When selecting a structure for your observatory, it’s crucial to protect your valuable and sensitive astronomical equipment from the elements. Among the various options, domes stand out as a popular choice. But why choose a dome, and which type is best for your observatory?
Installation of an Astro Haven Clamshell Dome at College of the Desert
The Advantages of Astronomical Domes
Astronomical domes are often preferred over roll-off roof (ROR) structures when housing a single instrument or multiple instruments on a single mount. Domes are particularly advantageous in space-limited environments, as they do not require an adjacent structure for a roof to slide over. They are also ideal for observatories located on top of existing buildings, a common setup for educational institutions and amateur astronomers adding an observatory to a house, or science building.
For public outreach, larger observatory domes are beneficial as they can accommodate visitors in a ring around the telescope, enhancing visibility during tours and orientations. Domes also offer more headroom near the telescope, superior wind protection, and lower horizons compared to similar-height ROR structures. Additionally, they do not require the telescope to be returned to a specific home position to close the structure against inclement weather, or at the end of the night.
A traditional rotating dome from Ash Manufacturing, installed by Sea West at the Rancho Mirage Library Observatory.
Types of Observatory Domes
Observatory domes can be categorized into two main types: traditional rotating domes with a narrow slit-style opening and a protective sliding cover, and non-rotating clamshell domes. Each design has distinct advantages and considerations.
The most popular traditional domes installed by Sea West are Ash Domes, which are made by Ash Manufacturing, a company that has created traditional domes out of Galvalume steel since the early 1960s. Ash Domes are available in diameter sizes as small as 8’ and then 10’-6” through 36’-6” diameters in 2’ increments. With 15 Ash Dome sizes to choose from there is certainly a size available to meet your specific needs.
An Astro Haven clamshell dome observatory built by the Sea West team for Great Basin Observatory. PHOTO CREDIT: Paul Gardner, Observatory Systems
For those who choose to utilize a clamshell-style dome for their observatory, the most popular clamshell domes are made by Astro Haven, which has manufactured fiberglass clamshell domes since 1995. Sea West installs and maintains Astro Haven clamshell domes and they conveniently come in multiple sizes including 7’, 10’-6”, 12’-6”, 16’, 18’, 20’, and 27’ diameters.
An 18’-6” Ash Dome with a PlaneWave CDK700 telescope at the Jackson College Observatory.
Considerations with Traditional Domes
- Wind Resistance: Traditional domes like those from Ash Manufacturing offer excellent wind resistance due to their shape, except when the dome opening and instrument are pointed toward the prevailing wind.
- Mounting Simplicity: Alt-Az mounted telescopes can be placed exactly at the center of the dome, simplifying the design.
- Equatorial Mounting: To center equatorial-mounted telescopes, the pier must be offset from the center of the dome based on latitude. This offset can be as small as a few inches or as large as a few feet depending on the mount’s configuration.
- Synchronization: Traditional domes require software control to keep the dome opening synchronized with the main instrument(s) throughout the night. This synchronization can be complex for off-center telescopes.
- Clearance Considerations: Wall height and diameter must accommodate clearances for the telescope and other instruments when pointed in different orientations with the dome closed.
Another successful Sea West installation of an Astro Haven clamshell dome.
Considerations with Clamshell Domes
- Fewer Moving Parts: Clamshell domes from Astro Haven have fewer moving parts, with hinges permanently aligned east and west and two shutters opening to the north and south. No software synchronization is needed as shutters can be moved as little as once at the start and end of a session
- Flexible Viewing: The shutters can be fully opened for an unobstructed view of the entire sky or partially opened to observe a specific section of the sky.
- Wind Protection: Clamshell domes offer less wind protection when fully open, with some risk of wind from the east or west in all circumstances.
- Telescope Size: Clamshell designs can accommodate slightly larger telescopes compared to equivalent hemispherical rotating domes. It is possible to mount a telescope that may not clear the inside of the structure in all orientations, though this is generally not recommended.
Expert Guidance from Sea West: Dome Installation
Sea West has decades of experience installing both traditional slotted Ash Domes and Astro Haven clamshell domes and can provide expert advice on the best options for your specific needs. Contact us to discuss how we can help you choose the ideal dome for your observatory, ensuring optimal protection and functionality for your astronomical pursuits.