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Strange Conjunctions: Mercury, the Moon and Uranus

April 23, 2012  •  Leave a Comment

An astronomical conjunction is a visual encounter between two or more celestial bodies as seen from some location on Earth. Conjunctions between the Moon and some stars or a planet are very common. Conjunctions of two ore more planets are also common. Some conjunctions are particulary bright like the Venus - Jupiter encounter on March 2012. On the other hand some conjunctions are quite rare or strange, this is about one of the rarest conjunctions I've photographed.

The Moon, Mercury and Uranus Annotated On April 18th 2012 just before dawn the Moon, Uranus and Mercury were in the same area of the sky. Both Mercury and Uranus are difficult planets for visual observation making this a very strange event. Mercury is always close to the Sun, the planet makes a few apparitions at dawn or dusk every year, from my location at the south hemisphere mercury rose above the East horizon at 5am and was visible until 7am a few minutes before sunrise. Uranus is barely visible with the naked eye but when you have a reference like the Moon and Mercury here it is doable. Making the conjunction better the Moon was a thin waning crescent displaying a nice earthshine. This annotated photo also shows Tx Psc, a very strange star, more on that in a few paragraphs.

The Moon and Mercury Over Buenos Aires Mercury and the Moon high in the sky before sunrise. Uranus was no longer visible to the naked eye. This photo shows how high Mercury can be seen from the South Hemisphere at the right time of the year. Almost 20 degrees high with the Sun yet below the horizon. Mercury was at maximum elongation exactly on this day.

The Circlet and the Carbon Star This photo shows the Moon and Mercury on the right. The Moon was in the middle of the asterism called "the circlet" in Pisces. If you look at the large version of the photo you will notice a small red dot just below the moon. That's not a bad pixel! It's 19 Psc or Tx Psc, a Carbon Star. Carbon stars are the reddest stars in the night sky, they are dim and difficult to see but this time the moon was a wonderful reference.

Conjunction and Circlet The circlet asterism is clearly visible here and Mercury is to the right. Uranus should still be visible but really small in this photo. The glow on the horizon was more intense from the impending sunrise. 

Mercury - Moon Conjunction The Moon is still nice and clear, mercury barely visible and sunrise is just about to happen.

From all the conjunctions that can be seen with the naked eye I think that a Mercury - Uranus pairing is probably the strangest of all. Adding the moon just in the middle of the circlet and close to a Carbon star was a very nice bonus. I'll keep looking for this strange events.

You can browse all the photos from this conjunction here:


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