Printer Friendly

Observing through a truly large telescope: the author and friends enjoyed a memorable night of observing through what was once the world's largest telescope.

When it comes to visual observing, what constitutes a truly large telescope? Over the years I've observed through various instruments that meet any reasonable definition of that criterion. I looked through a friend's 32-inch relay scope (S&T: May 2011, p. 32). At star parties I've gazed at galaxies, clusters, and nebulae through apertures of 40 inches and more. And in 2002 I had the privilege of observing through the Mount Wilson 60-inch reflector, an unforgettable session I described in my Spectrum column (S&T: Nov. 2008, p. 8).

But when it comes to sheer size, nothing will ever top my experience on the night of November 4-5, 2015. Together with five friends from the Astronomical Society of Harrisburg, PA (ASH), I observed 20 objects through the Mount Wilson 100-inch Hooker Telescope, which was the world's largest from 1917 to 1949, the year the 200-inch Hale Telescope on Palomar Mountain saw first light. Edwin Hubble used the 100-inch in the early 1920s to prove that M31 and other spiral nebulae were in fact separate island universes, and later that decade, working on the 100-inch with Milton Humason, he discovered the expansion of the universe.

The great news is that any observer or club can sign up for a night on the 100-inch, for a price. Even though my fellow ASH members and I were not treated to Mount Wilson's legendary subarcsecond seeing, it was still a thrilling experience, and there's a good chance you'd enjoy even better views.

Hallowed Ground

The 60- and 100-inch reflectors were erected on Mount Wilson after astronomers recognized its outstanding seeing conditions, made possible by the laminar airflow over the 5,700-foot summit. With the large aperture and excellent seeing, the 100-inch telescope remained a research powerhouse for decades. Besides Hubble's great discoveries, astronomers used it to perform much of the spectroscopy required to classify stars and understand their evolution. Without question, the 100-inch is one of the most productive instruments in the history of science, and by proving the value of large reflectors, it paved the way for much larger telescopes.

When the 60- and 100-inch reflectors were built under the direction of George Ellery Hale in the early 1900s, Los Angeles was small enough that its light pollution didn't pose a significant threat. But the metro area has since expanded to 18 million people, who emit a vast amount of artificial light that creates a bright sky background over Mount Wilson. Typical moonless nights have a limiting visual magnitude of about 5. As a result, the glory days of the 100-inch have long since passed. It was last used for research in 2012.

The director of the observatory at that time, Harold McAlister, realized that the 100-inch needed a new purpose. For that, he looked to the public observing program on the 60-inch, which had started in the 1990s. "The great success of the 60-inch public access program inspired me to want to replicate that on the 100-inch as a means for producing an important new income stream for the Mount Wilson Institute," says McAlister.

But modifications were necessary before public observing could begin on the mountain. The 100-inch telescope was built during the era when photographic plates and spectrographs had taken over scientific research, so it wasn't constructed with the visual observer in mind. The telescope's Cassegrain focus rests 15 feet above the observing floor when the telescope points to the zenith, a significant safety concern for public observing in the dark.

To solve this problem, McAlister asked his Georgia State University colleague Laszlo Sturmann to develop an optical system that would let the public observe from a more accessible location. Sturmann finished the design in early 2012, and by September of that year his relay system had seen first light. Meanwhile, Dave Jurasevich, then Mount Wilson Superintendent, coordinated efforts to improve the telescope's pointing and tracking. The first public observing sessions commenced in 2013, and the program in its current form started in the spring of 2015.

In Sturmann's relay system, the light from the 100-inch telescope reflects off a 6-inch flat mirror before the Cassegrain focus. The light next goes "backward" through a Meade 152ED f/9 apochromatic refractor, which acts like a 1,368-mm eyepiece and recollimates the beam. The light is then brought to new focus by a 5-inch Explore Scientific refractor. As Sturmann says, "This is a very simple system, and the beauty of it is that both the Meade objective and the Explore Scientific refractor are used as they were intended, therefore the relay system itself has excellent image quality. It doesn't degrade the 100-inch telescope."

The relay system changed the original Cassegrain's focal ratio from f/16 to f/11.25 and made it possible to observe from a short ladder. The Explore Scientific refractor accommodates standard 2-inch eyepieces.

