August Seestar

Summer Celestial Scenes From My Backyard

Although cloudless sky was a little hazy on August 16th, none of my neighbors had turned on glaring spotlights. It seemed like a good opportunity to use Seestar, even if conditions were imperfect.

In spite of haziness, I was able to capture a nice mosaic image of galaxy NGC6946 and open cluster NGC6939 together in the same field of view. These objects in the constellation Cepheus are separated by only 39 arc minutes (0.65 degrees). The following image is a 45-minute exposure with detail good enough to be viewed at full size. The star cluster, only about 5,900 light years away, is a member of our own Milky Way galaxy. On the other hand, galaxy NGC6946, about 22 million light years away, is far beyond the Milky Way. These objects just happen to be nearly along the same line of sight from our point of view.

I next tried to image nebulosity in Sagittarius. After engaging the light pollution filter I could only manage the following 30-minute exposure before increasing haziness made the sky milky white. At that point it was time to quit this August 16th session.

There are at least four named nebulae in the next picture. The most prominent red emission nebula just above center is IC1284. The dim red glow just to the upper right of IC1284 is another emission nebula, IC1283. The silvery white glow surrounding two stars in the center is reflection nebula NGC6595. Enlarge the image to see the faint presence of a tiny dark nebula within NGC6595's white glow. Another small white reflection nebula, NGC6589, is located to the upper right of NGC6595. Diffuse red Milky Way glow spreads across the bottom of the frame. As always, I'm disappointed by the dull red color produced by Seestar.  

A new Moon and clear sky beckoned on August 22nd. I began by targeting the Cave Nebula, Caldwell 9, in Cepheus using mosaic mode and the light pollution filter. Although I was able to get a 70-minute exposure, the nebula seemed dim. It might have been better to try the Cave Nebula alone without mosaic mode. The dark cave entrance does show up, but surrounding nebulosity is very faint.

Mosaic mode allows a field of view large enough to include the entire Andromeda Galaxy, M31, in Pegasus. My previous images of M31 included only segments which I unsuccessfully tried to blend together in a panorama. Mosaic mode allowed the whole galaxy to appear at once in the following 68-minute exposure. During this exposure a powerful neighbor light was suddenly turned on. I rushed inside to get a card table which can be set up to block the glaring light from hitting Seestar. Looks like the offending light didn't ruin this image of M31 and its two satellite galaxies.

Clear sky lasted well after midnight. I plugged a power cord into Seestar to recharge the nearly depleted battery and moved to a new target, the Pelican Nebula, IC5070, in Cygnus. The pelican's head and long beak extend diagonally downward from right to left in the following 60-minute exposure with light pollution filter. Bright blue star 57 Cygni sits to the left of the pelican's upper beak. Another bright star, 56 Cygni, is on the pelican's right side. The dull red nebula color is, again, disappointing.

With a few hours remaining before dawn I took a few images of planets Neptune and Uranus. A future post will describe the surprising details I saw!
 

 

Venus and Jupiter Dance

Conjunction Before Dawn

The two brightest planets had a close conjunction on August 12th. Three days before closest approach I took the following picture before dawn from my back yard patio at 5:44 am EDT on August 9th. Cloud free sky is rare here in southeastern Virginia, so I thought this might very well be the best conjunction image I would get. 

Venus (magnitude -4) is the brighter dot above dimmer Jupiter (magnitude -1.9). The planets were separated by 2.9 degrees. At this point in their orbits Venus was 10.14 light minutes from Earth, and more distant Jupiter was 49.68 light minutes from Earth.

Much to my surprise, the sky was clear again at 5:44 am on the next morning, August 10th. In the next image you can clearly see planet spacing had diminished. Venus was still above Jupiter, but the separation had diminished to 2.03 degrees. During the previous 24 hours Venus had receded from Earth to a distance of 10.19 light minutes while Jupiter had come closer to a distance of 46.61 light minutes.

What is happening here? We are looking from Earth toward Venus and Jupiter across the plane of the solar system. Near dawn the Sun is below the horizon, and the planets are west of the Sun above the horizon.

