Tuesday, July 24, 2012

Boiling Sun

Prelude to Disaster

More sunspots had rotated onto the Sun's disk just three days after my June 26 solar observations. Despite predicted scorching temperature I decided to try imaging the now multi-spotted Sun. My solar telescope and camera were hastily set up as early as possible on the morning of June 29, but I was immediately disappointed by poor seeing conditions. Solar features wavered so much it was hard to focus. I persevered hoping for some moments of atmospheric calm. It takes about 27 seconds to record enough video to produce one still image, so I needed just a few 27-second periods of relative calm. Only one hour after beginning I was pouring sweat and starting to feel woozy as the temperature reached 90F (32.2C). At that point some high clouds began crossing the Sun. It was time to quit.

Even though seeing was generally poor, I was able to capture four respectable images. First, look at sunspot 1515, a growing monster which later became very big, complex, and eruptive:
Sunspot 1515 (Click for full detail.)
Notice the big prominence arching upward on the left side of the image above. Here's an image showing just this prominence:
Sunspot 1513 had also rotated onto the Sun's disk since June 26:
Sunspot 1513 (Click for full detail.)
Finally, sunspot 1512, also present on June 26, still existed on June 29. Here it is accompanied by a filament:
Sunspot 1512 and filament (Click for full detail.)
The morning imaging session was a prelude to disaster! A few hours after packing up my gear afternoon temperatures at my observing site reached 107F (41.7C)! That evening extremely violent storms with maximum winds near 90 MPH (145 km/hr) passed through knocking out electric power over wide areas of Virginia and several other states. Tree limbs were down everywhere, but my home was not damaged. It took a couple hours to clean my yard the next morning. Unfortunately, our electric power was out for 2.7 steamy days with temperatures near 100F (37.8C) every day. Many people in the area endured more than a week without power, and we all gained a new appreciation for air conditioning.

Monday, July 16, 2012

First Quarter Moon

Moving Along the Terminator

The unusual clear, cool, low humidity weather on June 26 lingered from morning into evening. A nice first quarter Moon beckoned me to set up my Celestron-8 telescope and try some lunar imaging along the terminator. Good observing conditions don't last long in Lynchburg! About 30 minutes after starting work some clouds began drifting across the Moon. But I did get enough pictures to make this 9-image mosaic running down the length of the terminator. Notice the linear feature near the top, but ignore the imperfect section in the mosaic.
Can you find the fuzzy section? I hope not! (Click for full detail.)
This individual image shows the linear feature called the Alpine Valley. Notice the long shadows cast to the left by mountains below the Alpine Valley.
The Alpine Valley just left of center. (Click for full detail.)
Finally, this image shows Mare Serenitatis at upper right and an odd, oval-shaped depression called Rima Hyginus just left of center at the bottom:
The Apollo 15 landing site is near the mountain range on the upper left. (Click for full detail.)

Sunday, July 8, 2012

Late June Sun

Solar Images 6 Days After the Solstice

It has been over a month since I last used my solar telescope! After many, many cloudy days an unusually clear, pleasantly cool morning arrived on June 26. The Sun displayed only one relatively unspectacular sunspot on this magnificent morning, but there was also a new emerging sunspot near the Sun's limb and a nice pair of prominences. First, check out the prominences:
(Click for full detail.)
On the other edge of the Sun, almost diagonally opposite the prominences shown above, was this nice scene:
(Click for full detail.)
Moving around the limb to the left from the image above revealed sunspot group 1513 emerging onto the Sun's Earth-facing side in this mosaic of 3 images:
Sunspot group 1513 is at upper left. (Click for full detail.)
The combination of my DMK41 camera, Lunt 100 mm H-alpha solar telescope, and 2X Barlow lens produces an image size roughly 10 arc minutes by 7 arc minutes. The Sun's apparent angular diameter is about 30 arc minutes. In order to capture the entire solar disk I would have to combine about 4 slightly overlapping images in width, and about 5 slightly overlapping images in height. These 20 individual images could then be combined in a mosaic showing the entire solar disk. If I could ever complete this monumental task, the result would be an enormous, detailed image, perhaps 4500 by 4500 pixels, showing sunspots, filaments, and prominences over the entire Sun.

The largest mosaic I've so far produced included only 9 images, less than half the number required for a full disk image. Here are some problems I encounter when trying to make a mosaic:
  • Imprecise telescope mount movement is the biggest problem. The mount doesn't stop moving when I release the movement button. Instead, it continues temporarily drifting by unpredictable amounts. This makes it extremely difficult to cover the Sun with a precisely spaced patchwork of images.
  • Varying brightness of individual images is another problem. All image brightnesses have to be manually adjusted so the combined mosaic is a smooth blend with no obvious brightness changes on the borderlines between constituent images.
  • Image clarity varies across the mosaic if there is more atmospheric turbulence during one image than during another image.
  • Finally, solar features continuously change. If too much time elapses while capturing the 20 images, they may not blend smoothly on the edges because edge features in one image have changed by the time the neighboring image is obtained.  
The first picture below is a mosaic of 4 individual images. It shows sunspot 1512 nearly centered on the lower portion of the Sun. Only this one sunspot group was prominently displayed on June 26. The field of view here is 20.2 arc minutes wide by 6.8 arc minutes high. Notice the imperfect brightness blending in the lower right:
Sunspot 1512 nearly centered (Click for full detail.)
 Let's zoom in for a closer look and move down a bit. We see sunspot 1512 above the lower limb:
(Click for full detail.)
Finally, here's a detailed single image of sunspot 1512 alone:
(Click for full detail.)
It was nice to observe on such a pleasant day! I only wish more interesting solar features were present.

