Venus at 00.33% phase continuing very bright

10 hrs UTC and bright sunshine near London, therefore after a look at the 4
rather small sunspot groups ~ decided to examine Venus ( 150mm aperture F8
refractor on driven equatorial mount ).

Offsetting by approx 4.75 degrees from the sun ( 1 degree northwards and 20
minutes RA following ) I cautiously removed the objective Baader solar
filter and looked down the tube from the objective end to see how far inside
the scope tube the off-axis sun was shining. O.K. - no problem, only a very
oblique and spread-out illumination, not reaching as far as the eyepiece
tube:- no threat of telescope tube or of optics overheating.
Approaching the eyepiece end of scope the brightness was not uncomfortable,
and I easily observed the crescent Venus , supposedly at 00.33% illumination
yet remaining brighter than minus 3 magnitude.
Best view in local atmospheric conditions seemed to be at around x 100 using
a zoom eyepiece. Using an orange filter did not seem to improve either the
comfort of viewing or contrast of the image.
Surely looks to be more than a 180 degree semicircle of Venusian upper
atmosphere visible in the scope; though I did not have the means to measure
exactly. I really will have to get one of those graticle marked eyepieces
sometime !

Less than 3 days to 00.00 phase , though I suppose even then some light will
be refracted or scattered around the upper Venusian atmosphere, so maybe
this planet never quite reaches 00.00% phase.

Anthony

Anthony Stokes wrote:

and I easily observed the crescent Venus , supposedly at 00.33% illumination
yet remaining brighter than minus 3 magnitude.

Huh? This can't be right -- at its peak brightness, Venus' brightness
is less than -3 (less brightness, not less numerically).

Am I getting this wrong?

Carlos
--

Carlos Moreno wrote:

Anthony Stokes wrote:

and I easily observed the crescent Venus , supposedly at 00.33%
illumination yet remaining brighter than minus 3 magnitude.

Huh? This can't be right -- at its peak brightness, Venus' brightness
is less than -3 (less brightness, not less numerically).

Am I getting this wrong?

Yup, at peak brightness (around last May 10th ) Venus was mag. -4.2.

Bart

In article t,
Bart Declercq wrote:

Carlos Moreno wrote:

Anthony Stokes wrote:

and I easily observed the crescent Venus , supposedly at 00.33%
illumination yet remaining brighter than minus 3 magnitude.

Huh? This can't be right -- at its peak brightness, Venus' brightness
is less than -3 (less brightness, not less numerically).

Am I getting this wrong?

Yup, at peak brightness (around last May 10th ) Venus was mag. -4.2.

Peak brightness occurred around 1 May, and was -4.5

The "traditional" peak brightness of Venus was -4.4 but during the
1980's the magnitude formulae for the planets were revised to be
based on more modern measurements, and nowadays Venus magnitude is
given as reaching -4.7 at the brightest peaks.

The problem with obtaining accurate magnitudes of such bright objects
is that there are no standard magnitude stars of comparable brightness.
The magnitude of Sirius was commonly given as -1.6 in the 1960's
and earlier, but nowadays Sirius is considered to be of magnitude -1.4

The magnitude of Venus, when faintest, is a little fainter than
magnitude -3. This is due to the atmosphere of Venus refracting the
sunlight, making Venus much brighter at thin crescent phases than it
would have been without an atmosphere. The brightness of Mercury,
for instance, drops off rapidly at thin crescent phases and I don't
think anyone has ever successfully observed Mercury as a very thin
crescent.

Btw Venus may even appear _brighter_ as it approaches the solar limb
on 8 June, since the sunlight will then be refracted by Venus
atmosphere towards us all around Venus' limb. Whether Venus then
gets bright enough to be visible through a colar filter remains to be
seen... if it does then THAT's the moment of Venus' peak brightness
(magnitude -12? -15?).

By conicidence, the Moon's brightness when faintest (as viewed from
the Earth) is also a little fainter than magnitude -3, i.e. nearly
the same as Venus' brightness when faintest (again as viewed from the
Earth). But in the case of the Moon, the reason is different: this
minimum lunar brightness is due to earthshine.

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://www.stjarnhimlen.se/
http://home.tiscali.se/pausch/

Paul Schlyter wrote:

The "traditional" peak brightness of Venus was -4.4 but during the
1980's the magnitude formulae for the planets were revised to be
based on more modern measurements, and nowadays Venus magnitude is
given as reaching -4.7 at the brightest peaks.


With the publication of _The Astronomical Almanac_ for 2005, the
formulas predicting the visual magnitudes of both Venus and Mercury
have been revised again, a change prompted by the yet-unpublished work
of the USNO's James L. Hilton. We may have to wait until the next
edition of the _Explanatory Supplement_ (now being revamped, I'm told)
to learn the underlying details.

--
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Mark Gingrich San Leandro, California