Final answer:
The Egyptian civilization created an accurate 365-day solar calendar based on the yearly cycle of the bright star Sirius and the flooding of the Nile River.
Step-by-step explanation:
The civilization that created an accurate 365-day solar calendar were the Egyptians, approximately 3000 years ago. They meticulously observed the rising time of the bright star Sirius in the predawn sky, which had a yearly cycle aligning with the flooding of the Nile River.
Other ancient cultures, such as the Babylonians, Assyrians, and Chinese, also developed their own calendars around the same period. The 365-day calendar of the Egyptians influenced the development of later calendar systems, including the Julian calendar introduced by Julius Caesar, which further refined the year's length with the inclusion of leap years to more accurately reflect the solar year.