put a voltage of 2.73V + (X * 0.01V) where X is the temperature in degrees Celcius. The analogRead command digitises this analogue voltage to a whole number in the range 0 to 1023 with 0 corresponding to 0.00V and 1023 corresponding to 5.00V.
Source: Arduino Solar Water Heating Pump Controller Design and Code | REUK.co.uk