Here's why:
* Earth's Tilt: The Earth is tilted on its axis, causing different parts of the planet to be closer to the sun at different times of the year.
* Summer Solstice: The summer solstice (around June 21st) marks the point when the Northern Hemisphere is tilted most directly towards the sun. This means that constellations in the Southern Hemisphere, like Sagittarius, are visible higher in the sky at night.
* Opposition: Sagittarius is in opposition to the sun (meaning it's on the opposite side of the Earth from the sun) around late December/early January. This means it's visible all night long during that time period, but it's highest in the sky at midnight around six months later, when the Earth is on the opposite side of its orbit.
Therefore, the combination of Earth's tilt and the timing of Sagittarius's opposition makes late June/early July the time when Sagittarius reaches its highest point in the sky at midnight for observers near the equator.