The Road to Mount Wilson

Ever since my 2002 observing session on the 60-inch, I've wondered what some of my favorite objects would look like if I could view them through this grand old reflector. So it was with particular good fortune that my longtime friend Bob Young informed me that he and a small group of ASH members were planning an observing night on the 100-inch. Bob is a retired planetarium educator with the State Museum of Pennsylvania in Harrisburg, and he served as president of the Astronomical League from 1978 to 1980.

Using the Mount Wilson Observatory's website (, Bob reserved a half night on November 2, 2015, for a fee of $2,700 (a full night goes for $5,000). Bob kept the invitation list small so each person could enjoy ample time at the eyepiece. Besides Bob and me, the other ASH members who flew to Southern California (and split the cost) were Jim Davis, Tony Donnangelo, Bob Hoover, and Roxanne Kamin.

Though we'd planned to observe that Monday night, Shelley Bonus, our contact at the Mount Wilson Institute, called on both Monday and Tuesday mornings with bad news: a weather front in the area meant it was very likely we'd be clouded out and so we shouldn't bother to drive up the mountain. Fortunately, there's plenty to do in the L.A. metro area, so we spent the daylight hours on Monday and Tuesday touring Griffith Observatory, the California Science Center, and Warner Brothers Studios.

All of us had arranged to stay in the area a few extra days, so when Shelley called Bob with good weather news on Wednesday morning, we were ready to go. After lunch we visited a grocery store in La Canada Flintridge to pick up food for dinner, then drove for about an hour up winding roads that offered picturesque views of the San Gabriel Mountains. After stopping at several overlooks to take photos, we arrived at the observatory's lower parking lot around 2:45 p.m. Fifteen minutes later Gale Gant of the Mount Wilson Institute met our group and gave us a highly informative 3-hour tour of the observatory, which included visits inside the 60- and 100-inch domes. Among the many highlights was seeing Edwin Hubble's storage locker, with his name still affixed to the front.

Twenty Targets

I had seen the 100-inch telescope on two prior visits, but walking into the dome and gazing at this magnificent instrument is an experience that never gets old. The scope and its surroundings exude history and wonder in a way that can only be appreciated in person. As Tony puts it, "I walked into the dome, and my jaw dropped. It was speechless exhilaration. We were going to observe through this historic behemoth!"

Gale concluded the tour by introducing us to our three assistants, who are contractors for the Mount Wilson Institute: telescope operator Jeff Schroeder and session directors Norm Vargas and Tom Mason. I can't speak highly enough of their friendliness, knowledge, and efficiency. Jeff slewed the telescope from a console one level above the observing floor. Norm was stationed at the eyepiece and let Jeffknow when our target was in view. Norm and Tom provided expert commentary throughout the evening, and for the most part, our ASH group let them select the targets.

It usually took Jeff several minutes to slew from one object to the next. We were immediately struck by the quiet movement of the 100-ton yoke mount. The relay system was beautifully constructed for eyeball-to-eyepiece observing. When the telescope was aimed near the zenith, all I had to do was stand straight up and the eyepiece was at eye level. Even when the scope was aimed relatively low, we only needed to climb a few steps up a ladder to view our target.

My fellow ASH members brought several of their own eyepieces, but we mostly used the observatory's Tele Vue 55-mm Plossl, which yields a magnification of 520x and a true field of view about 5.5 arcminutes across.

We ended up observing 20 objects under clear skies starting at 6:10 p.m. Based on double-star observations, the three assistants estimated that the seeing ranged from 1 to 1.5 arcseconds, good in many circumstances but mediocre for Mount Wilson. Each of us spent several minutes soaking in individual targets--sufficient time for me to develop a good idea of how the view compared to what I've seen in various amateur scopes under different sky conditions. After I observed an object, I dashed across the room to jot down my impressions on a notepad under a red light. Here are my notes for each object, in order and edited for clarity and brevity:

[1] Epsilon (e) Lyrae (the Double Double)--We observed this object first to check seeing conditions. The scope easily split both doubles, but all four stars were swimming with halos around them. Not as bright as I expected it to be.

[2] M57 (Ring Nebula)--Very diffuse, not great surface brightness. Fleeting glimpses of the central star with averted vision. Gauzy central region. Bob Young: "I didn't notice any color other than the usual green." Roxanne: "Central green along with red outer ring colors."

[3] Beta ([beta]) Cygni (double star Albireo)--This is the brightest I've ever seen the two stars in an eyepiece; the famous gold and blue colors are impressive. But the stars are fuzzy due to poor seeing; I couldn't bring them to a sharp focus. Bob Young: "Like two searchlights in your face." Jim: "Like two bright balls of flame."

