Equatorial Seestar

 New Mounting Option

During the past year I saw so much information about using Seestar in equatorial mode that I decided to try it myself. Manufacturer ZWO offered a relatively inexpensive wedge compatible with Seestar's tripod, so I ordered the wedge and installed it as shown in the next picture.

The wedge allows one of Seestar's rotational axes to point at the north celestial pole. At my location the pole is 37.4 degrees above the horizon. This tilt is visible above. The long handle accomplishes the tilt aided by the angular scale shown below. The wedge also allows azimuth adjustment with the other graduated scale. I had to fully lengthen the tripod legs to keep Seestar from tipping over!

When one rotational axis is properly aligned with the north celestial pole, rotation about this axis can follow objects as they cross the sky from east to west due to Earth's rotation. Consequently, once an object is centered in equatorial mode only ONE Seestar motion is required to keep it centered. Without the wedge Seestar operates in altitude/azimuth mode where TWO motions are required to keep an object centered. So, tracking should improve by switching from altitude/azimuth mode to equatorial mode.

I have been using Seestar in altitude/azimuth mode for a couple years now. During every long exposure a significant number of 10-second subframe exposures are rejected due to tracking errors. Sometimes as many as 80 percent of the subframes are rejected! In this case only 20 percent of Seestar operation time is producing useable results! The best I've ever achieved was about 33 percent rejected frames. I hoped many fewer rejected frames would result from improved tracking in equatorial mode.  

I had to wait several weeks for clear skies to use equatorial mode for the first time on April 14th. The first target was galaxy M51 in Ursa Major. Inevitable first time fumbling and inefficiency caused more than an hour of wasted dark time. With everything finally aligned and M51 centered I initially tried taking 20-second subframes instead of my usual 10-second subframes. It was disappointing to see roughly half of these 20-second frames rejected for poor tracking. I stopped the 20-second exposures and restarted using 10-second exposures instead. What a difference! Now no frames were being rejected - not one single rejection!

I wanted to try an exposure of several hours, but, unfortunately, the sky became increasingly hazy from wildfire smoke after midnight. I had to stop the exposure after 85 minutes. Incredibly, the entire 85 minutes produced useable results! Seestar produced 510 useable subframes with no rejections! The next image shows the result. (Click on the image to enlarge.) Notice small fuzzy elliptical galaxy NGC5198 toward the left edge.

As years go by more satellite trails and airplanes interfere with astrophotography. Although an airplane passed through the scene as shown below, I was able to manually remove the trails to produce the previous image.

This initial result made me anxious to try much longer exposures. If no subframes get rejected, I might be able to get up to eight-hour exposures of some objects.

Six days later on April 20th another clear sky opportunity arose. Having overcome my beginner mistakes made while setting up on April 14th I was much more efficient initiating equatorial mode. My target this time was galaxy M101 in Ursa Major. I was able to let Seestar run from just before 11 pm (EDT) to about 5:20 am when the northeastern sky was just beginning to brighten before sunrise. The result was a 397-minute exposure (6 hours 37 minutes) my longest exposure yet. This time 2,382 ten-second subframes were useable and only one was rejected!

This long exposure produced the next image showing M101 much better than a previous 90-minute exposure made in 2024. In particular, the outer spiral arms are brighter, and the inner portions show more detail. Notice fuzzy galaxy NGC5474 near the upper right edge and dimmer small galaxy NGC5477 near the top edge.

Just as with the M51 image, satellite tracks ran through the picture as you can see in the next image if enlarged to full size. I manually removed the tracks for the image above.

Sky transparency varied throughout the M101 exposure. It's rare to get truly dark sky at my location.

Despite some modest moonlight on April 22nd the sky was cloudless. My target this night was edge-on galaxy NGC4565 in Coma Berenices. After a late start I was able to get a 297-minute exposure (4 hours 57 minutes) before the galaxy set behind a nearby roof at about 5 am. On this night 1,786 10-second subframes were useable. 83 subframes were rejected because the galaxy was blocked by the roof near the end. The long exposure revealed some detail in the outer arms as you can see below if you enlarge the image. Notice small galaxy NGC4562 to the upper right and brighter fuzzy galaxy NGC4555 near the left edge.

I look forward to trying long exposure equatorial mode along with mosaic mode on nebulas I've previously imaged.