Origins
Every time you consider a decision, you are — without knowing it — consulting the stars. The word comes from Latin cōnsīderāre, composed of con- ('together, with') and sīdus ('star, constellation'). To consider was to observe the heavens.
In Roman culture, important decisions were rarely made without consulting the sky. Augurs read the flight of birds against the constellations. Astrologers mapped planetary positions. To consider a matter was to study it with the same care that a stargazer studies the night sky.
The astronomical origin produced a beautiful counterpart. The word desire comes from Latin dē-sīderāre — 'away from the stars'. If to consider is to have celestial guidance, to desire is to lack it: the restless longing when the stars offer no answers.
Latin Roots
The related word sidereal (meaning 'relating to stars') preserves the Latin root in its purest form. Sidereal time is star-time — the rotation of Earth measured against the fixed stars.
By the time consider reached English via Old French in the 14th century, the stars had faded from the word's meaning. But the etymology preserves a worldview in which careful thought and celestial observation were the same act.