As an avid planetary imager, I've had my fair share of accomplishments, but Mercury has always eluded me. One of my goals for 2025 was to end that frustration and finally capture an image of the smallest planet in our solar system. This current mid-to-late August apparition offered the best opportunity of the year. Fall morning apparitions provide the most favorable geometry, with the planet's solar separation translating to vertical height above the horizon due to the inclination of the ecliptic in the autumnal pre-dawn sky.
Due to the trees (which need trimming this winter), Mercury must reach about 40° altitude to clear them, necessitating a daytime observation. That’s not too difficult for Venus, but it posed a bigger challenge for Mercury, which isn’t visible in the finder scope. Fortunately, the ALPO webinar last spring on daytime planetary imaging provided valuable tips and encouragement, confirming that I had the equipment and skills needed for success.
The weather from spring through much of summer this year was dismal. Clouds were the norm, and even when the skies cleared, seeing conditions were often below average or marred by smoke from the Canadian wildfires. So when a forecast for below-average transparency but average seeing presented itself on August 17th during the favorable morning apparition, I decided to commit to an imaging run.
I stepped out at 4 a.m. to align my telescope, only to be greeted by a strong haze that limited visibility to 2nd magnitude stars. By 9 a.m., the clouds had worsened, making it difficult to even spot the fat crescent Moon. However, I managed to bring Mercury into the camera’s field of view and run some captures. The resulting image showed a chubby crescent phase with little to no discernible albedo features - a technical success, but not truly satisfying.
With a forecast for better transparency and above-average seeing on the morning of Saturday, August 23rd, I decided to give it another shot, with Mercury just past dichotomy. I set up my scope to cool and went to bed Friday evening, again waking at 4 a.m. to align the CGX-L mount. The alignment was good enough to bring targets into the low-power view. After aligning, I did a couple of lucky imaging runs on Saturn in color under pretty good seeing conditions. I then moved on to Jupiter for more practice and captured an IR image as dawn approached.
Then, despite being plugged in, my laptop died unexpectedly. Clearly, the recently purchased AC adapter will need to be returned. Frustrated, I took it back upstairs to charge while waiting for Mercury to clear the tree line at 8 a.m.
Returning to the driveway, I was pleased to see clear blue skies with only minor clouds. The morning breeze was gentle, and transparency and seeing conditions seemed promising. I started by slewing to Venus to practice my hand controller motions, ensuring that one short press to the right and 2–3 presses up would bring the slewed object into range.
Finally, I slewed to Mercury for the moment of truth—and the planet popped into view! Initially, it looked turbulent, but after adjusting the focus manually and using SharpCap’s Fourier Detail Detection routine, I was able to achieve a good focus. The strong surface brightness of the innermost planet allowed for high frame rates, and I adjusted the exposure, gain, and region of interest to achieve over 100 frames per second.
The planet danced wildly due to the rising Sun and atmospheric currents, with only fleeting moments where the half-moon phase was discernible. I captured a series of three 3-minute videos at 3ms exposure and a gain of 180, followed by experimentation with higher gain and lower exposure to increase the frame rate. In total, I captured about 20 minutes of video.
Processing the data later that day revealed good-quality images, with sufficient seeing to produce a reasonable stack. I whittled down nearly 64,000 frames from the 3ms videos to create a nice image. I also experimented with AstroSurface for the first time to sharpen the result and was pleased with the tool.
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While this face of Mercury lacked high-contrast albedo features, my image showed a mottled surface, reflecting large-scale features. After all, at only 6.6 arcseconds in size, I’m targeting something roughly the size of a tomato seed viewed from across a football field! With this success under my belt, I’m looking forward to making Mercury imaging an annual event—weather permitting!