[4] NCC 7009 (Saturn Nebula, planetary nebula in Aquarius)--Target suggested by Jim. The blue-green color is very obvious, the brightest I've ever seen it. Hints of internal structure. The famous ansae seen in Hubble images are easily visible but not prominent. But the nebula clearly looks like its namesake planet, very impressive. No hint of a central star.

[5] Neptune--The characteristic blue hue is impressive, but the disk was a smudgy glow, not a sharp disk. Triton was continuously and easily visible at about 8:45 on a clock face. Norm Vargas: "We don't get excited unless the seeing is better than 1 arcsecond. That's why the telescope was built here."

[6] M2 (globular cluster in Aquarius)--It's a nice, but not spectacular, view. A smudgy, unresolved central concentration of stars. Looks like bright individual outer stars have been slingshot out of the central region in scattershot fashion. Stars fill the view.

[7] M15 (globular cluster in Pegasus)--Couldn't bring the stars into a sharp focus. The central concentration of stars is easily visible but indistinct. The outer stars were bright and impressive.

[8] NGC 7331 (spiral galaxy in Pegasus, brightest member of the Deer Lick galaxy group)--The main galaxy itself is quite bright, and three companions were easily visible at 6:30, 8:30, and 12:00 (the farthest) on a clock face. NGC 7331's nucleus is very easy, the rest of the disk looked tipped, like M31. Fairly symmetrical on right and left. Not much hint of spiral arms or dust lanes. Two other companions were visible but very difficult to see even with averted vision.

[9] NGC 7662 (Blue Snowball Nebula, planetary nebula in Andromeda)--My favorite object of the night so far. The blue color is "in your face." A bright inner shell is very prominent and easy to resolve against the faint outer shell, which is unaligned. No central star.

[10] NGC 7814 (spiral galaxy in Pegasus)--Unfortunately, I saw virtually nothing due to the light-polluted sky background.

[11] Uranus--Pale blue color easy to discern. But the planet is a blob rather than a resolved disk. One moon was two planet diameters away at 12:30, another about four diameters away at 5:00. Later, with guidance from Tony, I saw two additional moons, but they were very, very faint, in and out, at 6:00 and 8:00, and very close to the planet. Norm said that on a good night, one can easily see four or five moons.

[12] NGC 604 (H II star-forming region in the galaxy M33)--An indistinct, faint smudge about 1 arcminute across. No hint of the bright central star cluster seen in Hubble Space Telescope images. 1 see a few other bright spots in the field, but no hint of larger structure of M33 (the Triangulum Galaxy).

[13] M76 (Little Dumbbell, planetary nebula in Pegasus) --The little dumbbell shape was easy to discern, but was still very faint against a bright sky background. The right side of the right dumbbell was the brightest part.

[14] Gamma ([gamma]) Andromedae (double star)--Intense blue and gold colors. Stars look like little sparklers due to bad seeing. Still, the stars are easily split. Jeff Schroeder: "The scope has no hint of astigmatism, so the lack of sharpness is all due to the atmosphere."

[15] G1 (Mayall II, globular cluster in M31)--The cluster is the left "star" in an equilateral triangle. Brighter than the other two stars and less resolved. Roxanne inserted her 20-mm 100-degree Explore Scientific eyepiece she won at a star-party raffle, so it's seeing first light on a 100-inch scope! It spread out the triangle but otherwise there was no major difference.

[16] Core of M31--Detected a bright central spot just a few arcminutes across, surrounded by a semi-bright glowing region. The entire field looked brighter than the sky background. Averted vision reveals the barest hints of dust lanes on the opposite sides of the core.

[17] TX Piscium (carbon star)--This looks like an intense orange sparkler, not well focused. Jim commented that it seemed about as bright as Aldebaran in a normal scope to him. Roxanne: "an intense harvest orange color."

[18] M77 (barred spiral galaxy in Cetus)--The bright, cigar-shaped nucleus was well defined. It's a faint tipped galaxy, and I saw no suggestion of spiral arms or dust lanes. But others saw hints of spiral arms that looked like hooked appendages.

[19] NGC 1535 (Cleopatra's Eye, planetary nebula in Eridanus)--Norm: "I call it the Liz Taylor Nebula." Best object of the night so far, a true "Wow!" view. A very bright central star with a bright glowing ring around it that has a tinge of blue-green, like M57 through a 16-inch scope. Easily discernible outer glow. Looks like a glowing bull's eye with a central dot and two outer rings.

