Re: Stars in daylight
- From: canopus56 <canopus56@xxxxxxxxx>
- Date: Wed, 19 Dec 2007 20:07:43 -0800 (PST)
On Dec 18, 2:49 pm, skatebi...@xxxxxxxxx wrote:
Is there anybody whohas seen stars in daylight, which means:
- Sun above the horizon
- Naked eye, i.e. no optcal device other than normal eyeglasses used <snip>
The following two articles may be of interest:
Weaver, H. F., The Visibility of Stars Without Optical Aid. PASP
59(350):232. 1947PASP...59..232W
http://adsabs.harvard.edu/abs/1947PASP...59..232W
Garstang, R.H. 1985. Visibility of Stars in Daylight. British Astron.
Assoc. J. 95(3):133. 1985 JBAA...95..133G
http://adsabs.harvard.edu/abs/1985JBAA...95..133G
In Weaver's 1947 article, he summarized his predications for unaided
eyes (in Table VII) in terms of a limiting magnitude based on the
zenithal distance of the star (alpha) and the angular distance between
the star and the Sun (beta) above the horizon. In 1985 Garstang
confirmed Weaver's daylight limiting magnitude formula using
photoelectric measurements of the daytime sky. Garstang also extended
Weaver's computation to a star-Sun angular distance of 90 degrees.
Weaver concluded that no stars are visible to the unaided eye during
daytime. A recent notable exception was Comet McNaught C/2006 P1 that
peaked at a magnitude -5.1 on Jan. 14 of this years. The magnitude of
Venus around maximum elongation is about -4.1. Garstang noted that
the two brightest: Sirius and Canopus can be seen with the naked eye
20 minutes before and at sunset, respectively.
Weaver's Table VII with Garstang extension
Daylight limiting magnitude
beta (degs)
alpha 0 30 60 90
0 -3.0 -2.8 -2.5 -3.6
30 -3.0 -2.9 -2.6
60 -3.4 -3.3 -3.2
80 -4.7 -4.8 -4.8
The apparent magnitudes and names of the 12 brightest stars (excluding
the Sun) visible:
Sirius -1.44
Canopus -0.62
Arcturus -0.05
Rigil Kent A -0.01
Vega +0.03 +0.58
Capella +0.08
Rigel +0.18
Procyon +0.40
Achernar +0.45
Betelgeuse +0.45
Hadar +0.61
Altair +0.76
The above says nothing about the visibility of stars through the
_aided_ eye. Nighttime limiting magnitude calculators, usually based
on Schaefer's algorithm, will not return useable results for the
daytime visibility of the stars. E.g. -
http://members.csolutions.net/fisherka/astronote/astromath/SchaeferLMCalc.html
In the current issue (Dec. 2007) of the Brit. Astro. Assoc. J.,
Scottish amateur John Vetterlein explains his procedure for aligning a
Synta EQ6 mount during the daytime, noting that "Arcturus, Capella and
Vega . . . are bright and readily visible in good, clear skies with
apetures of 80mm or more [used at low 22 power]." John drills three
holes in a stone slab and polar aligns his mount at night. Using
those reference marks, he sets up during the daytime on the following
day. His three bright stars provide reference points for two-star
alignment. Then he can use Goto to zero in on Venus (-4.1) and Mars
(max apparent -1.5). Of course, the Moon is visible during the
daytime from the 1st through 3rd quarters (quarter Moon -10v; full
Moon -13v).
Vetterlein, J. Dec. 2007. 'GoTo' telescopes and objects in daylight.
Br. Astro. Assoc. J. 117(6):345.
Hopes that helps.
- Canopus56
.
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