Observatory 101 or How to Build an Observatory for Dummies.

 

 Saturday, June 17th   Meinte &  Marsha Veldhuis  arranged a meeting with Tom Melsheimer,  Carole & myself at their home in Berthoud. 

 

Tom Melsheimer has over 35 years experience in building observatories and their equipment including piers, mounts, telescopes and controls.  He is responsible for the design of over 12 observatories including the local observatories here in Colorado: the Little Thompson Observatory, the Observatory Village in Fort Collins and the new observatory in Gunnison.   He has his own company called Meridian Controls http://www.meridiancontrols.com/ with over 20 years of observatory design experience. 

 

Tom is here through Monday and is leaving for Maui again on Tuesday.  His phone number is 970-290-0057 and he is working in his shop in Berthoud.  For two hours Tom went over our plans and commented on details of building a good observatory.

 

His talk can be broken down into:

 

  • General Advice & Comments,
  • Pier Design,
  • Elevation & Telescope Placement, 
  • Thermal Considerations,
  • Electrical Requirements ,
  • General Building

 

General Advice & Comments

  • Never commit to an opening date.  The observatory will be done when it’s done.
  • Never call the warm room a class room.  Classroom has a different implication.
  • Don’t call “star night or star gazing” a “star party”. Party has a different connotation.
  • The LTO was the most important thing he ever did.
  • Two architects were involved with the LTO.  One stamped the structural drawings for the dome and the other was required by the state because it was on school property. 
  • It sounds like Tom Patterson, the principle builder of the LTO, didn’t use the drawings very much.
  • Tom Melsheimer didn’t have a recommendation for an architect. 

 

Pier Design

  • The soil survey will define the type of pier.
  • Absolutely nothing should touch or tie into the pier except the telescope. At least a 1” gap should exist between the pier and anything else.
  • His ideal foundation is a concrete slab on top of bedrock.  If bedrock is less than 5’ below ground two Sonotube (min 12” dia.) caissons can be used with a 12” slab on top. The slab can be 3’ in diameter.  Then another solid pier (18” dia.) from the top of the slab to the base of the telescope.  This can be a hollow cylinder but it’s more difficult to make the end caps.  It’s better to keep it all solid.
  • At the LTO the bedrock was too deep.  They used a “floater” block. A big concrete dead-man (3’ cube) 1/2 out of the ground.  Then a 5’ steel oil derrick from the block to the observatory floor. Then a 12” steel cylinder from the top of the derrick to the telescope mount base.
  • The offset distance from the pier to the center of the observatory dome floor is critical and defines the available floor space for observers. 
  • It is very critical to define true north for telescope alignment.  It cost DU $50K to fix a mistake made on the Mount Evans telescope alignment.  At the site, use a GPS to define the exact latitude and longitude. Use “The Sky” software by Software Bisque on a laptop to define the Sun transient (the local time for the highest point the sun reaches for the day ) to define local noon. Use a plum-bob that will cast a shadow exactly North and South at that instant.

    

 Elevation & Telescope Placement

  • The maximum size scope for the EPMO location is about 14”.  This is because of the turbulent air off the mountains.  The LTO is a little better but not much.  The air is less turbulent and smoother by the time it gets to Berthoud.  The 18” LTO telescope is much too big for the seeing conditions.
  • The spring line is the lowest point the telescope can see and it should be 60 ~ 66” above the observing floor.  This allows short people (students) to see out the dome opening (very important)
  • Make sure the telescope won’t see into people’s houses.  This has been a problem with other installations and can be very costly.  Use the lower door flap on the telescope opening to control the lowest point the scope can observe.
  • A 2’ step stool will allow for the shortest persons to see out the telescope when it is viewing the spring line.  Also, the tallest people will have to be on there knees to view when the telescope is pointing straight up.
  • The intersection of the right ascension (RA) and Declination (Dec) axis of the telescope defines the center of curvature (rotation) of the dome.
  • Try to minimize the height of the steps to the observing floor.  It will result in more available floor area.  The minimum distance between the steps and the observing floor must be more than 80”.  As soon as it reaches 80” there must be an opening in the observing deck floor otherwise people over 6’8” will bump their heads.
  • It may be possible to have a handicap chair lift on the outside of the observatory wall with an opening in the side between the dome spring line and the observatory floor.    It may also be possible to have a chair lift coexisting with the stairs.
  • The stairs should be 42” wide and may be L shaped with a landing.  They should enter the observatory floor in front of the telescope on the South side.

 

 

Thermal Considerations

 

  • Try to eliminate all heat leaks that would cause warm air currents to affect the telescope.
  • Keep the telescope and the observatory at or as near the outside air temperature as possible
  • The dome and warm room roof should be white to minimize stored heating.
  • Use at least 6” of insulation in the warm room to prevent heat leaks.
  • Use electric boilers for hot water heating. No flue gas plumes.
  • Put the observatory dome in the corner of the building.  The two walls will help aid structural support and the location minimizes the roof area (heat waves) the telescope will look over.
  • Have a 6” stub riser all around the dome between the spring line (dome roller line) and the observatory roof so that when snow falls off the dome and ice builds up it won’t cause the rollers to freeze. 
  • The LTO ducted 5 to 6K CFM of air under the observatory floor to the other side of the building in the crawl space to keep body heat and warm air currents from rising into the observatory dome.  30 people in the observatory dome are equivalent to a 15 KW heater.
  • AC is probably not necessary. Use ceiling fans and vent windows. Be careful of placement of vent windows – no air currents in front of the telescope.
  • Use materials that will not store heat for long periods.  No concrete building walls.

 

Electrical Requirements

 

  • Use dual duplex outlets on single 20 amp breaker for each circuit.
  • Use separate circuits for dome, telescope and computers.
  • Use two different circuits for lighting, one for white and one for red.
  • Put ½” PVC tubes into the crawl space through the floor during construction to allow for later additions (i.e., cameras, TV’s electronics, etc.).
  • Ask for 100 amp service.  You may need it later.  The LTO has 45 to 50 and they would like more.

 

General Building

 

  • No opinion on stick built or metal built for the warm room.  Just keep in mind the thermal requirements.
  • The LTO Dome weight is ~3500 lbs.  There is no snow load on the dome.
  • Brewer Steel in Fort Collins made the steel roller rails in 3 pieces for the dome.  Tom welded them together.
  • Lots of I-beam stringers on 8” centers are used in the observatory floor under the LTO dome.  They are tied into the external walls. 

 

 

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By
The Angels Above Foundation