Barlow Bob – The Etalon Demonstration

2011 - Northeast Astronomy Forum & Telescope Show (NEAF). April 16 & 17, 2011The following article has been provided by Barlow Bob, founder & organizer of the NEAF Solar Star Party and regional event host & lecturer.   You can read more about Barlow Bob and see some of his other articles at

The Etalon Demonstration - By Barlow Bob

For many years, amateur solar astronomy icon Alan Daroff has attended the solar observing at NEAF, the Northeast Astronomy Forum. He is the senior member of our NSSP NEAF Solar Star Party solar staff.

Using a prism spectroscope, he demonstrated how the parts of a modern hydrogen-alpha solar filter create a breathtaking image of the Sun. He placed the H-alpha Fabry – Pérot etalon, plus blocker and trimmer filter parts, in front of the spectroscope slit. When sunlight passes through these instruments, you observe the red H-alpha spectral line at 656.28 nanometers.

At NSSP, I use the Lhires Lite high resolution grating spectroscope to recreate Alan’s impressive demonstration.

The Lhires Lite spectroscope with one of the filters sitting on the gnomon

The Lhires Lite spectroscope with one of the filters sitting on the gnomon

The Lhires Lite spectroscope produces an unforgettable image of the solar spectra. This new product is manufactured by Shelyak Instruments, a French NEAF exhibitor. It was designed as a simple user-friendly educational resource to demonstrate spectroscopy. By moving a side lever, you can observe different parts of the spectrum through an eyepiece.

The instrument can be used to observe the bright emission spectra of street lights or Geisler spectrum tubes containing different elements in their gaseous state. The dark absorption spectra of the Sun can also be observed. You would have to use the more sophisticated Lhires III high resolution spectrograph to observe and image the absorption spectra of the other stars.

The Lhires Lite has a 1/2” round short metal rod attached to the top near the slit that passes light into the device. The rod is called a gnomon.  The gnomon is used to align the slit with the Sun to ensure that sunlight enters the spectroscope. To align a Lhires Lite spectroscope on a photographic tripod with the Sun, you move the spectroscope until the gnomon faces the Sun. Then you move the spectroscope until the gnomon’s shadow disappears and the sunlight is passing through the slit into the spectroscope.  When sunlight reflects off of the holographic grating, it is separated into the colors of the electromagnetic spectrum.

When you observe the spectra of an incandescent light bulb, you see a rainbow of colors, from red to violet. However, when you observe the solar spectra of sunlight, you see the same rainbow of colors, with hundreds of thin vertical dark lines covering every color. These dark lines are the Fraunhoffer absorption spectral lines of the solar spectra, created when elements in the stellar atmosphere absorb at specific wavelengths. These Fraunhoffer lines are the fingerprints of stars, used by astronomers to analyze the physical properties of stars and other celestial objects.

Instead of holding the parts of the H-alpha etalon parts in front of the spectroscope slit with my hand, I use a holder that I designed to position the filter parts over the slit. The holder consists of three parts. Each part is a 2 ½ X 7” rectangular shaped piece of Masonite. A four inch long notch slightly wider than the width of the gnomon notch is cut into the center of the left side of the holder. A hole is drilled into the right side, centered to hold the filter part in position over the spectroscope slit. The middle part has a hole, slightly larger than the diameter of a filter part.  The top and bottom parts have a hole, smaller than the middle part.

The middle holder part is placed over the bottom holder part. Blue painter’s masking tape is placed over the right and left edges. A filter is placed in the middle hole. The top holder part is placed over the middle holder part. Masking tape is placed over the right and left edges and folded over covering the three holder parts. When the three filter holder parts are held together, the filter will be securely held in place between the holder parts. This prevents damage to the filter.

When viewed through the Lhires Lite spectroscope, each filter shows a different image. The etalon shows a series of thin bright H-alpha red lines separated by thin black lines, similar to a picket fence.

The Fabry – Pérot etalon creates peaks and valleys of only the bright red Hydrogen – alpha electromagnetic wavelengths. This etalon consists of two pieces of flat glass separated by mica. The glass is spaced a specific and exacting distance apart. When light passes through the etalon, only the wavelengths of the red H-alpha spectral line that fits between the two glass surfaces pass through. When you observe red solar prominences through an H-alpha solar filter, you observe only the bright peaks of this red wavelength.

