Suppose Earth's axis was perfectly upright (perpendicular to its orbital plane) with $0^\circ$ tilt. What…
Suppose Earth's axis was perfectly upright (perpendicular to its orbital plane) with $0^\circ$ tilt. What would be the consequence for day and night duration throughout the year across all locations on Earth?
Every place on Earth would have equal 12-hour days and 12-hour nights all year long.
The North Pole would have continuous 24-hour daylight forever.
Days would be 18 hours long and nights 6 hours long everywhere.
Seasons would change twice as fast as they do now.
Solution
Without axial tilt, neither hemisphere would tilt toward or away from the Sun at any point during revolution, resulting in equal day and night (12 hours each) everywhere continuously.