
He Drew the Sun for 40 Years, but Now His Telescope Is Dying - bpierre
http://www.wired.com/2016/04/man-whos-drawn-sun-almost-every-day-40-years/
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nmcveity
If you are in the LA area you can take a docent guided tour of the Mount
Wilson facilities, including the solar observatory mentioned in the article
and the dome where Hubble observed.

For someone interested space and astronomy, it was a thoroughly enjoyable day.
The view from the San Gabriels into the LA basin is also a marvel.

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exDM69
The Mt. Wilson observatory is also the last of the giant telescopes to use a
traditional equatorial mount, where the axis of the mount is parallel to
Earth's axis of rotation. In other words, it's got a giant steel mounting that
needs an entire building foundation to support it.

An equatorial mount was required in the days of photographic plates, the mount
is turned to compensate the rotation of the Earth during long exposures. This
can be done by rotating the axis with a steady rate.

Modern (giant) telescopes use alt-azimuth mounts (similar to a normal camera
mount), which require two axes to be adjusted simultaneously with computer
control. This causes the projected image to rotate and is not suitable for
photographic plates but can be compensated with digital image processing.

I'd like to visit the Mt. Wilson observatory just to see the marvelous
engineering in the mounting.

~~~
privong
> In other words, it's got a giant steel mounting that needs an entire
> building foundation to support it.

This is still the case for the Alt-Az telescopes. For stability, telescopes
are built on a foundation that is independent from the building's foundation
and, ideally, that goes to bedrock.

> Modern (giant) telescopes use alt-azimuth mounts (similar to a normal camera
> mount), which require two axes to be adjusted simultaneously with computer
> control. This causes the projected image to rotate and is not suitable for
> photographic plates but can be compensated with digital image processing.

Actually, there's usually a third rotation axis often added to instruments (or
their mount points) for Alt-Az telescopes, called a field rotator. As one
might expect, this counteracts the apparent rotation of the field and
maintains the same image orientation on the detector. Note that this is also
important for spectroscopy and not just imaging. For spectroscopy, you may
also want to ensure the position angle of your slit is constant relative to
your source of interest, particularly if the source is not point-like.

In principle, one could correct for the field rotation with image processing.
But for many observing programs, the individiual exposures can be in excess of
15 minutes. For crowded fields or extended sources, it would be non-trivial to
deconvolve the field rotation. In practice, it's much easier to just add a
third axis to the instrument which counteracts the field rotation.

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spdustin
There's also a model-specific wedge that can be used to "convert" to
Equatorial. My SCT has one available, though I don't use it, since most of my
imaging involves stacking much shorter exposures at lower magnifications than
would be problematic with field rotation.

~~~
privong
Good point. Those are available for amateur telescopes. I should have noted I
was referring to professional University or national-level observatories.

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codingWithGit
It will be awesome if someone can animate these into a movie or a gif.

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wmeredith
How in the hell does this article get published without an image of one of the
drawings?

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wglb
These drawings seem to be very hard to find.

~~~
numlocked
[https://www.google.com/search?q=solar+drawings+mount+wilson&...](https://www.google.com/search?q=solar+drawings+mount+wilson&espv=2&biw=1680&bih=951&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjc8Jmh4u7LAhUHKWMKHXFlBAQQ_AUIBigB&dpr=2)