Monday, July 2, 2012

Korea Trip - Part 5

Transit of Venus

We planned our Korea trip to include observing the transit of Venus, an extremely rare astronomical event. Venus crosses the face of the Sun only twice a century! It won't happen again for another 105 years. Here's a diagram showing how this June's transit transpired.
I've been lucky to observe both transits this century, one in 2004, and the latest one just a few weeks ago. Neither was fully visible from Virginia, so I traveled long distances to view them. In 2004 I went to Italy with an astronomy tour group to observe the entire transit in perfect conditions from a site north of Rome.
Viewing the transit in Italy while wearing my special transit t-shirt
Conditions in Italy were absolutely perfect - clear, totally cloudless skies for the entire transit duration. Unfortunately, conditions were not so perfect for viewing the 2012 transit from South Korea. On June 6th, transit day in Deokpo on Geoje Island, the sky was covered with high, hazy clouds. Of course, with my typical astronomical luck, the sky was clear the day before and most of the day after. On June 6th the Sun was bright enough to show through the milky whiteness at times, but it was never entirely free from obscuring hazy clouds.

Around 6:30 am local time I gathered equipment and went to the roof of my daughter's 10-story apartment building. I hoped to use a mylar filter with either Keegan's binoculars or his camera. I also had my pair of 10 X 25 Coronado solar binoculars. First, I unsuccessfully tried Keegan's binoculars. It was impossible to steadily hold the filter in one hand and the binoculars in the other. The Coronado binoculars worked best, although the Sun frequently looked fuzzy through clouds. At about 7:20 am I first detected the black presence of Venus entering the Sun's limb. Soon after I attempted a photo using Keegan's Canon EOS Digital Rebel XTi equipped with a 300 mm telephoto lens. The camera was mounted on a good quality tripod, but I had to manually hold the mylar filter in front of the lens. It was extremely hard to focus. Here's the disappointingly fuzzy image I captured soon after Venus appeared on the Sun.
1/13 sec exposure at f/11 with 300 mm telephoto lens at 7:23 am
The mylar filter purposely blocks most of the Sun's light. It passes only a small portion in the blue end of the visible spectrum. Thus, my images have a blue-purple color. After Venus had fully entered the Sun's disk I tried another picture. Again, the image isn't sharp because hazy clouds masked the Sun. Focusing was very difficult.
1/10 sec exposure at f/14 with 300 mm telephoto lens at 7:46 am
The last image here is the best of my efforts. Clouds thinned briefly allowing better focus. Venus is sharper and three sunspots are barely visible. The sunspots look like tiny dark specks arranged along a line starting at Venus and proceeding diagonally downward to the right. The exposure time could probably be improved, but there was no time to try variations because clouds closed in again.
1/80 sec exposure at f/5.6 with 300 mm telephoto lens at 10:59 am
I didn't use my solar telescope to observe this event because it would have required hauling four big equipment cases and my laptop to Korea. I couldn't imagine putting this expensive equipment at risk on the long journey. Perhaps modern scientific observatories render amateur viewing on location obsolete. For example, magnificent instruments in the Solar Dynamics Observatory satellite continuously observe the Sun without any atmospheric interference. Images from this satellite are available to anyone, and the image quality far exceeds that of my pathetic images above. Here's just one example:
Transit image from the Solar Dynamics Observatory (Click for full detail.)
Astronomical observing is often a struggle. Obstacles abound. Unobstructed viewing space on the apartment roof was limited. Numerous wash lines strung across the roof blocked the view. When the Sun neared the zenith my attempt to observe from a horizontal position on a beach chair was blocked by a drying blanket flapping in the breeze above me. As noon approached the Sun was so near the zenith the camera tripod could not point towards it. I stopped watching at about 1:26 pm. Thickening clouds prevented viewing the egress. Nevertheless, it was a thrill to view this event, even under less than ideal conditions.

Finally, I can't resist including something from a talk I once gave to an astronomy group before the 2004 transit. In June of 1769 an astronomer with the astounding name of Maximilian Hell observed a transit of Venus from the island of Vardo off the coast of Norway. By a remarkable coincidence a total solar eclipse followed only 6 hours after the transit! Hell also observed this eclipse! When I read about this unlikely and spectacular pair of events it got me thinking about events that would be even more unlikely, but much more spectacular. Imagine the following sequence of astronomical wonders:
  • The sky is completely clear on transit day and the Sun is covered by several huge complicated sunspot groups as well as many filaments and big prominences along the solar limb.
  • Venus AND Mercury transit at the same time!
  • Shortly after the planets transit a total solar eclipse occurs! When the solar corona becomes visible during totality both Venus and Mercury are visible against the bright coronal background!
  • During the darkness of the total eclipse a beautiful comet (previously unobservable because of its proximity to the Sun) becomes visible near the Sun!
  • An auroral display becomes visible in the north while totality proceeds in the south!
  • A massive sporadic meteor shower with hundreds of meteors per minute becomes visible during the darkness of totality! 
Imagine astrophotographers frantically trying to capture images of all these wonders! Afterward they have ice cream.

People say I'm crazy doing what I'm doing
Well they give me all kinds of warnings to save me from ruin
When I say that I'm o.k. well they look at me kind of strange
Surely you're not happy now you no longer play the game

People say I'm lazy dreaming my life away
Well they give me all kinds of advice designed to enlighten me
When I tell them that I'm doing fine watching shadows on the wall
Don't you miss the big time boy you're no longer on the ball

I'm just sitting here watching the wheels go round and round
I really love to watch them roll
No longer riding on the merry-go-round
I just had to let it go

John Lennon