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Comet 46P/Wirtanen

Posted: 27 November 2018

Sunday, 25 November 2018, was clear but I skipped opening the observatory that night as Monday would be a day full of activities. Monday, 26 November, was cloudy until mid-afternoon.

Open: Monday, 26 November 2018, 1811 MST
Temperature: 65°F
Session: 1310
Conditions: Clear

Equipment Used:
12" f/8 LX600 w/StarLock
2" 24mm UWA eyepiece
12x50 binoculars


1817 MST: LX600 ON, StarLock OFF, High Precision OFF.

Viewed Saturn and two of its moons, low in the southwest, 102X. Then viewed Mars, 102X. It was fun to view Mars a few hours after the NASA InSight mission successfully landed on Mars.

SYNCed the AutoStar on the star Fomalhaut in preparation for imaging Comet 46P/Wirtanen later. Prepared the D850 DSLR for imaging.

1834 MST: Meade Stella Wi-Fi Adapter ON.

Used SkySafari 6 Pro on the iPhone to GOTO Comet 46P. The comet was still very low in the southeast and behind a tree. However, it was visible in the 12" telescope, 102X. The coma was larger than I expected based on what I observed the last time I viewed the comet on 31 October 2018. I began waiting for the comet to rise higher in the sky. 1838 MST: Wi-Fi OFF.

1856 MST: after doing some searching I finally viewed Comet 46P/Wirtanen using my Vortex 12x50 binoculars. The coma appeared really large and was surprising bright, although not yet at naked eye visibility. That comes in December (hopefully). No tail was visible in the binoculars.

1903 MST: the comet was now above the tree. It was nicely visible in the Orion 9x50 finderscope and at 102X through the 12" telescope. I still wanted it higher in the sky before starting imaging.

1947 MST: breezes began increasing.

1952 MST: mounted the D850 DSLR at prime focus of the 12" telescope, focused on the star Fomalhaut, and locked the mirror using the ScopeStuff LX600 Primary Mirror Lock.

2000 MST: Stella Wi-Fi Adapter ON.

Used SkySafari Pro on the iPhone to GOTO the comet. I could not see the comet in the camera viewfinder. 2002 MST: Wi-Fi OFF.

2003 MST: StarLock ON.

Did a framing test exposure (1 minute, ISO 3200). Using the image as a guide I was able to locate the comet in the D850 viewfinder and center it. I then did several 1, 2, and 3 minute exposures and ISO 3200 and ISO 5000. The comet's rapid motion caused the 2 and 3 minutes exposures to show trailing of the comet. Poor seeing and the comet's low elevation the sky caused StarLock autoguiding challenges.

2038 MST: after taking several images I finally got a good image of the comet, StarLock autoguided, 1 minute, ISO 5000, White Balance 4000K, slightly cropped:


A slight tail from Comet 46P/Wirtanen is visible in the image at 11 o'clock from the comet's nucleus.

2041 MST: StarLock OFF.

The eastern sky was beginning to brighten from the rising waning gibbous Moon.

2054 MST: LX600 OFF.

Close: Monday, 26 November 2018, 2102 MST
Temperature: 53°F
Session Length: 2h 51m
Conditions: Clear, breezy

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