was illuminated, but the crater was in deep shadow, and drew a lot of attention. I also had to frequently explain the formation of maria, and that they are much younger than the heavily cratered highlands.

Hillary and Jeff stayed with the Moon all night, but once Jupiter appeared over the rooftops on Lincolnway, I positioned my Dob to show it as well. And to tie the Jovian experience to InOMN, I pointed out that those little points of light to either side of Jupiter, the wonderful and varied Galilean Moons, were roughly the same size as our Moon. Really, compared to the gas giant, they’re not much smaller than Earth. That help give a scale of distance, as well as pointing out that the light they’re seeing from the Jovian system took about 40 minutes to reach their eye.

I used my Dob, which was big enough to show the Jovian system well, yet easy to move, for views of Jupiter and the Galilean Moons.

The large crater Shickard, lying along the southern terminator, was frequently asked about.

Nobody counted, but the three of us easily attended to over one hundred visitors before calling it quits just before 10 PM. Between all the telescopes, red lights blinking everywhere, and me flashing my green laser around the park, we drew in a crowd larger than I think I could handle on my own. Thanks to Hillary and Jeff for helping out, and making it a fantastic night for all.

A parting crew shot. Many thanks to Jeff and Hillary for coming out, and making this a fun, informative event.

Read about the Chicago Astronomer InOMN event near Adler Planetarium.