Sunspots Across the Sun

Brief Observing Window

I've waited two months for a suitable day for solar imaging. The dawn sky on August 9th was completely clear. Cloudless conditions promised to hold for a while, so I hurriedly set up equipment to take advantage of this rare opportunity. The temperature was in the low 70's when I began capturing images at 8:42 am EDT. There was no wind and seeing conditions were initially excellent.

My first task was to gather enough images to construct a mosaic showing features across the solar disc. On the following 19-panel mosaic seven significant sunspot umbras are visible along with a few white active areas and some filaments. (Click on the  image for an enlarged view.)

The major sunspot complex near the right limb contains sunspots 4165 and 4168. You can see complicated structure around this pair along with several white flare areas which were active during image capture. Examine other active areas in the enlarged image to see magnetic arches and a split umbra in sunspot 4169 left of center.

A beautiful prominence display added to the solar scene this day. The previous image was processed to make prominences more visible in the next image below. On the enlarged image you can see a small filaprom, the transition between prominence and filament, on the left limb above center. A double spike prominence on the lower left limb was changing while I gathered images. Several smaller spikes are on the right limb. 

After completing the disc mosaic above I made prominences brighter by increasing the camera's gamma value. The next four-panel limb mosaic shows prominences more clearly. In particular, notice the linear segment suspended high above the double spike prominence in the lower left.

The magnified image below shows the suspended prominence more clearly. When I first imaged this portion of the Sun only one spike was present. The next time I came to this spot there were two spikes. So these explosive emissions were happening on the scale of 10 minutes or so. Clouds prevented returning here to make a time lapse video of the eruption.

Another four-panel mosaic shows prominences on the Sun's right limb. 

While capturing the last image for the previous limb mosaic I noticed thin clouds encroaching from the west. Clouds and haze began to quickly build thereafter. The clear observing window had lasted only 41 minutes! Seeing also deteriorated drastically, so it was time to shut down. Such is life in southeastern Virginia. 

 

Hot, Humid July Nights

Globular Cluster Pairs

July in southeastern Virginia brings steamy cloudy nights. There's little opportunity for celestial observing, especially near full Moon. Brief clearing on July 23rd and 25th allowed only a few hours to employ my Seestar50.

Over the past year I've used Seestar to image almost all relatively bright dramatic objects within its range. It's time to try something different. Lately, I've been using Seestar's mosaic mode to capture more than one object in the field of view. One example below is a globular cluster pair in Sagittarius captured on July 23rd with a 40-minute exposure. Enlarge the next image and scroll around to see large globular cluster M22 on the bottom and small, undistinguished globular cluster NGC6642 near the top. An attractive five star group near the right edge contains colorful 5th magnitude red supergiant star, 24 Sagittarii. The crowded Milky Way star field provides a busy background. M22 is separated from NGC6642 by 67 arc minutes. 

What explains the remarkable apparent size difference of these two globular clusters? Answer: M22 is both intrinsically larger and closer than NGC6642. M22 is 97 light years in diameter and 10,400 light years away. NGC6642 is 45 light years in diameter and 26,700 light years away.

Mosaic mode was not required to capture another globular cluster pair in Sagittarius separated by only 16 arc minutes. In the next 10-minute exposure NGC6522 on the right and NGC6528 on the left appear in front of Milky Way stars and some dark nebulosity. The brightest star at the bottom is Alnasl, the 3.6 magnitude star at the tip of Sagittarius' teapot spout.

These disappointing clusters have modest diameters and are relatively far away. NGC6522 is 25,000 light years away and has a diameter of 69 light years. NGC6528 is 26,000 light years away and has a diameter of 37 light years. The sky became increasingly hazy on July 23rd, so I had to stop imaging after obtaining the previous two images. The observing window was open for only about two hours.

At twilight on July 25th the sky seemed nicely clear so I attempted to capture both nebula M17 and open cluster M18 together in mosaic mode. The upper portion of the next 58-minute exposure shows M17, The Omega Nebula, together with open star cluster M18 in the bottom right. M18 is 56 arc minutes from M17. I was disappointed that M18 is only a modest grouping a few stars. I was also disappointed by the sky's increasing milky haze which caused me to limit exposure time and quit early. Once again, the observing window was only about two hours long. 

There are a lot of clouds in July! They obstruct astronomical observing, but often bring late afternoon showers and thunderstorms. Sometimes, conditions are right for rainbows! On July 27th the Sun was still high above the horizon and the rainbow in the next image was correspondingly low. This rainbow was unique because its left end extended down in front of trees about a quarter mile away. I had never seen a rainbow this close to my observing spot before.

Four days later on July 31st a partial rainbow appeared under clouds almost in the same location as the previous rainbow. In the next image you can see its left end behind the trees this time.

I hope for fewer clouds in September and October.