Austin JM, Gallant JC, Van Niel T (2013) Mean monthly radiation surfaces for Australia at I arcsecond
and will culminate a few minutes after midnight at an altitude of just under 61.
According to my measurements, as shown in Figure 2, Io and Europa are separated by 9 arcseconds
In small telescopes M76 materializes as a rectangular object 80 arcseconds
long--about the size of the famous Ring Nebula in Lyra.
The celebrated rings, which have been closing since 2003, are currently tilted 14[degrees] (with the south face visible) and appear 45 arcseconds
I'm going to measure the Sun's deflection of starlight too, and to succeed I'll need to determine star positions accurate to a small fraction of an arcsecond
, during only 140 seconds of totality, with no second chance if something goes wrong.
Aim your scope at Mercury around the 28th when its disk is nearly 8 arcseconds
wide and shaped like the first-quarter Moon.
Viewed through a telescope in mid-July, Venus sports a 23% sunlit disk that measures 40 arcseconds
from tip to tip.
This limitation wouldn't be so bad if it weren't for a second one: only a very tiny area of the sky around the star--up to about 30 arcseconds
wide for images at near-infrared wavelengths--will have similar atmospheric turbulence.
Its gibbous disk is nearly 10 arcseconds
wide--big enough to warrant attention from telescopic observers.
Mercury's perihelion precession, due to all causes, is about 574 arcseconds
Its waxing gibbous disk, only 11 arcseconds
wide, proves a small but increasingly alluring telescopic target.
1-magnitude bluish-white star 89 arcseconds
to its northeast.
The Red Planet's disk is now about 13 arcseconds
wide, which is large enough to invite telescopic scrutiny.
8, respectively, with a generous separation of 334 arcseconds