Saturday, April 30, 2016

Solar Granules

Sunspot 2529 - Two Views

During the morning and afternoon of April 16th observing conditions were nearly perfect: clear sky, calm wind, temperature near 60 degrees, and decent seeing. My goal was to image significant sunspot 2529 in both hydrogen alpha and white light.

I began with the hydrogen alpha view. The first image below is an 8-panel mosaic of the Sun's western limb with sunspot 2529 nearby. Some modest prominences adorn the limb. (Click on the images for a larger view.)
The next image is a closer view of the sunspot showing detail in the dark umbra and white active areas near the spot.
Small sunspot 2532 had just emerged on the eastern limb where a spiky prominence can be seen in the next 4-panel mosaic.
Beautiful observing conditions continued into the afternoon, so I mounted my Stellarvue 130mm and tried white light imaging for the third time. Better seeing and better filters improved my results. The next image was my best effort. It was done using a Herschel wedge with a 5X Barlow lens combined with stacked neutral density and uv/ir filters. Detail in the umbra and penumbra is pretty good. Surface granulation is plainly visible, but not as sharp as the umbra detail. This is clearly superior to my previous white light images.
Since the sunspot was getting near the western limb on the right side of the image, the granules there are smeared out. Granule boundaries are sharpest in the center of the solar disc to the left.

I took an image of granules in the center of the disc where no sunspots existed so I could compare my image with an image of the same region taken by the Solar Dynamics Observatory orbiting above the atmosphere. My image is first below followed by the SDO image. I tried to get the image scales roughly equal.
The clarity and sharpness of the satellite image is obviously superior to my image, but I'm getting closer to respectability. My image also contains noticeable distortion in the lower corners. Perhaps I didn't quite get the center of the Sun, or, maybe, it's an optical distortion. I'll keep trying to home in on the correct combination of filters, exposures, and Barlow lenses.

Friday, April 22, 2016

Magnetic Pinwheel

Worthy Sunspot Finally Appears

Solar activity continues to slide toward sunspot cycle minimum. For months now only modest, solitary sunspots have appeared. Finally, on April 10th, a good-sized sunspot, the largest of 2016 until then, came into good view. I decided to set up my telescope early in spite of the cold 40-degree temperature to take advantage of predicted good seeing. There was little wind, and no clouds, but seeing was not as good as predicted.

The first image below is a 6-panel mosaic showing solitary sunspot 2529 some distance from the eastern limb. The sunspot occupies center stage within a magnetic pinwheel of swirling gases. As you can see, no significant prominences or filaments were present in this quadrant of the Sun.
The sunspot umbra showed interesting structure. (Click on the image for a larger view.)
After capturing images in hydrogen-alpha, I dismounted my Lunt 100mm solar telescope and mounted a 130mm Stellarvue refractor. I hoped to image the sunspot in white light with new filters in place. A 1.8 neutral density filter and a uv/ir filter were installed in the light path. These filters attenuated sunlight enough so I could use suitable exposure times. The first white light image below shows decent detail in the sunspot umbra and penumbra, but surface granulation is washed out.
Many sunspot pictures I see online are processed to make the umbra completely black with no gradation of blackness. The next image is processed this way. It shows the granulation a little more clearly.
In the last two images I noticed how granules are smeared and indistinct in the upper left nearest to the solar limb. Apparently, this loss of detail near the limb happens in even the highest resolution images made by the orbiting Solar Dynamics Observatory, so this effect can't be caused by poor seeing or faulty image processing. The surface to the right of the sunspot shows evidence of granulation, particularly in the second image, but I'm disappointed in the lack of sharp detail. I think a combination of poor seeing and small image scale may be responsible for the blurry appearance .

Thursday, April 14, 2016

Telescope Orgy

Solitary Sunspot

March 29th was a completely clear day, but chilly, and very windy. Morning temperature hovered near 55 degrees. Seeing was not particularly good, but there were occasional decent patches of steady images. It remained wonderfully clear all day, so I actually used my telescopes in the morning, afternoon and evening!

Daytime wind was a real problem. Springtime is often surprisingly windy here in Williamsburg. My laptop normally sits in a cardboard box which serves as a sun shield during daylight. Usually, the laptop alone is heavy enough to anchor the cardboard box when it's windy, but this day's wind was particularly strong. Taking the strong wind into account, I put one of my equipment cases on top of the laptop to add more weight and ensure the cardboard box would stay put in the wind while I continued to set up. Shortly after I turned away to get more equipment I heard a sickening crash and watched the box, laptop, and equipment case tumble off my observing table and fall to the ground after a blast of wind. The box with its contents then rolled over on the ground. I felt ill. Fortunately, in spite of the horrendous fall, no harm was done. Incredibly, the laptop still functioned normally. After this near disaster I ditched the box. It was catching too much wind. I held a blanket over my head to shield the laptop for the rest of the morning.

