Neptune Conjunction

I love planetary conjunctions and watching the Solar System in action as the planets follow their orbits across the sky. I learned a long time ago that following planets regularly in the sky and watching their constant movements and relative sizes provides a deeper sense of understanding of our cosmic neighbourhood.

So it was frustrating to miss the unusually close conjunction (on the evening of 1st January 2017) of Neptune and Mars – due to eight days of thick cloud here in SW Sydney. The apparent separation between them that night was a mere five arc-minutes – and would have made a fine view in my telescope.


However, I didn’t get a viewing opportunity until five days later, when the gap between the pair had widened to 3.75°. This was much larger than the field of view in my telescope, so I made my first ever attempt to image Neptune with a camera on a tripod – and this was the result:

2017-01-06: Venus, Neptune, Hydor, Mars – with identifying text. (100mm focal length, 3.2 sec, f/2.8, ISO 2000, FOV about 12×8 degrees).
2017-01-06: Venus, Neptune Hydor & Mars. (100mm focal length, 3.2 sec, f/2.8, ISO 2000).
2017-01-06 Mars, Hydor & Neptune – with identifying text. (157mm focal length, 3.2 sec, f/2.8, ISO 2500, FOV about 7×5 degrees).
2017-01-06: Mars, Hydor & Neptune. (157mm focal length, 3.2 sec, f/2.8, ISO 2500).

Hydor is also known as Lambda Aquarii, a magnitude +3.75 star. Distance 390 light years.

Venus was magnitude -4.4, distance 0.73 AU.

Mars was magnitude +0.9, distance 1.68 AU

Neptune was magnitude +7.9, distance 30.52 AU

One light year = 63,241 AU.

The faintest stars in these shots were about magnitude +9.5

All images © R.Powell


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