Earth, Venus, and Jupiter all orbit the Sun and we are viewing the conjunction from a moving Earth. When viewed from above the solar system (looking down on the Sun's north pole) all the planets are orbiting counterclockwise. They're all in separate nearly concentric curved lanes. Rapidly moving Venus (on an inside lane) is moving away from our slower moving Earth (on an outside lane). Venus is beginning to approach the Sun from our viewpoint, and we'll eventually see it pass behind the Sun. So Venus is receding from Earth, getting smaller, and nearing the dawn horizon as it approaches the (below horizon) Sun.

On the other hand, Earth (on an inside lane) is overtaking slower moving Jupiter (on an outside lane). Jupiter is getting closer to Earth as Earth catches up to Jupiter. From our point of view Jupiter had recently passed behind the Sun and is now swinging around its orbit increasing its angular separation from the Sun. So Jupiter is getting higher above the dawn horizon as it separates from the Sun. Venus and Jupiter are heading in opposite directions relative to the horizon. Venus starts out above Jupiter, but, eventually, Venus sinks and Jupiter rises, so they switch places. 

With naive optimism I hoped to show the daily decrease in separation over the next two days. Of course I should have expected disappointment. Annoying clouds ruined the view on August 11th! In the next image you can see a cloud gap. Unfortunately, Venus and Jupiter were located above the gap. 

Clouds again interfered on August 12th, the day of closest approach. This time, fortunately, the cloud deck was thin enough to allow bright planets to shine through. In the next picture you can see brighter Venus beginning to drop below Jupiter. The angular separation had now decreased to 52 arc minutes or 0.87 degrees!

The plane of Earth's orbit projected against the sky is called the ecliptic. On August 12th Jupiter was nearly in Earth's orbital plane - only 3.83 arc minutes or 0.06 degrees below (south) of the ecliptic. Venus was 55 arc minutes or 0.92 degrees below the ecliptic. This difference in ecliptic latitude accounts for nearly all the 52 arc minute separation. What about ecliptic longitude? Jupiter's longitude was 104.1 degrees and Venus'  nearly identical longitude was 104.28 degrees.

On August 12th Venus had receded further to 10.3 light minutes away and Jupiter had approached to within 49.46 light minutes of Earth. 

August 13th viewing conditions were hopeless. A low impenetrable cloud deck blocked everything. 

On August 14th conditions were similar to the previous picture, so it wasn't worth taking another picture of blank sky.

Before twilight on August 15th the dark sky was momentarily clear. I quickly took a photo and went inside to wait for twilight to grow. Only a few minutes afterward the sky became completely overcast! So the next image below was the best I could get on August 15th. You can see brighter Venus was now well below Jupiter. The angular separation had increased to 3.18 degrees. Venus had receded to 10.46 light minutes away and Jupiter's distance had decreased to 49.24 light minutes.

Clear twilight sky finally returned on August 16th. The planets had now separated further by almost a full degree to 4.13 degrees as shown in the next image. Venus receded to 10.51 light minutes from Earth and Jupiter, at 49.16 light minutes, continued to diminish its separation from Earth. 

While the sky was mostly dark before twilight on August 16th I used my camera's night mode to take the next picture.

The image scale above is wider than all previous pictures. You can see how the entire Venus/Jupiter planet dance took place within the constellation Gemini. Gemini's twin stars, Castor and Pollux, are left of the bright planets. (Pollux is below Castor.) Orion was rising above trees on the right. If you don't get up before dawn, you miss beautiful scenes like this one. I get up so you don't have to!

Before dawn on August 18th the Moon joined the planet dance. I used night mode again to capture the next image with the same image scale as the previous picture. A neighbor's unfortunate spotlight interfered some, but not enough to ruin everything.

It would have been nice to follow the Moon's approach toward the planets over the next three days, but completely cloudy skies made this impossible.

To see how the planets moved without cloudy interruptions I used Sky Safari 6 Plus to create an animation running from August 9th to August 20th. The animation steps forward one day at a time to show the predawn scene at 4:44 am EDT each morning. (To see the video properly click the full screen icon in the lower right on the video.) 

Notice how Jupiter lies almost exactly on the yellow line representing the ecliptic. The Moon makes an appearance in the last frame on August 20th making an attractive grouping with Venus and Jupiter. Also, notice how the stars get higher above the horizon each day as they rise approximately four minutes earlier each day due to Earth's orbital motion. 

It's fun to watch the solar system in motion when clouds don't interfere.

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.