A somewhat literary or poetic term for the vast sky or heavens, often with a grand or spiritual nuance. In everyday speech, 空 (そら) is more common.
The sight of an eagle soaring through the sky is beautiful.
Countless stars shone in the night sky, and the heavens were like a jewel box.
He longed to be a bird flying freely through the sky.
Atop that mountain stood a building like a castle in the sky.
A sky full of stars spread across the heavens.
天空 is a formal, literary term for the heavens, whereas 大空 is more commonly used in everyday poetic or descriptive speech.
地上 refers to the ground or earth's surface, the physical opposite of 天空, the sky above.
magnanimous; broad-minded; as open as the sky and serene as the sea
Compound of 天 (てん, 'heaven') and 空 (くう, 'sky'). The reading てんくう is the standard on'yomi combination.