At the 2014 NSSP – NEAF Solar Star Party, I asked WAA President Larry Faltz to place his digital point-and-shoot camera over the spectroscope’s TeleVue 24 mm Panoptic eyepiece to record the image produced by three different filters through the Lhires Lite high resolution spectroscope.


Red peaks and black valleys of an H-alpha Etalon filter


Blue peaks and black valleys of a CaK Calcium Etalon filter.


An H-alpha blocker filter. This blocks the wavelengths of light above and below the dark Hydrogen-Alpha absorption spectra line.  This dark line is visible at the top of the red color.

The blocker and trimmer filter parts allow only the wavelength of the red H-alpha spectra line to pass, blocking the other lines. You see the dark Fraunhoffer absorption line with only thin lines of bright red color on either side of this dark line, or no color over large areas.

Please attend NEAF and experience this unique educational spectroscopy demonstration at NSSP.

For further information, please visit

How an etalon works

The Fabry-Pérot etalon consists of a transparent plate with two dielectrically-coated reflecting surfaces. It uses the principle of interference between the multiple reflections of light between the two reflecting surfaces to convert the uniform light output of the Sun to a series of peaks and troughs looking somewhat like a sinusoidal “picket fence,” as shown in the blue curve in the illustration (illustration not to scale). Constructive interference occurs if the transmitted beams are in phase, and results in a high-transmission peak. If the transmitted beams are out-of-phase, destructive interference occurs. This results in a transmission minimum.


Modern hydrogen alpha telescopes use blocker filters to eliminate the peaks outside of the desired 656.28 nm wavelength. Two etalons in tandem can narrow the width of the peak, increasing sharpness and contrast.


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Best And Brightest Asteroid Occultation Ever To Be Visible Across New York State

Below is the official press release by the International Occultation Timing Association (IOTA) on the upcoming occultation of Regulus by asteroid Erigone on March 20th. Please reference for more up to date information, they will have more to announce about efforts to monitor this occultation in the next week or two. Meantime, this is your one-month warning!

Public invited to help measure size and shape of distant asteroid
Media contact: Ted Blank,
Alternate contact: Steve Preston,

Just after 2:05 a.m. EDT on March 20, 2014, anyone with clear skies along a 70-mile-wide belt running diagonally from Long Island and New York City up through New York State into Canada may be able to see the bright star Regulus simply disappear from the sky for up to 14 seconds as an invisible asteroid glides silently in front of it.

A chance alignment of orbits is predicted to cause Regulus to “wink out” as the mammoth asteroidErigone passes directly between Earth and the star, temporarily blocking its light from reaching us (the asteroid itself remains in its normal orbit which never comes anywhere near Earth). Regulus (the star which will wink out) is in the constellation Leo the Lion and, as one of the brightest stars in the sky, is easy to find.

An event where an object in space blocks the light from a distant star is called an “occultation,” from the Latin word meaning “to conceal or hide.” The International Occultation Timing Association (IOTA), a group of volunteers, collects observations on about 200 asteroid occultations per year. However, this is the first time that such a dramatic and obvious occultation will be visible in such a heavily populated area without the need for any kind of optical aid like a telescope or binoculars.

What makes this asteroid event more notable is that the public is invited to assist scientists in recording the event to measure the size and shape of the asteroid. Just by using a video camcorder, a digital SLR camera with video capability, or just a smartphone or a stopwatch, anyone can contribute to the scientific study of the asteroid in question. “In addition to the opportunity to share in a moment of celestial drama, we hope to enlist thousands of ‘citizen-scientists’ to time this event, allowing us to document it more thoroughly than any other asteroid occultation in history” said Steve Preston, President of IOTA. “The more observers scattered across the path of the shadow who time the disappearance and reappearance of the star, the more accurately we can measure the asteroid’s size and shape.”

IOTA has created a “Frequently Asked Questions” page at Here, detailed information may be found on the recommended techniques that the public may use to record and time the event, as well as how to submit their observations for analysis after the event.

Although the asteroid will remain a safe 100 million miles from Earth, as it passes in front of the star its 70-mile-wide shadow will sweep from southeast to northwest across Nassau and Suffolk counties, all five boroughs of New York City and the Hudson River Valley, with the center of the predicted shadow path following a line roughly connecting New York City, White Plains, Newburgh, Oneonta, Rome and Pulaski before crossing into Canada. See Illustration 1 for the current prediction of where the shadow will pass.



