Jun 3, 1999

Now you see it, now you don't



Now you see it, now
you don't


Amateur astronomers around North America captured beautiful images of a lunar occultation on May 21, 1999
Credit and Copyright: Jerry Winkler
June 3, 1999: On May 21, 1999 the Moon passed in front of the bright star Regulus, offering North Americans a rare opportunity to view the eclipse of a distant star without a telescope. Astronomers were hopeful that thousands of people would not only watch the unusual spectacle, but also record it using their camcorders. Video tapes of bright star occultations can be used to make precise topographical maps of the Moon's limb which, in turn, help scientists use solar eclipses to monitor the constancy of the sun's diameter and its long-term energy output.

Above: This of Regulus disappearing behind the Moon's darkened limb on May 21, 1999 consists of twenty-eight 2 second video frames. The video was obtained in Houston TX by Mr. Jerry Winkler using an ASTROVID 2000 video camera at the prime focus of an 80 mm Celestron refracting telescope (910 mm focal length). Regulus is a bright dot on the lower left hand corner of the image. It disappears abruptly about half way through the animation loop. A is also available. The AVI version features higher resolution images at a 1 second frame rate. Image Credit: J Winkler, Copyright 1999, all rights reserved.

"This was probably the most videorecorded occultation to date," says Dave Dunham, president of the International Occultation Timing Association which issued a call for amateur videos of the eclipse. "I asked everyone who recorded the occultation to send me a message, and so far 40 or 50 have replied. We'll be analyzing the tapes in the coming months as they arrive."


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Located just a few miles from the Johnson Space Center, Mr. Jerry Winkler, a Science@NASA reader, captured some beautiful images during the occultation.

"The moon was a little larger than my TV screen so I put Regulus in the lower left hand corner and part of the moon in the upper right," explained Winkler. "The extinction of Regulus occurred sharply at 4:31:40 UT in Houston."

Although the occultation was widely touted as a "naked-eye" event, the bright glare of the waxing quarter Moon nearly overwhelmed the weaker glow from Regulus and made the eclipse difficult to see without binoculars or a camcorder with sufficient magnification. A sharped-eyed observer far from city lights might have been able to glimpse the disappearance of Regulus behind the moon's darkened limb, but its reappearance from behind the sunlit hemisphere was impossible to see without a telescope.
click for animation!
Left: This image shows Regulus emerging from the sunlit limb of the moon just after 5:25:30 UT on May 21, 1999. An of the reappearance was contructed from twenty-four 2 second video frames obtained by Mr. Jerry Winkler in Houston TX. Regulus is a 1st magnitude blue-white star, about three times as massive as our sun, located 85 light-years away. Although it is very bright, Regulus is far away and much dimmer than the brightly-lit Moon as seen from Earth. The reappearance of Regulus could only be seen through binoculars or a telescope. A is also available. The AVI version features higher resolution images at a 1 second frame rate. Image Credits: J Winkler, Copyright 1999, all rights reserved.


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If you enjoyed the eclipse of Regulus and would like to see another, you may be able to view an occultation of Aldebaran, a bright star in Taurus, later this year. The northeastern U.S.A. and eastern Canada will have two chances to see the moon eclipse Aldebaran, once early in the morning of July 10th and again late in the evening of September 29th. Of the two, July 10 is likely to be best date for naked-eye observers. The Moon will be a slender, waning crescent on July 10, 1999 and its light will not overwhelm 0.8th magnitude Aldebaran so badly as the half moon dominated Regulus on May 21. For more information about the upcoming July occultation, please visit the IOTA web site.

The author wishes to thank Jerry Winkler (Houston, TX), Joe Toledo (San Jose, CA), and Don Newberry (Loxley, AL) who contributed research quality videos of the Regulus occultation to Science@NASA.


Web Links


International Occultation Timing Association -- learn more about lunar occultations

The Moon occults Regulus -- from Sky & Telescope

Moon Occults Saturn -- Astronomy Picture of the Day, May 8, 1999

Help Map the Moon -- Astronomy Picture of the Day, Sep. 11, 1998

Occultations and rising moons -- Astronomy Picture of the Day, May 13, 1998

X-ray Moon and X-ray Star -- Astronomy Picture of the Day, Feb. 27, 1996

Sunshine, Earthshine at the Lunar Limb -- Astronomy Picture of the Day, May 30, 1996

The sky on Friday May 21, 1999 -- from

The Nine Planets: the Moon -- from SEDS

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Author: Dr. Tony Phillips
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