Mars is the planet of energy and drive, pushing us to take action and go for what we want, when we want it. We can take initiative with Mars, and feel excited about what's possible. We can feel pioneering and enthusiastic, and ready to take action.
In love, Mars brings with it that same energy and drive, helping us to take chances in love and relationships.
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Mars, Transits, & Love Astrology
Mars can help be a catalyst when you first meet someone under positive Mars aspects (conjunctions, sextiles, and trines) to the natal or progressed 5th or 7th house cusps or rulers, or natal Venus. The 5th house is the house of love, the 7th house is the house of relationships and commitment, and Venus is the planet of love and relationships.
You can feel more willing to take a chance, to take the first step, to take initiative, and you don't necessarily have to wait for them to act. You can make the first move with Mars. These aspects don't last very long though, so you've only got a few days to make your move.
Transit Mars in the 5th house can bring extra desire for love and romance, and you can be more open to meeting someone new and exciting, or breathing fresh air into an existing romantic relationship; Mars in the 7th house can bring extra focus on commitment, and you may only be interested in something that can become serious quickly, and can become more committed or take the next step in an existing love relationship; and transit Mars in the 8th house can bring a strong desire for intimacy (or at least a strong sex drive!).
Transit Mars is in a house for about 2-3 months, so you get a longer period to take advantage of Mars energy.
Hard Mars aspects (squares and oppositions) can bring out anger and irritation, and you can feel easily frustrated, so it's usually not the best time to try and work on love! Instead, it's better to keep yourself busy, especially physically.
All hard Mars aspects require you to keep busy to use up the extra energy that the hard aspects stir up. If you don't, that's when lots of fighting can occur, and you can get in some hot water with someone! It can be good for sex though, since that can be a good outlet for the extra energy (though adds to frustration if you're single!).
Mars & Synastry
When you have a Mars connection with someone in synastry, this can show you stir each other to take action. This most likely isn't a connection where you're meant to just kick back together! You can do lots of activities together, and have extra passion together. But you may also fight more with one another than with others, and get under each other's skin sometimes. If everything else is good, then this can be managed, and the fights can be brief and not create any lasting scars.
If you have really good Venus connection to go with Mars, this can create a super romantic connection between you. Venus and Mars go hand-in-hand, playing the astro tango together, and balance each other out nicely (you may want to read the article on Venus conjunct Mars if you've got that!).
In transit, Mars alone won't really give you a lasting connection though, so you do want to see some positive Saturn or Pluto in the mix as well. Otherwise, it may just be a passing fun time!
Suggested Reading: Articles in the Love Astrology Series: Jupiter & Love Astrology, Saturn & Love Astrology, Uranus & Love Astrology, Neptune & Love Astrology, Pluto & Love Astrology, the 12th house, Chiron, eclipses, retrogrades, the Lunar Nodes, and Asteroids of Your Name