In astrology, there is something called the 0 degrees Aries Point. The 0 degrees Aries Point is 0 degrees Aries, but it links to any cardinal sign: Aries, Cancer, Libra, and Capricorn. This is a sensitive, critical degree with extra special energy compared to the other critical degrees.
The 0 degrees Aries Point connects with 0 degrees of the cardinal signs, which are connected to the solstices and equinoxes, with Aries being the spring equinox, Cancer being the summer solstice, Libra being the autumnal equinox, and Capricorn being the winter solstice. That's right, the start of each season is dictated by astrology!
0 degrees of cardinal signs are critical degrees
0 degrees of the cardinal signs are critical degrees, which are the positions of the start of each Lunar Mansion (a part of Vedic astrology). Every 12 degrees 51 minutes around the 360 degree Zodiac is the start of a Lunar Mansion (to make it easy, we just round to every 13 degrees). Critical degrees have critical energy associated with them, and this energy tends to be challenging until we learn how to harness it. Then it becomes a source of power.
This seems to be especially true to 0 degrees of the cardinal signs. They have a little extra energy associated with them that the other critical degrees don't!
What does 0 degrees of a cardinal sign mean for me?
When you have a planet, asteroid, or angle at 0 degrees of the cardinal signs, that position REALLY wants to come out. Trying to hold it in isn't going to work out too well for you! You'll feel repressed and like you're suffocating, and it'll just be itching, waiting for the chance to erupt. Which might not work out too well!
It's better if you consciously try to use the energy in a positive way in your life. If it's Aries, you need to show your true self with the position; if it's Cancer, you need to show the emotions with the position; if it's Libra, you need to connect with others with the position; and if it's Capricorn, you need to create something solid and real with the position.
If progressed planets or angles come to 0 degrees of the cardinal signs, this can signal an important period for whatever is associated with that planet or angle in your life, and you're often forced to bring something outward, to take more control, and to make things happen.
I used to highly recommend an article by Kim Falconer for placements at 0 degrees of the cardinal signs, however it appears she isn't doing astro work anymore; I was able to find the old article on the internet archives HERE.
0 degrees Aries in the Houses
Even if you don't have any planets or angles at 0 degrees of the cardinal signs, you can see find where 0 degrees Aries falls in your natal houses. That house shows where you connect to take action, moving from the inward to the outward. This is most obvious with the 1st house, since that rules the self; in the 2nd house, it may be with your values; in the 3rd house, it may be with your mind and ideas; in the 4th house, it may be with your core and emotional self; in the 5th house, it may be creatively; in the 6th house, it may be through your work; in the 7th house, it may be through relationships; in the 8th house, it may be through transformations; in the 9th house, it may be through expansion; in the 10th house, it may be though your profession; in the 11th house, it may be through your ideals and dreams; and in the 12th house, it may be through your spiritual pursuits.
0 degrees Aries Point NOW
Mars moves into Aries June 27th, and is at 0 degrees Aries June 27th - 29th. This stimulates the energy for everyone; it'll be strongest if you have any 0 degrees cardinal sign planets, but we'll all feel it (it'll just focus on house for you if you have no 0 degrees cardinal placements).
We also just had a solar eclipse at 0 degrees Cancer, so the energy is ripe right now. We need to focus on manifesting and bringing the within to the external. There is enormous potential in the air right now!
Suggested Reading: Intro to Astrology Houses