Revelations 12/1 And a great sign appeared in heaven: a woman clothed with the sun, with the moon under her feet, and on her head a crown of twelve stars. She was pregnant and was crying out in pain from the birth and the agony of giving birth. And another sign appeared in heaven: behold, a great red dragon, with seven heads and ten horns, and on his heads seven diadems. 

The first sentence sets the scene. A great sign appears in heaven. Which heaven are we talking about? The next part tells us. The heavens we associate with the sun, the moon, and the stars. This is a sign in the constellations. For these celestial elements to line up like this is very rare indeed. However, they did align in this picture in September 2017. It will not happen again for another 10,000 years. This is a starting point for Rev 12. It also looks to be the start of the end of the age events. Not the beginning of the last seven years. At the same time, the constellation of Draco the Red Dragon rose to about a third of the way up in the night sky as viewed from Israel.