In this video, Scottie Clark (who discovered this alignment using astronomy software a few years ago) explains the differences. It's well worth watching and includes a demonstration of the sign (Released Sept 21 2017; 33 mins).
{Post Edit added 9th Oct:To those who are not aware, a 1900 year old Biblical prophecy in the book of end times, Revelation, matches in detail, a celestial alignment that occurred on September 23, 2017. This is a message, or signal to all of humanity, that dramatic change is around the corner. I'm sure you will agree, even the past couple of months have not been "normal" - however it's just the beginning.
So - in summary, September 23 was a marker in time, heralding the beginning of the events and plan of Revelation.}
Here's his intro:
The mainstream fake news is trying to make Christians look stupid again because of possible upcoming signs in the heavens. Here is what you should know. Christian researchers agree, the world will NOT end in 2017, but prepare for change!
Learn about the difference between the Star of Bethlehem and the Revelation 12 Sign as they are NOT the same.
Learn why no one has adequately debunked the Revelation 12 sign of September 2017. Learn why this date is so massively popular.
And for the 500th time (to the haters), I am not setting a rapture date with my research. Make the distinction between the astronomy software and the Scriptures, but also realize the link between the scriptures and the alignment. It could very well be something huge, and with everything else going on, it is certainly not nothing. Wake up!