Final answer:
You can tell if you're at the equator, the zero-degree latitude, by observing the celestial equator pass directly overhead, stars rising and setting perpendicular to the horizon, and the sun being directly overhead at noon on equinoxes. Additionally, using a compass at the equator as you cross the prime meridian with the needle pointing north would confirm your position.
Step-by-step explanation:
To determine if you are at the equator, which is the zero-degree latitude, you could observe the night sky. At the equator, you would see the celestial equator pass directly overhead through the zenith. Additionally, the celestial poles would be positioned at the north and south points on the horizon. As the Earth rotates, all stars would rise and set perpendicular to the horizon, and no star would circle the zenith as they would near the celestial poles. Furthermore, on the equinoxes, the sun would be directly overhead at noon. This phenomenon only occurs at the equator, offering a clear indication of your location.
Another method using longitude and latitude involves the recognition that the Earth has 360 degrees of longitude, with the zero meridian passing through Greenwich. At the equator, the longitude can be measured as 0°, with the angle measured east or west of Greenwich, defining your position relative to the prime meridian. It should be noted that if using a compass along the equator, as you cross the prime meridian and face west, the compass needle would point directly north, perpendicular to your direction of travel. This behavior also helps in establishing your position as at the equator.