Do the twelve zodiac signs encircle the earth?

Yes the 12 zodiac sign do encircle the earth; as the earth revolves a new zodiac constellation will rise on the Eastern horizon every 2 hours. So that in a 24 hour period all 12 signs will have come an gone only to begin again. Because the earth is also revolving the sun the time that each sign rises changes this allows the viewing of all 12 signs in the night time sky. Also the stars that make up the different signs are not belonging to a single star group but are abstracted by humans on earth over 2,000 years ago. The constellations we see today aren't the same exact images that they saw 2,000 years ago this is caused by our solar systems own revolution around our galaxy. This is known as the precession of the zodiac and the is why the concept of us living in the age of Aquarius comes from the age before this was the age of Pisces lasting about 2,200 years each. I hope this answers your question.