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Crescent Moon, Comet 46P/Wirtanen

Posted: 13 December 2018

Did not open the observatory on Sunday, 9 December 2018. It was very breezy that night. Monday, 10 December, was cloudy and windy. Cloudy skies continued until Wednesday, 12 December.

Open: Wednesday, 12 December 2018, 1812 MST
Temperature: 61°F
Session: 1314
Conditions: Clear, breezy

Equipment Used:
12" f/8 LX600 w/StarLock
2" 24mm UWA eyepiece

iPhone 8 Plus

SYNCed observatory clock to WWV.

1820 MST: LX600 ON, StarLock OFF, High Precision OFF.

Viewed the waxing crescent Moon, 102X.

Took this handheld iPhone afocal 102X photo of the Moon using the iOS app NightCap Camera (ISO 22, 1/500sec):


Next, updated the TLE for this night's excellent pass of the International Space Station (ISS). Mounted the D850 DSLR at prime focus of the 12" telescope. Focused on the Moon and locked the telescope primary mirror. Took this photo (1/320sec, ISO 400):


Compare the two images of the Moon. If the only camera you have is a smartphone, getting nice photos of the Moon through a telescope is certainly possible.

Unfortunately I did not complete the setups in time to video record the ISS through the telescope. So I watched it cross the sky with the naked eye. The space station was very bright as it passed near the zenith.

1851 MST: spotted Comet 46P/Wirtanen with the naked eye. I confirmed it with the 12x50 binoculars. Even with the moonlit sky the comet was very obvious if you knew where to look. (Unfortunately, while the comet will be getting slightly brighter over the next few nights, the Moon will also be getting brighter and closer to the comet's position in the sky. This will make seeing the comet with the naked eye more difficult.)

1855 MST: Wi-Fi ON. Used SkySafari 6 Pro on the iPhone to GOTO the comet.

1856 MST: Wi-Fi OFF.

The comet was visible in the D850 viewfinder.

1858 MST: StarLock ON.

Did some imaging of the comet. Autoguiding was somewhat erratic due to poor seeing. Decided to wait about an hour for the comet to rise higher in the sky (and the Moon to get lower).

1906 MST: StarLock OFF.

1917 MST: saw a Geminid meteor in the southern sky. It was a fast mover.

1925 MST: had the wife come outside so she could see the comet. She didn't see it with her naked eye (wasn't dark adapted) but was able to view it with 7x50 binoculars.

1934 MST: saw another Geminid meteor. This one was in the eastern sky.

2005 MST: StarLock ON.

Seeing was still not good but did get some good images of Comet 46P/Wirtanen. I took StarLock autoguided exposures at 60 seconds and 30 seconds using various ISO values. The comet's rapid motion trailed its image in the 60 seconds exposures. This is a 30 seconds, ISO 6400, prime focus image:


A slight tail is visible at 11 o'clock from the comet's nucleus.

This animation of four images taken at about 1 minute intervals (30 seconds, various ISO values) shows the comet's rapid movement:


2019 MST: StarLock OFF.

Removed the camera and viewed Comet 46P/Wirtanen, 102X. No tail was visible to the eye.

I then set up the D850 DSLR with 50mm lens on a camera tripod (no tracking) on the observatory patio:


I took several photographs of Comet 46P/Wirtanen near the Pleiades and Hyades star clusters. This image was taken at f/2.8, 5 seconds, ISO 12800:


If you look closely at the above image you can see some nebulosity around the Pleiades. That surprised me since the exposure was only 5 seconds. Here is a magnified view from the same photo showing the Pleiades and nebulosity:


2045 MST: LX600 OFF.

Close: Wednesday, 12 December 2018, 2052 MST
Temperature: 45°F
Session Length: 2h 40m
Conditions: Clear

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