by Jane Houston Jones and Morris Jones
The Hunter moon rose on Thursday night. I love the moon and take every chance I get to see it. To share this vision with others is the best way to spend a bright night.
I was not able to observe the full moon in my usual telescopic manner this month, not that I'm complaining. I didn't have my telescope out. I was busy.
It is the time of the year where we assist John Dobson while he teaches his telescope making classes in San Francisco. It's a once-a-year time that I look forward to and cherish. The only mooning we did on Thursday night was through our eyes. We arrived with John at the Randall Museum in San Francisco for our telescope class. The moon was low and orangey in the San Francisco autumn city haze. The view of the city from the Randall Museum, nestled high atop upward jutting Buena Vista Hill was just spectacular. I don't know if I can describe it. I'll try, though.
San Francisco is a city of hills, and these hills represent some pretty interesting rock formations. In the daytime, there is fascinating geology here near the Randall Museum. Ribbon chert, which used to be the ocean bottom, smashed into the continent here. The rock pressed and crumpled into wavy ribbons of brittle rock, hence the name, ribbon chert. Sliding rocks on either side of the fault rubbed past each other and smoothed the rocks slick. Slickensides are what geologists call this phenomenon.
The shiny Franciscan ribbon chert slickensides can be seen just a block from where we polish our telescope mirrors.
I was amazed to read this conversation recently: It comes from Apollo 15.
[Slickensides are grooved or smoothed surfaces usually formed by friction, as on the two sides of a fault plane.]
[Fendell raises his aim and, past the 16-mm camera lens, we can see the lower slopes of Mt. Hadley at maximum zoom. He then pans to the right but, because of the reflected light reaching the lens, little detail is visible.]
And now, back to earth...It was time for class to begin.
Below our hilltop museum site the moon was the bright. The busy hooked angle of Market and Castro Streets looked like moving fireflies moving in formation. At the end of the bright lights of Market Street were two images. The glimmering San Francisco bay and the nearly full moon.
It was really beautiful so we brought the class out to look at the moon and the view. John launched into one of his his typical and classic questioning sessions.
"Why does the moon look so big"?, he asked.
He then told his illuminating and personal spin on the Moon Illusion effect. I really liked having this explained in plain English for a change. I think the students will remember the words and the view and be able to connect them and retell the story to others. That is what is important. Sharing the information is what is important.
Our genetic programming tells us that the sky is flat and nearby. You've seen birds fly overhead, and clouds pass, and you know that they are closest when they are directly overhead. Things on the horizon are more distant.
That unconscious part of the brain that assigns size to things decides that the moon must be very large when it is on the horizon because it's "so far away." The same moon overhead must be smaller because it's nearby. (Of course when we think about the appearance with our conscious brain, we think it must be closer on the horizon because it's larger. Brains just didn't evolve to deal with objects so large and so distant!)
Back in the classroom, we talked about building the rocker boxes for our telescopes. We can't just ignore the Universe here in the classroom, so the topic inevitably turns to Astronomy. John asked the students why the moon was so bright tonight.
When no one answered, he told about the glass beads being lit on the moon. Thankfully, my huband Mojo, elaborated on this point, for the students didn't know exactly why to ask or how to ask the question "what the heck are these glass beads, and what are they doing on the moon".
I found it fascinating to read the Apollo 15 journal, and to read about the astronauts who saw glass in the bottom of a small crater and slickensides mentioned in the same scoop of moon samples. It evokes an emotion when I view the moon. A few people not too different from me walked on the moon, observed the geology, and took some samples home with them. I like that thought alot!
The drive home from class gave us a different moon view. The moon over the Golden Gate Bridge was higher now and the orange hue had changed to a bright golden pearly Hunter Moon. It was two hours before full, but it was enough of a mooning night for us!
References:
SF Slickenside photo
http://www.geoscapesphotography.com/ca-slickensides.htm
Slickenside closeup
http://www.idcomm.com/personal/mtbrem/javatutorial/uinta/slicks.htm
A geology lesson
http://duke.usask.ca/~reeves/prog/geoe118/geoe118.052.html
Apollo 15 Lunar Journal
http://www.hq.nasa.gov/office/pao/History/alsj/a15/a15.sta6abv.html