Occultation | Hidden In Broad Daylight

The word occult means different things to various groups. To me, it does not mean supernatural or magical, secret or mysterious, or beyond comprehension. As an amateur astronomer, it means to be hidden from view. For an hour this morning, the Moon passed in front of, and occulted from view, the bright star Aldebaran. The star Aldebaran is the eye of Taurus the Bull, northwest of the constellation Orion.

The Moon occults a lot of stars as it orbits through the heavens. It last occulted Aldebaran on September 4 of this year. What made the occultation today unusual is that it took place in broad daylight just before 9 am CDT. That made it a challenge to see since we don’t think of stars as daytime objects. We in the midwest have been enjoying clear transparent skies the past few days. I set up the telescope for the event. The Moon was high in the blue western sky. My small camera was readied to photograph the occultation through the eyepiece.

I could easily see Aldebaran by eye through the telescope. It was about 3 minutes before occultation. I brought the camera to the eyepiece. This first photograph did not use the zoom on the camera. It was in focus.

2015_1002MoonAldebOcc1

I zoomed the camera a little to enlarge the Moon. That improved the view. Later, I cropped and enhanced the image to get this view. No doubt the star was visible.

2015_1002MoonAldebOcc2

I waited and watched through the eyepiece to see the moment light from Aldebaran disappeared. That was very cool to see. It didn’t gradually dim. It was suddenly gone.

I set the timer for an hour. It would take the Moon that long to travel in orbit and allow light from Aldebaran to reappear on the other side of the orb. It did so right on time. It is a little hard to see in the crosshairs. Click to embiggen.

2015_1002MoonAldebOcc3

This was fun to witness. Clear skies and good optics helped make it work. I hope you enjoyed it.

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14 thoughts on “Occultation | Hidden In Broad Daylight

  1. One of the more interesting parts of my naval career was as navigator of the heavy cruiser, USS Saint Paul (CA-73). This was in 1969-70 and we didn’t have GPS, we used celestial navigation when out of visual or radar range of land. On clear days, several times, I was able to get a line of position from the moon in daytime. Crossed with a sun line, it fixed our location nicely. A moon line is a little trickier than a sun line because the moon’s relative motion makes timing more critical. Some stars were visible in the daytime, as in your example, but a sextant’s telescope is too weak to make those practical. Stars and planets are shot at twilight.

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      • Indeed. I read Sobel’s book, a very good one about how longitude requires precise time and how that was achieved. In those days and for just that reason every ship in the U.S. Navy carried three chronometers which were compared daily with radio time and with each other, noting their error rates. I would assume they still do – tradition hangs on in the Navy. The other essentials were the nautical almanac, updated yearly, and longitude tables for interpolating at different latitudes. A stronger telescope for the sextant would be advantageous except that it proves impractical because it is hand-held due to ship’s motion.

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  2. I’m assuming the significance of Aldebaran is that it’s bright enough for us to see it. As the moon moves around the earth, it temporarily lies between us and zillions of stars, but almost all of them are too faint for us to see even when they’re not blocked by the moon.

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  3. Fantastic work, Jim. And your occultation reminds me of oculus, which reminds me of another kind of art: James Turrell’s Skyspace at the Crystal Bridges Museum of American Art. I wasn’t able to experience it when I was there, but I’m hoping for a return trip in spring, and will arrange my schedule differently so that I can.

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