We are excited to announce the launch of our new forums! You can access it forums.aavso.org. For questions, please see our blog post. The forums at aavso.org/forum have become read-only.
Announcement: New Applications
We are excited to announce the launch of our new applications! We're opening up early access to our new applications for searching, downloading, and submitting photometric observations. You can now access these applications through these links:
We ask for your feedback in order to help us improve these applications. Please send feedback for the applications above to feedback@aavso.org. Note: please avoid duplicating submissions across the two submit applications.
It is straightforward to take twilight flats against a cloud-free sky using filters. I do this essentially every clear night with a Sloan u filter. It is best to point the telescope near the zero-gradient 'Chromey spot', which is roughly 15 deg off the zenith along an azimuth opposite the Sun. This time of year, this is at a Declination somewhat north of your latitude. Just doing it at the zenith may be good enough with small telescope fields. With an f/8 system I start the u flats at about Sun elevation -2 deg, but you will have to experiment with this. In any case, it will be quite a bit earlier than one would do twilight flats in B and V filters (say).
It is straightforward to take twilight flats against a cloud-free sky using filters. I do this essentially every clear night with a Sloan u filter. It is best to point the telescope near the zero-gradient 'Chromey spot', which is roughly 15 deg off the zenith along an azimuth opposite the Sun. This time of year, this is at a Declination somewhat north of your latitude. Just doing it at the zenith may be good enough with small telescope fields. With an f/8 system I start the u flats at about Sun elevation -2 deg, but you will have to experiment with this. In any case, it will be quite a bit earlier than one would do twilight flats in B and V filters (say).
\Brian
Steve