Morning observing began with my Lunt 100mm hydrogen-alpha solar telescope. Only one solitary sunspot was visible along with a couple of modest filaments. The first image below shows lonely sunspot 2526 in good detail with a bright active area to its left. The image is processed to preserve the dark gradations in the umbra which you can see better if you click on the image for a larger view.
Next is an image of the two modest filaments also present.
After finishing hydrogen-alpha solar imaging in the morning, I put the Lunt telescope away and mounted my new Stellarvue 130mm refractor. In the afternoon I installed a new Lunt Herschel Solar Wedge on the Stellarvue. The wedge is used for solar observing in white light. I hoped for detailed views of photospheric sunspots and surface granulation with the wedge.

In addition to the wedge prism itself, the apparatus includes a neutral density filter and a polarizing filter to dim the Sun's light enough for comfortable viewing. Even with filters fully engaged the eyepiece view was quite bright. Solitary sunspot 2526 showed well, but the surrounding surface granulation was not particularly sharp. Granulation was just barely visible, only hinting at what would be visible with better seeing and, perhaps, better filter combinations. I will have to experiment with an additional neutral density filter in the future.

Next, I tried imaging with the solar wedge. Sunlight reaching the camera was much too bright. Even with zero gain and very short exposure times the images were nearly overexposed with an extremely narrow histogram. I've ordered a UV/IR filter and an additional neutral density filter which, I hope, will further dim the sunlight and allow better imaging in the future.

The image below is the best image I obtained with the wedge. It's colored to approximately match what I saw in the eyepiece. Because I imperfectly processed the image to bring out details in the umbra, there is some distortion in the border of the umbra. Granules are visible on the surface all around the sunspot, but the granule boundaries aren't sharp. (Granules are the tops of upwelling fountains of hot gases continually rising and falling in the solar photosphere.) This image falls far short of the best photospheric sunspot images I've seen. I hope to improve image quality in the future.
Finally, in late afternoon, I took off the solar wedge and left the telescope mounted so I could return for an evening session after dinner. The wind finally died down after sunset, and the sky remained completely clear.

As darkness fell I restarted my Paramount mount and synchronized on the star, Rigel. Then I constructed and applied a 6-star TPoint model in an attempt to increase pointing accuracy. (A TPoint model is created by commanding the telescope to point at selected stars. The observer manually corrects the pointing inaccuracy for each of the stars. The computer then makes a mathematical model based on the recorded inaccuracies. The mathematical model is then applied to correct future pointing inaccuracies.) The TPoint model resulted in good, but not perfect pointing. Every target I slewed to throughout the evening was somewhere in the eyepiece field of view, but never exactly in the center of the field.

For the next few hours I looked at 25 objects, including 15 Messier objects. It was fun trying different eyepiece combinations and enjoying the beautiful views of star clusters, double stars, and a couple of galaxies. Unfortunately, many neighbors' lights were glaring into my yard this evening. A solar observing hood draped over my head helped block the offending lights while I looked through the eyepiece, but my night vision was completely destroyed every time I emerged from under the hood. My new red light headlamp and adjustable observing chair were wonderfully helpful for night observing. Sometime before midnight I took my equipment down. I was tired, but content after a full day of fun astronomy. 

Wednesday, April 6, 2016

Bad Seeing

Limited Results

On March 18th only a few tiny clouds scattered across a clear sky. The temperature was a comfortable 66 degrees, but wind gusts increased through the afternoon. I got a late start at 2:33 pm. The seeing was particularly bad this day, possibly the worst I've ever seen since moving to Williamsburg. It was hard to achieve good focus because the image on my laptop was so blurry. Consequently, most of my images were very poor quality.

Only one 6-panel mosaic came out reasonably well. It shows sunspot 2519 approaching the western limb with a nice prominence nearby and a couple of modest filaments to the sunspot's left.
Portions of this mosaic are blurry. The sunspot and its umbra lack detail. Spicules on the limb are smeared and indistinct. I hope this extremely bad seeing doesn't continue in the coming warmer months. Perhaps this day was just unusual bad luck. 

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