Post by neilbone on May 13, 2008 13:03:55 GMT
There's always a problem with low/dark cirrus appearing in contrast against the twilight arch as a source of false alarms. I have this as a perennial problem in Sussex, where the rest of the sky can appear beautifully clear, but low over the north (in the direction of the South Downs) there's often banded dark cirrus evident against the bright sky. I learned to desregard the possibility of NLC in such circumstances many years ago. If in doubt, a quick check with binoculars usually suffices.
Only very rarely would I be confident in reporting veil-type NLC, lacking binocular-resolveable structure. The sky would have to be utterly pristine! I did see such om 6-7 June 2006, distinguished by a sharp upper edge (exactly where it would normally be in a display at that time of night from this latitude) and silver-blue colour. A lot of it comes down to observer experience.
Above all, it's a case of accuracy rather than breaking records for the earliest sighting and so on. We've had enough trouble with this sort of thing in the realm of meteors over the years (longest watch, brightest fireball, most meteors seen, etc etc). It's NOT a competition; our aim (pardon the pun!) should always be to report accurately and honestly.
In response to yesterday's message re an NLC visibility calculator, graphs showing the time of night at which NLC should be visible on given dates during the season can be found in my Aurora book for 50, 53 and 56 deg north....
Regards,
Neil Bone
Only very rarely would I be confident in reporting veil-type NLC, lacking binocular-resolveable structure. The sky would have to be utterly pristine! I did see such om 6-7 June 2006, distinguished by a sharp upper edge (exactly where it would normally be in a display at that time of night from this latitude) and silver-blue colour. A lot of it comes down to observer experience.
Above all, it's a case of accuracy rather than breaking records for the earliest sighting and so on. We've had enough trouble with this sort of thing in the realm of meteors over the years (longest watch, brightest fireball, most meteors seen, etc etc). It's NOT a competition; our aim (pardon the pun!) should always be to report accurately and honestly.
In response to yesterday's message re an NLC visibility calculator, graphs showing the time of night at which NLC should be visible on given dates during the season can be found in my Aurora book for 50, 53 and 56 deg north....
Regards,
Neil Bone