From June 18 to 19, the planet will rise with the waning gibbous phase
of the Moon.
The Moon was at a waxing gibbous phase
, less than four days from full, so any effect would have to be glimpsed against a brilliant sunlit surface.
7, and it will be at a rather bright waning gibbous phase
several nights later, seriously hampering observation of the peak of the Perseids, predicted to occur on the night of Aug.
This means that the period around full moon and the two days before and after when the gibbous phase
is particularly brilliant are the favoured hunting win-dow periods to catch them.
Observation of the large gibbous phase
at the start of this elongation will be favourable, as early indications from 2013 May onwards have already shown, but when the planet reaches greatest elongation on 2013 Nov 1 it will be in extreme south declination.
Waxing gibbous phase
; rises after noon, sets before dawn; highest in the sky during late evening.
Its gibbous phase
thickens to 83% lit, while its apparent diameter shrinks from 14 1/2" to 12 1/2".
Spacedex says that viewers across the Northern Hemisphere can best view the shower between 9pm and 4.30am on 13/14 December, but notes that the moon is in the Waxing Gibbous phase
, which may interfere with viewing.
The phase of an outer planet is always full or gibbous (more than half but not all of the disc illuminated); the gibbous phase
is quite pronounced on Mars, but less so on the more distant planets.
The large gibbous phase
is therefore often under-observed, yet records of this phase are those most easily able to define the shape and extent of the characteristic, large Y- and psi-shaped dark markings which can almost always be seen in the ultraviolet and glimpsed--in part at least--in white light.
Over the course of the month, the width of its disk grows modestly from 11 to 13 arcseconds, and the strongly gibbous phase
is obvious in small telescopes.
This month, the brilliant planet fades perceptibly from magnitude -4.2 to -4.0 as its gibbous phase
increases from 63% to 74% sunlit and its disk shrinks from 18" to 15".