Ill. 1. Estimated path of the shadow of the asteroid Erigone during the occultation of Regulus on March 20, 2014. The green line represents the predicted center line of the ~50 mile wide asteroid shadow. The blue lines represent the width of the asteroid, where edges of the shadow would fall if the actual center of the shadow followed the green line. The red lines represent the uncertainty in the path, meaning that the actual shadow will most likely pass somewhere between the red lines. There is a smaller chance that one edge could be slightly outside one or the other of the red lines.

At the time of the occultation, Regulus will be about 40 degrees high in the southwest, or about half-way up from the horizon to a point straight overhead. Illustration 2 below is a “sky-map” showing the star’s location in the sky along with some convenient reference points to help get oriented.



Ill. 2. Finder chart for March 20, 2014, looking southwest. The red dot at the top represents the point directly overhead. Regulus will be approximately half-way up in the sky, at the bottom of the reversed “question mark” that makes up the “mane” of Leo the Lion. Saturn, the Moon, Mars and Jupiter are shown on this map in the positions they will occupy on this date, as are the twin stars of Gemini (Castor and Pollux) just above Jupiter.

To choose an observing location, members of the public can refer to Illustration 1 and select any place between the outer lines. Since the path the shadow will follow may change slightly, observers should check the online zoomable map at in the days before the event for any last-minute adjustments to the path prediction. Additionally, people situated as far as 10 path-widths on either side of the center line are encouraged to make an observation in case Erigone has a moon which might momentarily block the star’s light. Video recordings will be needed to confirm the fleeting disappearance that a tiny moon of Erigone might cause.

After the event, the public may report their timing observations, including reports of a “miss,” or no occultation. “Both actual timings and ‘miss’ observations are extremely valuable,” said Preston. “Timings of the disappearance measure the asteroid’s diameter in the dimension along its orbital path, but ‘miss’ observations improve our understanding of how wide it is across its path. Furthermore, both types of reports improve our understanding of the asteroid’s orbit.”

Typically only a few observers see these types of events, allowing the diameter of the asteroid to be measured at just a few places. However, with a large number of observers, the opportunity exists to categorize the asteroid’s entire silhouette, as seen for asteroid (234) Barbara in Illustration 3 below.



Ill. 3. Outline of asteroid (234) Barbara obtained by multiple observers timing an occultation in 2009. The observers were spread out across an area over 40 miles wide. The horizontal white gaps in the solid lines represent the period of time when the asteroid blocked the light from the star for that observer. The gaps between the lines themselves represent the distance between observers on the ground. Each observer saw the star pass behind a slightly different portion of the asteroid, allowing the asteroid’s diameter to be measured at multiple locations. Note the large crater at the south end of the asteroid. This level of resolution is far greater than anything possible with ground-based telescopes, but more observers would have allowed even finer details to be measured.

Members of the public with additional questions should refer to the FAQ page, email or see the article in the March, 2014 issue of Sky and Telescope Magazine.

About IOTA

The International Occultation Timing Association, with its worldwide sister organizations in Europe, the United Kingdom, Australia/New Zealand, Japan, S. Asia/India, Mexico, Latin America and South Africa, provides free occultation predictions and planning and analysis software, sponsors online Internet discussion groups and publishes the Journal of Occultation Astronomy. The main IOTA webpage is The Yahoo discussion group can be found at and is open to all with an interest in this topic.

A PDF copy of an article from the March, 2014 issue of Sky and Telescope Magazine on the occultation is linked HERE. Permission to include this article has been granted by Sky and Telescope.

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The Pizza Hut Universe – By Barlow Bob

2011 - Northeast Astronomy Forum & Telescope Show (NEAF). April 16 & 17, 2011The following article has been provided by Barlow Bob, founder & organizer of the NEAF Solar Star Party and regional event host & lecturer.   You can read more about Barlow Bob and see some of his other articles at

The Pizza Hut Universe - By Barlow Bob

You may have noticed that you see more stars in the night sky, during Summer and Winter. However, you see fewer stars in Spring and Fall. Why does this occur?

Think of our Milky Way galaxy as a giant pepperoni pizza.

In the night sky, of Summer and Winter, you are looking across our galaxy, in the direction of the next arm, of our galaxy, containing many stars. In the night sky, of Spring and Fall, you are looking through the top or bottom of our galaxy, containing fewer stars.

Laminate a picture of a pepperoni pizza, back to back, with a picture of galaxy M33. This galaxy looks like a pinwheel. Place these laminated pictures in a pizza box. Laminate a picture of a pizza store, back to back, with this story of The Pizza Hut Universe.

