Summer Solstice Observation

If I was independently wealthy, I could spend my days observing the motion of the Sun through the sky every clear day. Then, using a gnomon and marking the Sun’s shadow throughout the days and weeks of the year, I would have known the summer solstice was yesterday at 12:16 PM CDST. Since I don’t have the time to devote to those observations, I have to trust that every astronomical source listed that time as the point when the Sun shined directly over the Tropic of Cancer.

With a partly sunny day, I decided I would observe the Sun as it reached the solstice. The main point of the observation was to see how high the Sun appeared, both at the moment of solstice, and local high noon. Fortunately, here in Northwest Indiana, those two times were close together.

This was supposed to be a picture of date and time on my computer desktop gadgets, but all I got was my own reflection due to the strong sunlight.

The telescope was pointed very high, looking at the Sun just after the solstice, but before local high noon.

One large sunspot was near the center of the solar disk.

Looking high at the Sun.

Using one of the tripod legs of the solar telescope as a gnomon, I found that the Sun transited my central meridian at 12:48 PM CDST, only 32 minutes past the solstice. I wonder how rare it is for the summer solstice to fall so close to local high noon?

I used the front leg of the tripod as a gnomon. The crack in the patio runs north-south. The shadow is not yet covering the crack.

Approaching high noon.

Clouds rolling in threatened to ruin my high noon observation. Shadows faded, but didn't disappear.

The Sun reached the central meridian, it's highest point, at 12:48 CDST, thirty-two minutes after solstice.

The Sun was now past the meridian, and I ended the observation.

Today’s sunset will be a little earlier than yesterday, and a little further south, until we reach the winter solstice in December. As an astronomer, I welcome the longer nights, and will appreciate that the summer Sun won’t be quite as high when I’m observing sunspots (or other solar features).

The 2012 Venus Transit

For those who are unaware, roughly twice each century, Venus passes directly between the Sun and Earth, and are called transits. In 1677, after observing a transit of Mercury across the face of the Sun, Edmund Halley concluded that future transits could be used to determine solar parallax, and thus the distance to the sun, but that the rare Venus transits would be more useful. Halley then devised a system in which observers at multiple locations of widely separated latitudes would merely need to precisely time the transit from the moment the planet appears entirely on the disk of the sun until the moment the planet appears to make contact with the limb of the sun upon exiting. Obviously, this required that observation posts be located in zones where the entire transit was visible.                                                               

Jean-Nicolas Delisle, overseeing French preparations for the 1761 Transit of Venus, recognized that cloud cover at either point of contact would negate the entire operation. Instead, Delisle posited that parallax could be determined by timing either the beginning of transit (ingress), or the end (egress), and would reduce the chance of the interference of weather. Observing just one stage of transit, however, meant that it must be recorded in universal time, which would require knowing the exact longitude of the observation sites.                     

With precise timings, both the Halleyan and Delislean methods could be used to determine solar parallax. However, in 1761 precise timings proved to be difficult because of unanticipated visual phenomena. The first was that as Venus neared the limb of the sun, a bright ring seemed to encircle the planet. At the time, it was not known that Venus had an atmosphere, and that the ring was caused by refraction of sunlight as it passed through the Venusian atmosphere. Another unexpected problem was that the dark shape of Venus appeared to blur, as if it were a black drop, as it passed near the edge of the sun, the critical part of the observation. While observations of the 1761 Venus transit produced a range of solar parallax, the difficulties of dealing with these optical effects did not produce a consistent value. Taken by surprise, astronomers immediately began thinking about ways to reduce the effects for observations of the 1769 transit.                        

                   

When the 1769 transit failed to considerably improve upon the values of the previous observations, astronomers would have to wait more than 105 years to try again. A new generation, with a century’s worth of technological advances, anticipated the December 1874 Venus transit. With the invention of photography, French astronomer Herve Faye hoped that by capturing the defining moments on plates, the margin of error could be reduced, or possibly eliminated. Still, the same problems persisted, and though the transit was widely observed, reducing the observations to usable data also continued to be a long, tedious process.

In 1882, many nations once again sponsored parties to observe the Venus transit, despite evidence that other methods were returning better results for determining the scale of the solar system. This was partly because the various transit commissions were still in place from 1874, and also because after 1882 there would likely be no other chance to prove either the Halleyan or Delislean methods. While the nineteenth century transits of Venus helped to narrow the range of the AU, they were never as accurate as Halley had once hoped.

After 1882, Venus did not cross in front of the solar disk until 2004. I woke up very early June 8, 2004, and drove to the Adler planetarium, on Chicago’s lakefront museum campus. At sunrise, Venus would again be passing directly between Earth and the Sun. My memory of the details of is fuzzy (like my eyesight), but I saw the shape of Venus in front of the disk of the sun that morning. I had known that transits of Venus were rare events, and that many astronomers had traveled great distances to observe transits, but I did not know at the time why they were important to astronomers.           

I’d always had an interest in space and astronomy as a kid, but as a teenager and young adult, I lost most of my love for the starry night. During the 2004 transit, I had seen people along the Chicago lakefront observing with telescopes, but it never occurred to me to ask one of them if I could see for myself. I find it ironic now that my friend Chicago Astronomer Joe Guzman was at Adler, sharing the view with friends and the public. My transit observation, however, was limited to the cheap “eclipse glasses” sold at Adler for a few dollars. That look at Venus in front of the Sun was one of the reasons I came back to astronomy a few years ago. I wanted to see Venus in front of the Sun again, and knew that there would be only one more chance.

