Did these appear only to John?

Revelation 12:1a And there appeared a great wonder in heaven; 

Revelation 12:3a And there appeared another wonder in heaven;

Or will they both appear to everyone in heaven?

Or will they also appear to those on the earth?

I doesn't sound like constellation & planet lineups that many of us were so excited about, recently.

That's because line 4 mentions "stars of heaven":

Revelation 12:4a And his tail drew the third part of the stars of heaven, and did cast them to the earth: 

So, if the stars of line 4 are explained by many to be angels, not actual stars, then why is line 3 explained to be a constellation?

Also, how does a constellation cast angels to the earth, anyway?

And even if the stars of heaven in line 4 are explained to be actual stars, how would a constellation cast other stars to the earth?

Or if the stars of heaven in line 4 are explained to only be meteors (meteorites), then were there massive meteorite strikes, with the meteors coming from the constellation that many of us were watching recently?