The brightness of the faintest star that can be seen on a given night, is the limiting magnitude
. A number of factors influence this limit, the three most important being aperture, dark skies and experience.
The chart's limiting magnitude
and image scale have always been sufficient for my needs, which typically involved my efforts to accurately align equatorial telescope mounts.
It is for such reasons that the previous revision of Book VI of ARR (Nathan and Weinmann 1999) differentiated between the theoretical and operational estimates of Probable Maximum Precipitation, which has led to several efforts to characterise their severity in terms of their exceedance probability rather than their upper limiting magnitude
(Laurenson and Kuczera 1999; Nathan et al.
It is readily visible when the limiting magnitude
is +5.1 or better, while showing a great deal of detail at +6.1.
Figure 2 shows how the limiting magnitude
changes with focal ratio for a given focal length.
Koos observed up to 3/hr under limiting magnitude
(LM) = 5.8 skies on the morning of 20 January.
A limiting magnitude
, the magnitude of the faintest star visible to the naked eye, was obtained from each observation.
The limiting magnitude
for supernovas would be somewhere between 24.5 and 25.5, corresponding to a distance of about 2,000 megaparsecs or 6.5 billion light-years or 6 X 10.sup.22 kilometers.
I credit my super-dark skies (limiting magnitude
7.5) and young eyes for making such an amazing discovery.
The brightness of the sky--a measure of the amount of light pollution--xxxxalso influences the limiting magnitude
. Fainter stars can be seen in the country than in a city (Table 19).
Observers are reminded to carefully record the observing conditions and the stellar limiting magnitude
, and should also bear in mind the nightly eastwards 'drift' of the Perseid radiant due to Earth's orbital motion.
It was a perfectly clear night with excellent seeing conditions and exceptional transparency with a limiting magnitude
of 6.3 and the target area high up in the sky.