The pepperoni represents our solar system..
The pizza represents our galaxy.
The pizza box represents our local galaxy group.
The pizza store represents the universe.

©2000 Barlow Bob

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2013 Kopernik AstroFest

The 2013 Kopernik AstroFest has passed, and what a great event that was held.  We appreciate all of the support from amateur astronomers and public who attended, the KAS and Kopernik volunteers who made it happen, the great speakers who presented, and to the vendors who donated raffle prizes and other support.

While the weather wouldn’t help us out this year with respect to night time observing, the event provided attendees the opportunity for great collaboration, amazing speakers presented on a wide range of topics, and The Kopernik AstroFest Solar Star Party allowed for a few hours of solar observing.

Check out our Photo Gallery of the Kopernik AstroFest 2013 Event

Kopernik AstroFest 2013 Gallery


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AstroFest 2013 Press Write-Up

This article was originally published in the Press & Sun Bulletin

Kopernik to Host
ASTROFEST 2013 This Weekend

Kopernik’s AstroFest is a celebration of the night sky and amateur astronomy. In its 31st year, the three day event, running from Friday, October 4th to Sunday, October 6th, is held annually at the Kopernik Observatory & Science Center (KOSC) in Vestal, NY. Both KOSC and the Kopernik Astronomical Society (KAS) sponsor the event.

kop_teleAstroFest includes internationally recognized speakers on a variety of topics, exhibits, demonstrations, an amateur astronomy roundtable discussion, the Kopernik AstroFest Solar Star Party, children’s activities and workshops, and nightly observing session if skies are clear. AstroFest 2013 will also feature its popular raffle with prizes that include two high quality telescopes, two pairs of binoculars, a variety of astronomy gear, gift cards and an assortment of other raffle prizes and baskets.

One of the talks will be a discussion of Comet ISON which should be visible in November 2013 as it passes near the Sun.  This comet may undergo brightening that may make it an early morning, naked eye site to see.  It has the possibility of being a comet of a lifetime.

Astronomy Magazine’s columnist and astronomy book author, Bob Berman will discuss how colors and light in the universe can reveal information about these objects in the universe including what they are made of and where they came from.  Also, there will be an SKYPE interview with Dr. Carolyn Porco, who is best known as the leader of the imaging science team on the Cassini mission presently in orbit around Saturn. She also participated in planning the iconic 1990 “Portrait of the Planets” taken with the Voyager 1 spacecraft, which included the famous Pale Blue Dot image of Earth.  Dr. Porco is a fascinating science personality and an intriguing speaker.

As part of Kopernik AstroFest, our annual Star Party will be held in the main yard on clear sky evenings.  Anyone with a telescope is encouraged to set it up for observing, and then they can share their views of deep sky objects with other enthusiasts including public participants.  Observing will be held throughout the night into the early morning hours weather permitting.

In addition to nighttime viewing, on Saturday, Kopernik’s telescopes will be focused on the closest star to us, the Sun.   Joining in Kopernik’s solar observing will be the “Godfather of Solar Astronomy” Barlow Bob.  He will bring a selection of his vast array of solar telescopes for observing the Sun.  Come see the Sun in ways you have never seen before.

Kopernik AstroFest is a celebration of the universe that surrounds us, its beauty, and its mysteries.  It’s KOSC’s and the

domes2KAS’s pleasure to host amateur astronomers, people interested in astronomy and families with children of all ages.  Admission is $5.00 per day for all adults, and children under 16 are free with a parent.  Doors open at 3:00 PM on Friday afternoon, and at 8:30 AM on both Saturday and Sunday.

On clear evenings you will be able to observe Uranus, Neptune, double stars, star clusters, galaxies and other deep-sky celestial objects through Kopernik’s powerful telescopes. Also, for those adventurous early morning, pre-dawn sky watchers, we will attempt to locate the faint Comet ISON as a prelude to its winter show.  Saturn and Venus may also be visible during pre-twilight hours before dusk.  For more information on AstroFest 2013, an hourly schedule, activities, speakers and exhibits, please visit

For information regarding Kopernik Observatory & Science Center’s Fall classes, membership and other educational and outreach programs, please call KOSC at (607) 748-3685 or visit our website at


Patrick Manley is the Chairman of Kopernik AstroFest 2013

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AstroFest 2013 Preview

Here’s a quick AstroFest 2013 preview with Roy Williams with the local News Channel 12.

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