Category Archives: Astronomers

Analemma, the Slender Figure Eight in the Sky


Myself 

By T. V. Antony Raj

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Definition of Analemma by Merriam-Webster: “A plot or graph of the position of the sun in the sky at a certain time of day (such as noon) at one locale measured throughout the year that has the shape of a figure 8; also : a scale (as on a globe or sundial) based on such a plot that shows the sun’s position for each day of the year or that allows local mean time to be determined.

Our Earth orbits around the Sun on an elliptical path. It also revolves around the Sun on a slant with an axial tilt of about 23.4 degrees. This leads to some interesting observational effects. One of these is the analemma, the apparent path traced by the Sun in the sky when observed at the same time of day over the course of a year.

Due to the Earth’s orbital eccentricity and its axial tilt, our Sun does not appear in the same position in the sky at the same time every day throughout the year. These two factors combine to generate the slender figure-eight, called analemma ( Greek “support”) curve.

So, the astronomers use this analemma diagram that shows the deviation of the Sun from its mean motion in the sky, as viewed from a fixed location on the Earth.

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Analemma on a globe (Source: analemma.com)

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The analemma diagram with the Sun’s path resembling a lopsided figure eight can often be found printed on globes of the Earth, usually somewhere over the Pacific Ocean where there is lots of room to print it.

The north–south component of the analemma is the Sun’s declination, and the east–west component is the equation of time. Most often, the diagrams of analemmas carry marks that show the position of the Sun at various closely spaced dates throughout the year. Analemmas with date marks are used for various practical purposes. Without date marks, they are of little use, except as decoration.

Earlier, prior to the 18th century, the term “analemma” referred to any tool or method used in the construction of sundials. Now, the term “analemma” is used in conjunction with sundials to convert between apparent and mean solar time.

Analemmas are photographed by keeping a camera at a fixed location and orientation and taking multiple exposures throughout the year, always at the same clock-time.

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Analemma posted by Giuseppe Donatiello

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The above image is a photo of an analemma posted by Giuseppe Donatiello.

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Analemma photo taken by Jack Fishburn in 1998–99.

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The above is an afternoon analemma photo taken in 1998–99 by Jack Fishburn in Murray Hill, New Jersey, USA. The Bell Laboratories building is in the foreground.

Although the term “analemma” is used to refer to the Earth’s solar analemma, it can be applied to other celestial bodies as well.

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Comet Hale-Bopp: The Most Widely Observed Comet of the 20th Century


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Myself By T.V. Antony Raj
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Image of comet Hale-BoppC/1995 O1 (Hale-Bopp), taken on 1997 April 04. The field shown is about 6.5° x 6.5°. At full resolution, the stars in the image appear slightly elongated, as the camera tracked the comet during the exposure. (Photo: E. Kolmhofer, H. Raab; Johannes-Kepler-Observatory, Linz, Austria)
Image of comet Hale-Bopp (C/1995 O1), taken on 1997 April 04. The field shown is about 6.5° x 6.5°. At full resolution, the stars in the image appear slightly elongated, as the camera tracked the comet during the exposure. (Photo: E. Kolmhofer, H. Raab; Johannes-Kepler-Observatory, Linz, Austria)

On July 23, 1995, two independent observers Alan Hale and Thomas Bopp in the United States discovered the comet Hale-Bopp. This comet formally designated C/1995 O1 was perhaps the most widely observed comet of the 20th century, the third largest comet in the last 500 years, and one of the brightest seen for many decades. It was visible to the naked eye for a record 18 months. The previous record holder, the Great Comet of 1811, officially designated C/1811 F1, was visible to the naked eye for around 260 days.

Dr. Alan Hale
Dr. Alan Hale

Astronomer Alan Hale was born in 1958 in Tachikawa, Japan, when his father was serving in the United States Air Force. Four months later his father got transferred to Holloman Air Force Base outside Alamogordo, New Mexico. Hale served in the United States Navy from 1976 to 1983. In 1980, he graduated from the U.S. Naval Academy. Next, he joined the Jet Propulsion Laboratory (JPL) and worked as an engineering contractor for the Deep Space Network until 1986. As a contractor, he worked in several projects involving spacecraft, including Voyager 2. After Voyager’s encounter with Uranus, he left JPL. He attended New Mexico State University in Las Cruces. In 1992, he earned his Ph.D. in astronomy.

Hale had spent hundreds of hours searching for comets without success. On July 23, 1995, while tracking known comets from his driveway in New Mexico he chanced on the comet co-named after him just after midnight. The comet with an apparent magnitude of 10.5 was near the globular cluster M70 in the constellation of Sagittarius. He checked and confirmed that there was no other deep-sky object near M70. Next, he consulted a directory of known comets and established that none of them was in that area of the sky he had observed. He then found the object moving relative to the background stars.

As a trained astronomer who had seen about 200 comets, Hale to register his finding sent an email to the Central Bureau for Astronomical Telegrams (CBAT) in Cambridge, Massachusetts, the clearing house for astronomical discoveries operating under the auspices of Commission 6 of the International Astronomical Union (IAU). A few hours later his effort was rewarded. His new comet was officially designated C/1995 O1. His name would also be attached.

But Alan Hale was not the only observer that night.

That very night, about 400 miles (644 kilometers) away, Thomas Bopp was observing star clusters and galaxies through telescopes with friends in the desert outside Phoenix, Arizona.

Thomas Bopp in 1997 (Photo: Ron Baalke)
Thomas Bopp in 1997 (Photo: Ron Baalke)

Amateur astronomer Thomas J. Bopp was born in 1949 in Denver, Colorado. Later he relocated with his family to Youngstown, Ohio, where he graduated from Chaney High School in 1967. He attended Youngstown State University in Youngstown, Ohio, and has lived in Tucson, Arizona since 1980. He is a Life member of the Mahoning Valley Astronomical Society (MVAS).

Bopp was a manager at a construction materials factory. He did not own a telescope. He too noticed some fuzzy object near M70 in the constellation of Sagittarius and pointed it out to his friend Jim Steven who owned the 70 inches telescope of Dubsoniano design he was using.

Bopp had never come across a comet. Jim looked at Bopp and said, “Tom, I think you have a comet.”

He knew he had to contact the Central Bureau for Astronomical Telegrams in Cambridge, but he did not have the address with him. So, he drove back home to get it.

In the wee hours he managed to send a Western Union telegram to the Central Bureau for Astronomical Telegrams in Cambridge where its arrival was greeted with bemusement. Brian Marsden, the leading voice on a committee that has the last say laughed. “Nobody sends telegrams anymore,” he commented. “I mean, by the time that telegram got here, Alan Hale had already e-mailed us three times with updated coördinates.”

However, the following morning, the comet was confirmed as a new entity and designated as C/1995 O1. The discovery was announced in International Astronomical Union circular 6187.

Sometimes weird things happened with when major comets appeared. According to a  report, 39 members of a California cult claimed they were departing on a spaceship that was trailing comet Hale-Bopp and ate their last meal before ritually committing mass suicide. For Thomas Bopp, the comet portended a loss. As comet Hale-Bopp reached its most spectacular point in the sky, his brother and sister-in-law who had been out photographing the comet were killed in a late night car crash. “This has been the best week of my life. And, the worst,” he lamented.

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