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Lunar Conjunction with Jupiter

Updated: Apr 18, 2023

2023.02.22 - Our Solar System is vast and wondrous, but its immense scale also makes it largely imperceptible to mankind. Fortunately for us, it is also equally predictable in its adherence to the inescapable laws of physics, so every once and a while there is a conjunction between the small celestial objects that define our local reality and the greater system beyond it that helps bring our Solar System into focus. This week one of those moments occurred as the Moon and Jupiter's orbits neared each other from the perspective of Earth.

As with most nights around here, the sky was somewhat clear as the sun began to set, but clouds quickly began to smother the small groups of visible stars in the sky. I knew that my opportunity to shoot the conjunction would be ephemeral, so I quickly grabbed trimmed down astro setup of my camera, a tripod, a geared head, and a cable release and headed to the mosquito infested backyard. I estimated that the proximity of Jupiter to the Moon was about right for around a 1000mm focal length, so I a clipped the 2X teleconverter on the 500mm and hoped for the best. I was happy to find that the framing was almost perfect, so the above image is only a slight 2:3 ratio crop of the original image.

23.04.18 Update: I uploaded a new image above because the previous image was marred by blocky artifacts in the black background. It took a while to troubleshoot, but I think I have found the problem and I hope this may help others. This image was originally 16 bit, so when I dropped it down to a 2560 pixels wide, medium-quality jpeg it wrecked the nuanced gradients in the black space. These blocky artifacts were most obvious on a color-corrected 4k monitor (such as the one I primarily use for processing images), but I found that it was largely unnoticeable on my lower resolution monitors to include my phone. Since I can't anticipate how people will view this site, I'd rather address the issue than ignore it. The current fix appears to be to down-sample the 16-bit image to 8-bit before exporting to a lower-compression/higher-quality jpeg. On my website at least, this seems to help, but I will need to test it on social media in the future.

At this focal length without tracking, the Moon and Jupiter moved very quickly through the frame. I only had time to take a few shots before needing to reframe and wait again for the rig to settle between gusts of wind. That's the beauty of the geared head though, as it makes it much easier to move in the x and y direction to track the angular trajectory of celestial targets than a ball head.

Even at 1000mm, Jupiter and its moons are only barely visible as blobs of light

Even at a mere 7% of its normal illumination, the difference between the dark and light portions of the moon was considerable, and was different still from the exposure required for Jupiter and its moons. In the end, I used 3 photos ranging from 1.3 seconds to 1/40 seconds of exposure (around f14 and ISO 3200) and merged them in Photoshop to create this HDR image. It would have been better if I had used a star tracker to take longer exposures at lower ISO, but the time required to level, polar align, and guide that setup would have likely taken longer than the sky was clear. This even was only visible for a few hours, so trying again on another night was not an option. You take what you can get with the weather around here, so I was happy to get what I could before the entire sky was lost in a dome orange/brown water vapor.

The skies over the Gulf Coast are volatile and largely hostile to astrophotography, but I am stubborn, so for the time that I live on the outskirts of the glowing megalopolis of Houston, I will continue to point my camera at the wonders hiding in the sky above whenever I can.

© 2017-2023 Shaun C Tarpley Photography

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