Moon and Star Conjunction

The waning Moon shone near the bright star Aldebaran in the dawn sky.

This was a beautiful sight this morning, before dawn on July 29. The crescent Moon, its night side illuminated by Earthshine, shone just below the brightest star in Taurus.

We are currently in 3-year period when the Moon’s path is taking it near or in front of Aldebaran every month. However, most of these occultations or conjunctions are not well-timed for any particular location. And many involve the too-brilliant gibbous or full Moon.

But this morning the timing and Moon phase were perfect. From my longitude on Earth in Alberta, the Moon passed closest to the star just before the sky was getting too bright with dawn. Having them set against the deep blue twilight was perfect.

From farther east the Moon would not have appeared as close to Aldebaran as this before sunrise. From farther west the Moon and star would have appeared much lower in the sky at closest approach.

Moon & Aldebaran Screen


For this image I shot 6 exposures, from 2 seconds for the Earthshine, twilight sky colour and stars, to 1/125th second for the bright crescent. I then stacked, aligned, and blended them together using luminosity masks – masks that hide or reveal parts of the image based on the brightness of the scene. You can see them in the Photoshop screen shot – Click on the image to enlarge it.

How do you create these masks?

• Turn off all the layers except the one you want to create a mask for.

• Go to Channels and Command/Control Click on the RGB Channel.

• That automatically selects all the highlights.

• Go back to the image layer and then hit the Add Mask button down at the bottom of the Layers panel (the rectangle with the black dot in it).

• Done. Repeat that for each image layer.

More traditional high dynamic range or “HDR” stacking left odd colour fringing artifacts and double images on the slowly moving Moon, despite applying what is called “de-ghosting” and despite using a mount tracking at the lunar rate. I tried merging the images with HDR, but it didn’t work.

A nifty Photoshop action from the Astronomy Tools set by Noel Carboni added the diffraction spikes.

I shot all images with the 130mm Astro-Physics refractor at f/6 and the Canon 60Da camera at ISO 400.

— Alan, July 29, 2016 / © 2016 Alan Dyer /

2 comments on “Moon and Star Conjunction”

  1. Sky conditions were too cloudy in Halifax to view this event. During daytime, the Moon would have passed in front of Aldebaran! It would have been viewable in a telescope. 😦

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