Mon, 09/07/2020 - 17:18
Affiliation
American Association of Variable Star Observers (AAVSO)

Thanks so much for posting this.  I would love to see a picture of this instrument.  (Will we ever again to be able to post images in the forums?)  Is there a date or serial number on the instrument?  Please post more information as you start the restoration.

Here's a discription of the wedge photometry by Edward Pickering (1881):

https://www.jstor.org/stable/25138650?seq=3#metadata_info_tab_contents

Lick's history collection has one of Pickering's wedge photometers (ca 1900). 

http://collections.ucolick.org/exhibits_on_line/E2E.1/Pickering_wedge.h…

Here's another wedge photometer (ca 1920) in the Harvard Collection:

http://waywiser.fas.harvard.edu/objects/12576/wedge-photometer?ctx=a3f9…

We should have a History of Photometry "Observing Section" or at least a forum.  I nominate John Briggs as the moderator.

Phil

Affiliation
American Association of Variable Star Observers (AAVSO)

There is quite a lot of early visual photometry of variables done with various sorts of these photometers (Pickering wedge, polarizing type, etc).  I have keyed-in a bunch of it (thousands of lines of data) for future calibration.  The data have pretty good internal errors, roughly 0.05 mag rms (not all of it, but the careful stuff).  I have wondered if one could rig a 21st Century version of such a device with better control of the artificial star in terms of character (more like an actual star, which seemed to be the main drawback), color, and stability, as well as ease-of-use (e.g. record data in digital form).  It might be a way for strictly visual obsevers to get started by making measurements superior to ordinary methods, and gain an appreciation for fundamentals (zero-points, color terms, etc).

\Brian

Affiliation
None

The AAVSO has or did have a wedge photometer in its equipment archive; came in a nice wooden box.  I have pictures of it, which I can't post, of course.  I was planning on loaning it to a visual observer to see what kind of accuracy was possible.  Thanks, Brian, for giving a rough estimate!  I've heard of other similar devices.

Arne

Arne

This device is dated 1931 and came from Cook Observatory in PA. One item that differs from the "classic Pickering photometer is that in the classic the image of a lamp is focused on a piece of ground glass that blocks 1/2 the FOV of the sky. My Fecker uses a clear glass to reflect the light source into the eyepiece while it transmits the actual sky image.

If someone wants images of this piece, email me at pbealo@comcast.net

Peter

Affiliation
American Association of Variable Star Observers (AAVSO)

Presumably this is the photometer described with extensive observations in this magnus opus:

https://ui.adsabs.harvard.edu/abs/1940PUPFA...5c...1O/abstract

..which is the source publication of early sequences used on AAVSO charts.  One of the more extensive variable-star studies is for the RV Tauri-type variable EZ Aql:

https://ui.adsabs.harvard.edu/abs/1941PUPFA...6c...1T/abstract

The phased lightcurve here gives a good idea of the internal accuracy acheived, but do note that the data-points seem to be averages at variaous phases.  Also the magnitude scale itself was very poorly defined (i.e. not necessarily Pogson) because of the lack of well-defined standard stars anywhere in the sky.  This latter topic is dealt with in the text, but they really had no way of correcting it, so the results are a bit of a mess.

\Brian