But they are likely tidally locked, so models suggest their permanent daysides could feature lava oceans and a thin atmosphere of vaporized silicates, which could snow onto the very cold nightside.
Observing occultations in infrared radiation also allow for the best constraints on a planet's dayside temperature.
So if Spitzer observes an entire planetary orbit (over the course of a few days for a hot Jupiter), then it will capture thermal emission from both the permanently illuminated dayside and the permanently shadowed nightside.
Phase variations for HD 189733b show that the nightside is only about 400[degrees]F cooler than the 1700[degrees]F dayside, a much smaller difference than expected.
Sandel describes Herbert's more recent versions (shown on facing page) as "round pictures showing auroral brightnesses on the surface of a spherical planet." Because Herbert chose to approximately center the UV-bright areas -- representing the auroras -- in the middle of their hemispheres, and because auroras on the night- and daysides do not mirror each other, these two maps do not portray the skies over diametrically opposite sides of Uranus.
Three bright areas dominate the dayside auroral zone (left map), the view of Uranus facing the sun as Voyager 2 swung past the rotating planet.
The dayside map also includes a fourth diffuse, bright region, located on the upper right horizon at about 30 degrees north by 320 degrees west -- an area near neither magnetic pole.
Furthermore, Herbert adds, this generally accepted model of the Uranian magnetic field predicts the dayside's larger auroral zone should form a long ellipse, with only two bright areas, whereas the three detected by Voyager 2's UV spectrometer give the auroral zone a more circular appearance.