[20] Trapezium Region of M42--We saved the best for last. Four blazing bright stars, and two fainter Trapezium stars are easy to see, both reddish with the one on the right quite distinctly red. Tremendous detail in the mottling of the surrounding nebulosity, which has a noticeably bluish cast with a tinge of green. The most color I have ever seen in this region. We tried Roxanne's 20-mm eyepiece but couldn't bring the view into sharp focus because the higher power magnified the poor seeing. Jim: "Okay, that wins tonight."

Jeff and Norm shut things down at 12:45 a.m., when a third-quarter Moon was rising over the eastern horizon. Still giddy with excitement, we spent several minutes taking group photos under the giant reflector before heading outside for our drive back to Los Angeles.

Experience of a Lifetime

From a pure observing perspective, I've had better views of many of these objects through much smaller scopes operating under darker and steadier skies. I recall from my experience on the 60-inch that the seeing makes a world of difference. On that night we enjoyed subarcsecond seeing, and the high-magnification views of Jupiter and Saturn (both near opposition) were like looking at them up close through a spaceship portal.

The other factor, of course, is light pollution. The bright sky background partially washes out deep-sky objects with low surface brightness, and this effect was particularly noticeable with galaxies. The objects with high surface brightness, particularly the planetary nebulae and the Trapezium region, were showstoppers. Norm informed us that on some nights, a marine layer covers metro L.A., reducing light pollution.

Even though the relatively poor seeing degraded some of the views, this was one of my most thrilling astronomical adventures. The 100-inch brought out more nebula colors than I've ever seen. The combination of the exceptional views of several objects and just knowing I was looking through the same scope used by Hubble to discover the expanding universe made it a night never to forget. As Bob Young expressed as we were driving down the mountain, "It was an experience of a lifetime."

Word is just beginning to spread that the 100-inch is available for visual observing, so there are many open nights in the coming year. My ASH friends and I heartily recommend that you check it out. As Roxanne said at the end of the night, "Even if the seeing wasn't the greatest, the magic was still there."

To sum up, if you want to enjoy a beautiful night of observing at a historic observatory with a legendary (and giant!) instrument, all while supporting a venerable institution, check out the Mount Wilson Observatory website and sign up!

Robert Naeye was editor in chief of Sky & Telescope from 2008 to 2014. He joined the Astronomical Society of Harrisburg, PA in 1986, shortly after graduating from college and while he was living in nearby Hershey. He extends his gratitude to Bob Young for arranging the observing session.

Tips for Mount Wilson Visual Observers

Both telescopes are available from April through December. They're closed January through March for maintenance and because of frequent inclement weather.

The summer months have the best weather and seeing, but the nights are shorter, so you may feel pressed for time.

Weekend nights near new Moon are booked far in advance, but weeknights are usually open.

The maximum group size is 18 people for the 100-inch, and the maximum group size for the 60-inch is 25 people. I strongly recommend keeping your group relatively small so you won't spend too much time waiting in line.

At present, the fee is $950 for a half night and $1,700 for a full night with the 60-inch; the 100-inch is $2700 for half a night, $5000 for a full night of fun.

Ask for permission before bringing your own eyepieces.

Bring plenty of warm layers, especially if you go in the spring or fall. When we closed shop around 1:00 a.m. in November, the temperature inside the dome was barely above freezing.

If you get cold or hungry, you can go downstairs to a small room where you can warm up, eat a sandwich, or make a hot drink. Bring your own food and drink!

Don't show up in Los Angeles expecting the first night to have perfect weather. Build some flexibility into your schedule and travel plans in case you have to wait several nights for clear skies.


Please note: Some tables or figures were omitted from this article.
COPYRIGHT 2016 All rights reserved. This copyrighted material is duplicated by arrangement with Gale and may not be redistributed in any form without written permission from Sky & Telescope Media, LLC.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2016 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Title Annotation:Big Glass; Mount Wilson 100-inch Hooker Telescope
Author:Naeye, Robert
Publication:Sky & Telescope
Geographic Code:1USA
Date:Sep 1, 2016
Previous Article:Astronomy & big big data: how will astronomers cope with the tsunamis of raw data soon to pour in from wide-field surveys?
Next Article:Find your Dawes limit.

Terms of use | Privacy policy | Copyright © 2021 Farlex, Inc. | Feedback | For webmasters |