Assuming no typo on your part regarding the "A" satellite, it would be that the moon was the first satellite orbiting earth. If you meant "why is the moon known as a satellite", it's because it is a satellite. Anything that orbits is a satellite.
a moon
Earth is orbited by a large natural satellite known as the Moon.
The only moon known to have a substantial atmosphere is Saturn's moon Titan.
No, Earth only has one natural satellite, commonly known as the Moon.
The moon is a natural satellite of the sun.
That is known as a moon, or as a satellite.
A satellite to the earth.
Earth has one known natural satellite (Moon).
The Moon.
The earth has one natural satellite, popularly known as "the moon". No natural satellite of the moon has been observed.
The Sun is a star. A moon is a (moon) also known as a: satellite.
The moon is a moon, also known as a natural satellite.
Earth's most famous natural satellite is known as the moon.
A moon, when referring to a natural rock like satellite, not a man made artificial satellite such as Telstar.
a moon
The Moon is a satellite.The Moon is a satellite.The Moon is a satellite.The Moon is a satellite.
Earth is orbited by a large natural satellite known as the Moon.