<p>The mirrors in UVOT are made of <a href="https://en.wikipedia.org/wiki/Zerodur" rel="nofollow noreferrer">Zerodur</a>, which is one of the favorite materials for telescope mirrors due to its very low thermal expansion coefficient. That is, when the mirror changes temperature, it has (almost no) change in size or shape, which keeps the image quality steady.</p>
<p>The mirrors are, as best as I can tell, coated with a standard combination of aluminum -- which has excellent reflectivity in both the optical and the UV -- and magnesium fluoride, which is transparent in both the optical and the UV and shields the aluminum from oxidation (which would lower its reflectivity). Perhaps there aren't enough oxygen atoms at the orbit of Swift for ongoing oxidation to be a major worry, but the MgF<span class="math-container">$_{2}$</span> coating would certainly protect the aluminum from manufacturing to final assembly and launch of the spacecraft. The same type of coating was used for <a href="https://science.nasa.gov/mission/hubble/observatory/design/optics/" rel="nofollow noreferrer">the <em>Hubble Space Telecope</em> mirrors</a> (though their main material was a different type of ultra-low-expansion glass).</p>

CC BY-SA 4.0
2024-10-10T23:30:55.117Z
The MgF2 coating (but not the aluminum) is confirmed here https://arxiv.org/abs/astro-ph/0507413 It's hard to imagine that the coating is not aluminum, which certainly does have good UV performance [Optimization of MgF2-deposition temperature for far UV Al mirrors](https://opg.optica.org/oe/fulltext.cfm?uri=oe-26-7-9363)
uhoh
CC BY-SA 4.0
2024-10-10T10:34:13.300Z
2024-10-11T03:56:39.487Z
2024-10-11T03:56:39.487Z
Peter Erwin
<p>Question is the title; I am wondering what the mirrors of the Swift Observatory's UVOT made up of, and why these materials were chosen (what was the thought process). I was unable to find anything online.</p>

<telescope><mirror><electromagnetic-spectrum>
What are the mirrors of the Swift Observatory's UVOT made of?
Astrovis
# What are the mirrors of the Swift Observatory's UVOT made of?

(Asked by: username_0 on 2024-10-10)

Question is the title; I am wondering what the mirrors of the Swift Observatory's UVOT made up of, and why these materials were chosen (what was the thought process). I was unable to find anything online.

**Tags:** telescope, mirror, electromagnetic-spectrum

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## 1 answers

### Answer by username_1 on 2024-10-10. Score: 8 | Accepted answer

The mirrors in UVOT are made of [Zerodur](https://en.wikipedia.org/wiki/Zerodur), which is one of the favorite materials for telescope mirrors due to its very low thermal expansion coefficient. That is, when the mirror changes temperature, it has (almost no) change in size or shape, which keeps the image quality steady.

The mirrors are, as best as I can tell, coated with a standard combination of aluminum -- which has excellent reflectivity in both the optical and the UV -- and magnesium fluoride, which is transparent in both the optical and the UV and shields the aluminum from oxidation (which would lower its reflectivity). Perhaps there aren't enough oxygen atoms at the orbit of Swift for ongoing oxidation to be a major worry, but the MgF$\_{2}$ coating would certainly protect the aluminum from manufacturing to final assembly and launch of the spacecraft. The same type of coating was used for [the *Hubble Space Telecope* mirrors](https://science.nasa.gov/mission/hubble/observatory/design/optics/) (though their main material was a different type of ultra-low-expansion glass).

> **Comments:**
> **username_2**: The MgF2 coating (but not the aluminum) is confirmed here https://arxiv.org/abs/astro-ph/0507413 It's hard to imagine that the coating is not aluminum, which certainly does have good UV performance [Optimization of MgF2-deposition temperature for far UV Al mirrors](https://opg.optica.org/oe/fulltext.cfm?uri=oe-26-7-9363)  

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