Each planet has aspects on certain houses. All planets have 7th aspect from where it is situated. In other words it sees the 7th house from its location.
But Jupiter, Mars and Saturn have two extra special aspects.
Jupiter aspects 5th and 9th place from its location
Mars aspects 4th and 8th place from its location
Saturn aspects 3rd and 10th place from its location Some say Rahu and Ketu aspects 5th and 9th place from its location (Some astrologers deny it). I personally do not consider this particular aspect of Rahu and Ketu.
What do aspect really mean ?
Aspect of the planet means vibrations of the planet. For example, if Saturn aspects 10th house from where it is located then the vibrations of Saturn have been transmitted in the 10th house. Each planet through its aspect creates an effect in the house according to its nature. The aspect of planets is considered to be an important part in matter of prediction.
Aspect of a planet is always powerful. For example, if Sun in Thula aspects Saturn in Mesha through its 7th aspect. Then Sun weakens the effect of Saturn in mesha as Sun is transmitting its vibrations.. Similarly, Saturn weakens the effect of Sun in Thula as Saturn is also transmitting its vibrations through its 7th aspect.
To explain in a simple way:
You are going to temple to see the God/Goddess idol in turn they see you. Hence the vibrations are felt by you when you worship them, so that you may get peaceful mind and good thoughts arise. It is the same when you go and sit in front of a powerful yogi or saint. When they just see you, you feel their vibrations.
To understand better the common statement used by people “Don’t cast evil eyes on me”, “They had cast evil eyes on us”. This it to just show the power of aspect in real life situation.
Now look into your own horoscopes where does each planets have its aspects on.