Re: Questions on my new PMC-8 #EXOS2

Jerry Hubbell - Explore Scientific VP Engineering

On Sat, Nov 23, 2019 at 07:48 PM, AndreaB wrote:
Also, I have the ExploreStars app installed, and I guess the only way to set the tracking from Sidreal to Solar is to actually type in the rate number into the preferences, and not simply selecting it somewhere?
Hi Andrea, welcome to the forum. I realize that it is a bit quirky to not have a pull-down for the different legacy Solar and Lunar rates, but consider the following. The Solar rate is not significantly different from the Sidereal rate as the Sun only lags the stars by 4 minutes in RA in 24 hours. 4 minutes in RA is equal to a 1 degree drift in angular motion per day, or only 2.5 arc-minutes per hour. This rate is not significant when observing the sun over a 10 to 15 minute period at a time and would only result in a drift of 25 arc-seconds in a 10 minute period, hardly noticeable in an eyepiece. This is not significant when doing video imaging of the sun either as you would typically only record a video for maybe 2 -3 minutes at a time. The other significant factor is that even if you corrected the RA tracking rate to the Solar rate, the sun would drift in Declination due to the difference between the ecliptic and equatorial planes. 

It is for this reason that I always suggest to our customers that going to the trouble of changing the tracking rate in ExploreStars is not really necessary for visually observing the sun. We do include a pull-down selection in the PMC-Eight ASCOM driver for Sidereal, Solar, Lunar, and King rates because when doing high-resolution imaging it may be needed, although again, there is no real issue if you do not use those rates.  I think that having these rates is more of a legacy issue and this feature has always been included in tracking mounts since the 1960's. 

Jerry Hubbell
Vice President of Engineering

Explore Scientific, LLC.
jrh at
1010 S. 48th Street
Springdale, AR 72762

Author: Scientific Astrophotography: How Amateurs Can Generate and Use Professional Imaging Data
             Remote Observatories for Amateur Astronomers: Using High-Powered Telescopes From Home

Mark Slade Remote Observatory (MSRO) IAU MPC W54 Equipment
Wilderness, VA
: ES PMC-Eight G11 + Telescope Drive Master (TDM)
Scopes: ES 165 FPL-53 ED APO CF, ES 102 FCD100 ED APO CF
Cameras:  QHY174M-GPS + FW, QHY163C
Misc: 3-inch 0.7x Focal Reducer Field Flattener, Filters: Luminance,
Red, V-band Photometric, Diffuser, 200 lpmm Spectral Grating

Software: MaxIm DL 6, Cartes du Ciel, Astrometrica, AstroImageJ, AutoStakkert!

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