The Thematic Mapper (TM) is an advanced, multispectral scanning, Earth resources sensor designed to achieve higher image resolution, sharper spectral separation, improved geometric fidelity and greater radiometric accuracy and resolution than the MSS sensor. TM data are sensed in seven spectral bands simultaneously. Band 6 senses thermal (heat) infrared radiation. Landsat can only acquire night scenes in band 6. A TM scene has an Instantaneous Field Of View (IFOV) of 30m x 30m in bands 1-5 and 7 while band 6 has an IFOV of 120m x 120m on the ground. (source #11)

Atmospheric condition at any given time or place. Compare with climate. (source #2)

Marked by brilliant sunlight : full of sunshine. Bright and shiny. (source #5)

Between 3/8 and 5/8 of the sky is covered by clouds. (source #4)

Side note- A better representation of the fraction 3/8 and 5/8 is by using an example of a pizza to represent each of these. 

When 7/8ths or more of the sky is covered by clouds.  (source #4)

Side note: A better representation of the fraction 7/8 is by using an example of how a pizza has 8 slices and one of the slices is missing.