I have been waiting for next Venus transit for over seven years now. The transit of June 5-6, 2012 is less than a year away, and I have been spent much time thinking about how I will observe it. I’m formulating a plan, and although I only have modest equipment, I think I can gather data that can be used for the Delislean method of determining solar parallax. I would also like to share this event with the public, but my science observations will be my first priority. I have also been thinking about ways to reduce the possibility of being clouded by traveling on transit day. I will post my observation method soon, so that readers can start planning their own observations. Chicago Astronomer Curt Renz has created a graphic of the transit for observers at Adler Planetarium, and can be found at his website.

Start making your transit plans now, because this is our last chance to see this rare event, and I wish everybody clear skies on transit day!

Much of the information in this post I learned in the book "The Transits of Venus" by William Sheehan and John Westfall. I highly recommend reading it if you’re interested in viewing next year’s transit.


For information about Chicago area Transit of Venus plans, check this Chicago Astronomer forum.


To see a transit diagram for a city near you, check out Curt Renz's Venus Transit page.






http://www.sunaeon.com/venustransit/



For great overall transit information, check out the websites below.


Transit of Venus.org


http://transitofvenus.nl/wp/


And lastly, the authors of the websites above are frequent contributors in the Facebook group Transit of Venus.

Girl Scout Outing at Conway Observatory

On May 21, Calumet Astronomical Society hosted a group of Girl Scouts and their families at Conway Observatory in Lowell. I got to the observatory about 5:45, 15 minutes before the cookout was supposed to start. CAS members Maureen and Kim were our liaisons for the Girl Scouts. They are both deeply involved with them, and Maureen is a Girl Scout representative to NASA.

The forecast called for scattered storms throughout the afternoon and evening, but from 4 PM on, the general trend was a clearing sky. There was concern that we might not be able to observe after dark, but we were glad to have dodged the afternoon storms, and nothing looked to be approaching. When I arrived at Conway, Chris, Mike, Larry, Maureen, and Kim were getting ready for the visitors. Mike was setting up the grill for the cookout. The solar scope was set up, and the roof was open in the Hunter Astrophoto Lab. I’d seen the night before that the telescope and cameras were installed. The Girl Scouts (and families) hadn’t started arriving yet, so I opened my car, and staked out my piece of the concrete observing circle.

 

I put my scopes out, but left the dust caps on. Chris was working the solar telescope, and asked me if I wanted to view the Sun. Of course I did! I had borrowed the society’s Coronado personal solar telescope without realizing it rides piggyback on a 6” refractor with a white light filter. He pointed out that there was a prominence off the limb, and also I noticed a filament near the opposite limb.

The Sun with a white light filter...

...and with the Coronado hydrogen alpha filter.

When the visiting families started showing up, Chris asked if I wanted to operate the solar scope for the guests. I jumped at the chance. He showed me how to work the right ascension and declination controls, and I was off. I also used my solar set up, explaining how Galileo first observed sunspots.

CAS members with their telescopes and binoculars set up around the observing pad.

By 6:30 Mike had hamburgers and hot dogs off the grill. Waiting for the kids and visitors to eat, I sat and talked with Jim and Larry.

Mike cooking on the grill.

After getting a plate of food for myself, I wandered around the observatory and grounds, talking solar astronomy and explaining how the 16” telescope works with families who asked questions.

When the cookout was over, Maureen and Kim had activities planned for the girls, so I had time to get my telescopes ready. I walked over to the Hunter Astrophoto Lab to check out the new telescope. The telescope will be controlled by a netbook computer, or even remotely through a laptop with the proper software installed. The computer had not been installed yet, so I was a little surprised when the telescope started slewing while I was looking at it. I hadn’t touched anything, so I had a feeling Chris was messing with my head. I looked over to the observing pad and saw Chris with his laptop looking back at me. He was testing the system, and I heard later even tried imaging Saturn before dark.

Kim goes over a crater making experiment with a group.

Girls dropping rocks into different powders, creating craters and ejecta.

Of course I showed off the 16" LX200 to visitors checking it out.

My first real look at the Hunter telescope. Little did I know Chris was controlling it with his laptop from below.

With no Moon, everybody was getting anxious waiting for the first stars (and Saturn) to appear after sunset. Finally Arcturus and Saturn shined through the twilight, and there was a buzz around every telescope. There was too much twilight for deep sky objects, so Saturn and double stars such as Alcor/Mizar, and the Double Double in Lyra were the prime targets. The crowd was already thinning out before full darkness set, and even the Calumet astronomers were packing up by 10:30 PM. We did see a few meteors and a bright, high Iridium flare, the Beehive open star cluster, and globular star cluster M5. I tried the galaxies M65 & 66, and M104 to little fanfare.

It seemed like forever before the Sun dropped out of sight and twilight faded so we could observe the night sky!

It was a fun time, even though conditions were not the best. We knew we were lucky to see anything at all given the evening’s forecast. As the last CAS members were getting ready to leave, I knew I was going to stay out until the clouds came in, however late that might be, and I would have the observatory to myself. Just a few hours before I had never seen so many people and telescopes on the grounds, but now I was going to be able to explore the universe alone. Either way is fine with me.