SERENDIPITY: CRESCENT MOON AND URANUS!

2015 February 21, 7:29 p.m. EST (Feb. 22, 00:29 UT)
Rosemary Hill Observatory • Bronson • Florida

Brief Object Notes: Uranus, "officially" discovered by William Hershel in 1781, moves in a solar orbit with a mean distance of 19 astronomical units. At this distance, the disk of Uranus is barely discernable in earth-bound telescopes, varying from about 3.3 to 4.0 arc seconds. However, under good seeing conditions, observer's should see this object not as a star but with a small, greenish disk.

The Occultation: At approximately 5:41 p.m. EST, Uranus began to pass behind the dark limb of the waxing, 3- day-old Crescent Moon over North Central Florida, a lunar occultation. (This phenomenon results from the Moon's eastward motion on the sky due to its orbital motion with Earth.) This event would not have been observable since sunset was not until 6:24 p.m. EST, or 43 minutes later. However, the bright limb reappearance at about 6:51 p.m. should have made this planet visible during deepening evening twilight.

The Photograph: Plans were made to image this scene beginning at seven o'clock when Uranus should have been about four arc minutes from the bright lunar limb. However, clouds and considerable haze in the western sky diffused the image of the Moon and scattered moonlight throughout the western sky making it difficult to image the Moon. About thirty minutes later, the sky became slightly less hazy but the sky around the Moon remained very bright. Still I took a few photos in desperation. I also forgot that by 7:30 p.m. EST Uranus would now be about 20 arc minutes from the Moon's limb. This would almost put Uranus out of the telescope's field of view if the Moon were centered.

Thus, photographs were taken under very hazy skies with poor seeing using my 5-in., f/5.2 refractor. Uranus was then 20.8 AUs from Earth (light time 2h53m!), with a disk only 3.9 arc seconds across, appearing at magnitude +5.9. Although faint, this could have made Uranus a naked-eye object under very dark, clear skies. (Still, quite a challenge!)

Serendipity: The next day, after reviewing photos taken at Rosemary Hill Observatory, I noticed four images of the Moon made when the Moon was very off-centered. Being curious, I carefully studied each and noticed one image, with a vastly overexposed Moon, seemed to show an object near the photo's edge. After some quick processing, Uranus dramatically popped out at precisely the position it should have been at the time of the photo was taken (approximately 19 arc minutes or 0.3 degrees from the bright lunar limb)!

In addition, I could make out the planet's small disk that also showed the greenish hue I knew characterized this distant body. See photo below.

If you cannot find Uranus, put cursor over image to locate this planet! A highly magnified image of Uranus will also appear. (The image of Uranus is very distorted from optical aberrations since its position is almost at the edge of the telescope's field of view.)

The photograph is highly processed to bring out Uranus. (This results in an over-processed lunar image and a strange sky background from scattered moonlight.) However, the planet is easily visible near the bottom left edge of the photograph.

PUT CURSOR OVER IMAGE TO IDENTIFY URANUS — ALSO CLICK IMAGE TO ENLARGE

Photo Details 2015 Feb. 21, 7:29 p.m. EST TeleVue 127 mm, f/5.2 APO Refractor, Foc. Len. 660 mm w/Televue 4x Powermate (Effec. Foc. Len. 2,640 mm) Camera: Canon DSLR EOS 5D II, Exposure 2 sec, f/21 (ISO 2500)

OBSERVATIONAL CHALLENGES Find Uranus (Sky Maps & Finding Charts Recommended) Is Uranus visible with the naked eye? With binoculars? Can you discern a disk with your telescope? What color does the planet appear If successful in finding/observing Uranus, try Neptune! (Neptune's disk is half as large and is more than 5x fainter at mag. +8.0) QUESTION: Astronomical Symbol for Uranus: (Sun & Mars symbols combined, spear pointing up) Represents heaven combining power of Sun and spear of Mars Early Version of Symbol: (Often still used in astrology) Can you describe what the old symbol represented? ANSWER HERE

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Images © 2004–2015 H.L. Cohen
Email Cohen followed by @astro.ufl.edu
Last updated 2015 May 18