Final answer:
The sun's altitude is greatest at noon in the Northern Hemisphere during summer due to Earth's axial tilt of 23.5°. At this time, the sun reaches its maximum height above the horizon when it is directly overhead at locations on the Tropic of Cancer (23° N latitude).
Step-by-step explanation:
The reason the sun's altitude appears greatest at noon on the Northern horizon is due to the tilt of Earth's axis at 23.5°, which affects the sun's apparent path across the sky. During summer in the Northern Hemisphere, the sun follows a higher arc, reaching its maximum altitude above the horizon at noon. This phenomenon is a result of Earth's axial tilt, which causes the sun to be positioned in the sky at different elevations at different times of the year.
On June 21, often referred to as the summer solstice, the sun appears about 23° north of the celestial equator. At locations on the Tropic of Cancer (23° N latitude), the sun will reach the zenith, meaning it will be directly overhead at noon, achieving the greatest possible altitude. The height of the sun's path in the sky, thus, varies with the seasons, being highest in mid-summer and lowest in mid-winter, due to Earth's tilted axis and its orbit around the sun.