Jupiter takes about 12 years to circle through the zodiac so spends a little over one year in each sign. He is masculine energy and rules both Pisces and Sagittarius; the 9th and 12th houses.
If your age is divisible by 12 (24, 36, 48, 60, etc) you were probably born with Jupiter in Leo (check your natal chart HERE) and this year will be even more special for you - it's your Jupiter return, you lucky duck!
Jupiter is the largest planet in our solar system - in fact if we put all the other planets and the moon and all the asteroids and all the meteors and comets together on a scale - mighty Jupiter would still outweigh them. Astrophysicists believe he was almost our second sun (and he definitely thinks so, too).
Jupiter graciously generates more heat than he receives from the sun - and is associated with expansion, generosity and abundance.
Jupiter is the space that views our life as a journey of prosperity and expansion - from the moment we are born he is widening our vista, nudging us toward new horizons and
So we have the planet of abundance and more moving into the sign (Leo) of abundance and more!
This is an especially powerful year for Leos (sun, ascendants and moons - they need only be brave to have Jupiter with them every step of the way) and also the other fire signs - Aries and Sagittarius (and the air signs, too) and everyone will find the house in their natal chart holding Leo expanding in a good way with this transit!
Read more about this on my Armchair Astrologer blog.