Observation and exploration Although there is no well-defined solid surface within Uranus's interior, the outermost part of Uranus's gaseous envelope (the region accessible to remote sensing) is called its atmosphere .  Remote sensing capability extends down to roughly 300 km below the 1 bar level, with a corresponding pressure around 100 bar and temperature of 320 K .  The observational history of the Uranian atmosphere is long and full of errors and frustrations. Uranus is a relatively faint object, and its visible angular diameter is smaller than 4″.  The first spectra of Uranus were observed through a prism in 1869 and 1871 by Angelo Secchi and William Huggins , who found a number of broad dark bands, which they were unable to identify.  They also failed to detect any solar Fraunhofer lines —the fact later interpreted by Norman Lockyer as indicating that Uranus emitted its own light as opposed to reflecting light from the Sun. 
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This note was uploaded on 12/15/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.