The term "midnight sun" refers to the phenomenon where the sun is visible at midnight or for a prolonged period of time in regions near the polar circles, such as in the Arctic and Antarctic. This occurs during the summer months when the axial tilt of the Earth`s rotation axis is inclined towards the sun, causing the sun to never fully set. Instead, it remains above or near the horizon for the entire 24-hour period, resulting in constant daylight. Option 1, "twilight," is not the correct answer because twilight refers to the period of soft, diffused light before sunrise and after sunset. Option 2, "rising sun," is incorrect because the midnight sun is visible at midnight, not in the early morning. Option 3, "very bright moon," is also incorrect as it does not represent the sun but rather the moon. Thus, the correct answer is option 4.