Observatory Still Closed

The Palomar Observatory is still closed to the public and it expected to be closed for the coming weekend. The on-going engineering work taking place on the 200-inch Hale Telescope has prevented the crew from plowing the public parking lot. At this point we do not have an estimated date for our re-opening.

Friday Sunrise

Dual Exhaust Dome

If you have ever been on a tour of the Hale Telescope in winter, you know that the temperature inside the dome is cold. We keep the inside temperature at nighttime temperature all year long. As the seasons change and the weather systems come and go, the temperature inside the dome varies with them.

Heating the dome just doesn't make sense from an energy standpoint when you realize that almost every night the dome is opened and all the hot air would escape.


Astronomically, it is actually worse than that. While having a warm dome would be nice for visitors enjoying a tour and a work crew performing maintenance it would force all of the telescope's parts to adjust daily back and forth from warm in the daytime to that night's much colder temperature. This can take a significant amount of time when the temperature variation is large. During a period of adjustment it would be difficult to use our large telescope and have any useful results.

The temperature equalization of the telescope is one problem. The other is convection. Hot air rises. Heating the inside of the dome and then opening the shutters would essentially force warm air to rise right in front of the telescope. The result would be hopelessly blurry images much like you see when looking down a roadway on a warm summer day.

Last November during an interview for a TV documentary lights were set up to aid in the filming. The lights were both bright and hot. One of the lights was shining toward another one which happened to be close to the inside of the dome. The result is that the hot, rising turbulent air actually became visible as its shadow was cast on the inside of the dome.

Here is a short video clip showing turbulence caused by warm rising air inside our big dome.

Look just above the shadow of the light fixture to see the effect of the warm rising air.

That's exactly what you don't want for astronomy. Of course the interview was held many hours before that night's observing and didn't impact operations much at all because a couple of lights doesn't really change the overall temperature inside the dome.

One in a while it is actually a good thing to heat the inside of the dome.

Right now we are just a few days into an engineering run where the Palomar day crew and support engineers from Caltech will be disassembling the Hale Telescope's mirror supports. Each of the 35 mirror supports to be worked on during the next several weeks contains over 1,000 parts. Many of the parts are tiny and difficult to manage.

For this engineering run, since we will not be performing astronomical observations with the telescope, we will make an exception to the no heat in the dome rule. The heat is on.

Yesterday morning we hooked up two big electric heaters, one of which is seen below.


We also recently modified the dome so that we could run two big propane heaters to heat the interior for the crew. So to safely vent away the exhaust gasses two dual exhaust vents were added. Have a look for them the next time you are visiting the observatory.

The temperature inside the dome has climbed all the way up to 40F, making it not quite pleasant for working yet, but it is improving.

As the engineering run is completed we will open the dome and vent out the warm air and return to nighttime temperatures and astronomical observations.

Photos from the First Day of Mirror Support Engineering

Here are a few photos from yesterday, the first day of engineering on the Hale Telescope's mirror supports.

Tasks for the first day included removal of the Cassegrain cage. Here is the Cassegrain cage after it was removed. No longer hanging from the telescope it is now sitting on the observing floor.


Here is some of the Palomar Observatory crew installing work lights on the telescope itself (left) and removing the rotating ring (center) from the telescope's mirror cell.

The wide shot below gives a better sense of the perspective of the people relative to the telescope.

Finally (for now) here is a photo taken from under the telescope looking directly up at the mirror cell and the 36 mirror supports. You'll see this photo again as I attempt to explain exactly how the mirror supports work and what work is being done as a part of this engineering run.

Mirror Support Engineering in Progress

If you saw the History Photo of the Week, posted earlier today, you know that we are just beginning a major, multi-week, engineering run on the Hale Telescope to clean and refurbish its 35 mirror supports.

You will be able to take peek at some of the action by looking at the Hale Telescope Web Cam. Unfortunately it doesn't provide too close a look at the action, but I will be posting information and updates here on the blog from time to time.

The action so far today has been mostly directed towards preparing for the work to come. The Cassegrain cage should be removed this afternoon which will provide easy access to each of the supports.

Weather Update: The weather on Palomar Mountain is wonderful right now. The engineering work has kept us from plowing the snow from the public parking area so we are still closed at this time.

Palomar History Photo of the Week - January 25, 2010

This week's Palomar History Photo of the Week shows the 35 of the Hale Telescope's 36 mirror supports in the shop where they were made at Caltech. It is a good time to feature the mirror supports as this week we are entering into a major 5-week engineering run where the telescope's mirror supports will be removed, cleaned and replaced.

Weekend Weather Update

The snow and rough weather has ended on Palomar and the observatory's small weekend crew is still digging out. The observatory will remain closed until it can be properly cleared of snow and ice, which isn't expected until after the weekend.

California Highway Patrol informs us that chains are required and that they are checking to see that people have them. I can say from experience that the roads are very icy. Anyone attempting to visit the mountains should be extra careful. The old adage is don't drive any faster than the the speed you want to crash into something.

The weather brings extra complications for staff at the observatory aside from public safety. This morning I tried to gain entrance to the dome of the 200-inch telescope. While I do indeed have a key to let me in the door marked "No Admittance", the lock was frozen and I could not open the door. Additionally, I am currently snowed out of my office, which is in a different building.

Friday Weather Update

A winter storm warning is still in effect for the San Diego County mountains, including Palomar Mountain. Several inches of snow are on the ground now, with more currently falling. Roads are icy and generally not currently safe for travel. As such, Palomar Observatory is still closed to the public.

Highway 76, beneath Palomar Mountain, from Lake Henshaw to Rincon Ranch Road is currently closed due to mud slides.

The Palomar Mountain Fire Department is recommending that a "Snow Emergency" be declared for Palomar Mountain. This would require all drivers to have tire chains and limit access to parts Palomar, especially to non residents.

All this weather has gotten in the way of some cool astronomy stuff (remember that?) that I am putting off posting for a while. With any luck there should be a lot more of that here on the blog next week.

Weather Update

Palomar Mountain continues to be pounded by the weather and, you guessed it, we are still closed to visitors. Given the weather forecast for the next 48-hours I expect the observatory will be closed through the weekend.

We are strongly encouraging everyone not to travel in the area.


So far we have had fog, trees blown down into road ways, rock/mud slides in the roads, high winds, rain, sleet and snow.

As yesterday drew to a close the snow set in, then it turned to rain. Overnight it snowed and now it is raining again. The rain has given the observatory day crew a chance to clean up a bit in preparation for the next wave, expected later today, that should make conditions worse than they have been all week.

Currently it is raining at the observatory. Winds are around 35 MPH, but I have already seen gusts up to 61 MPH.


Trees weren't the only thing blown down from the high winds earlier this week.

Be safe out there.

Storms Continue. Observatory Still Closed.

Yesterday's storm hit harder than Monday's and delivered rain, sleet, fog and high winds. The maximum wind gust reported at Palomar Observatory was 78.2 MPH at recorded by the weather station at the 200-inch Hale Telescope. There were numerous reports of wind damage and road closures in the area during and just after the storm.

The National Weather Service is forecasting another series of winter storms to hit the area today through Friday (and possibly Saturday). As such it is not recommended that people travel unnecessarily to Palomar Mountain and Palomar Observatory will be closed to visitors again today and possibly for the next several days.