Mt Wilson photo tour and a brief observing report

Last night the PVAA had the 60-inch telescope booked at Mt Wilson. It had been ages since I’d been up there – my only other trips up were in 2009 and 2010 (observing reports here and here). So it was very satisfying to be back. It is amazing to look back and realize that in 2010 I was only 3 years into what has now been almost 9 years of stargazing.

The last two times I went up, we didn’t have time for a tour of the grounds, so about all I saw were the parking area, the 60-inch dome, and a few odds and ends in the distance. This time we got a nice long tour from Geo Somoza – most of the rest of this post is a photographic tour of part of the observatory. We didn’t have time to go through the museum up there, or see the solar telescopes – guess I’ll just have to go back again to catch those (which is no bad thing!).

I rode up with Ron Hoekwater, Laura Jaoui, and Gary Thompson, who kindly drove us. We left Claremont early and got up there about 6:00, well in advance of the planned 6:30 start time for the tour. While we were chatting outside the gate, we saw something ominous: a tower of smoke going up from the mountains to the west. This would come back to haunt us.

Here’s the dome of the 100-inch Hooker telescope – world’s largest from 1917, when it eclipsed the 60-inch telescope on the same mountain, until 1948, when it was eclipsed in turn by the 200-inch Hale telescope on Palomar Mountain. It is a bit staggering to realize that from 1908 to 1993, when Keck 1 went online on Mauna Kea, the three consecutive world’s largest fully-functional telescopes were all within 92 miles of each other in southern California. (The 240-inch Soviet BTA-6 saw first light in 1976, but it suffered terrible thermal stability and seeing problems and never performed anywhere near its full potential.)

This bridge is nicknamed “Einstein’s bridge” because Einstein paused here for a famous photograph during a visit to Mt Wilson in 1931 – see that historical photograph here.

Here’s the scope itself, the same machine that Edwin Hubble and Milton Humason – a former mule-driver who worked his way up to master observer – used to chart the expansion of the universe. I was scheduled to go up and observe with the 100-inch last year, but I got very sick the day before and couldn’t make it. So that is still on the bucket list.

A view into the back of the mirror cell of the 100-inch telescope. The green champagne-bottle glass of the primary mirror is clearly visible. If you click through to the full-size version you may be able to see bubbles in the glass. The 14-inch-thick mirror had to be made in three separate ‘pours’ of molten glass, and bubbles from the first two pours were trapped by the layer above. The people at Mt Wilson were so concerned about the bubbles interrupting the figure of the mirror that at first they refused to work with it, but St Grobain Glassworks was unable to pour a better one and eventually George Ellery Hale ordered his people to grind and polish this mirror, which turned out to be fine at the optical surface after all.

In the old days, to observe visually with the 100-inch you had to go down a narrow hallway to a tiny room where light from the scope was bounced to the Coude focus. That was pretty unsatisfying so a few years ago the telescope was modified for more intimate visual observing. Now the primary mirror at the bottom of the scope bounces the light to a secondary up in the upper cage, thence to a tertiary at mid-tube which directs the light out to a quaternary mirror in the diagonal housing at the top of the black tubular assembly on the left of the scope in the above photo, thence down to a quinary mirror at the bottom of the black tube, then into the white refractor that is pointing down and to the right. A diagonal sitting nearby can be placed into the refractor to put the eyepiece into a convenient orientation when the scope is tilted.

The control board of the 100-inch, with at least three separate control systems lined up right to left in order of age. Most interesting is the old table on the right with the clock and the two periscopes. The periscopes allowed the telescope operator to see the telescope’s setting circles. Nowadays, the scope is controlled by the computers on the left.

Excited amateur astronomers lingering outside the dome of the 100-inch. We got to walk around on the walkway you can see on the outside of the dome. The entire dome rotates, walkway included. It’s a fearsome engine indeed.

On the left is one of the six domes of the CHARA array, I believe still the world’s longest-baseline optical interferometer. It has enough resolving power to image the discs of nearby stars. On the right is the 60-inch dome.

Geo shows us the concrete pier used during the speed-of-light experiments in the 1920s. More on those in a sec.

For decades in the late 1800s and early 1900s, Albert Michelson conducted a series of experiments to measure the speed of light. In a series of famous tests in the 1920s – almost two decades after Michelson earned his Nobel Prize – a beam of light was bounced from this pier on Mt Wilson to a mirror on Lookout Mountain, one of the foothills of Mt San Antonio, better known to locals as Mt Baldy – the mountain at whose base I live. The concrete pier on Lookout Mountain is still there and it is apparently an easy hike. It’s on my to-do list.

Sunset over LA. On the left, the marine layer of fog is moving in over the city. On the right, a tower of smoke is going up from a wildfire near Calabasas, about 40 miles to the south and west of Mt Wilson, and spreading out over the LA basin. For a while the smoke was going southeast from the fire, and it looked like it might miss us. But by the time it was getting dark, the wind had shifted and was carrying the smoke directly toward the observatory.

As darkness fell, we trooped into the dome of the 60-inch telescope.

Here are the controls for the dome’s shutter, which has to be opened for the telescope to see out, and closed again to protect the telescope during the daytime and in inclement conditions. The three light bulbs on the upper left of the console are original Edison bulbs – they have been working without ever being replaced since 1907 or so.

Our telescope operator, Christopher Burns, checks something on one of the computers in the control center, while beyond him Geo stands by the mercury tank in which the 60-inch telescope floats. Don’t worry, it’s fully sealed now. In the old days, it was open, and mercury would sometimes splash on the floor as the telescope rotated.

Our first target was Jupiter. As usual, the photo completely fails to do justice to the naked-eye view. The seeing was imperfect and I think the smoke from the fire might already have been affecting the views. The north and south equatorial and temperate belts were visible, and the Great Red Spot was prominent, but I could see little detail beyond that. I have seen much better on other visits, and indeed in much smaller scopes (see for example the two previous Mt Wilson observing reports linked at the top of this post). But I won’t complain too much – part of the joy of observing with the 60-inch is in the process, not the outcome.

After Jupiter we moved on to the globular cluster M3, and then the Sombrero Galaxy, M104. M3 was already looking a bit dim – certainly not as bright as it appeared in Ron’s 25-inch scope from RTMC last weekend – and about this time the smell of smoke became pronounced in the dome. We had a hurried look at M104, but it was just a dim smudge of light and I couldn’t even make out the dust lane.

After M104 we had to shut down early to protect the telescope. If ash from the fire was allowed to fall on the mirrors, it would combine with moisture in the air to produce acids which would eat away the coatings. In the photo above, Geo is shining a laser up through the optical train to check for ash on the mirrors.

It was a bummer to have to shut down early, but we had an awesome tour and it was fun to observe again with the 60-inch, even if only briefly. Geo and Chris were great hosts and everyone had a good time. We’ll get to reschedule our night on the scope, since we only got about an hour and a half of observing in, so the club’s investment is protected. It’s a shame about Mars, though – we won’t have another opposition this close for some time, and the planet will be noticeably more distant, smaller, and dimmer by next month already. Still, into every observing career a little rain – or ash – must fall, and I’ve been extremely fortunate. Two eclipses (2012, 2014), a Venus transit, and a Mercury transit in the last four years, and not one of them clouded out. Mars will be back, and I’ll be ready.