What is the chart ruler?
Most modern astrologers will tell you that the chart ruler is the ruler of the Sign on the ascendant. The ascendant is the degree of the sign on the eastern horizon at the time of birth. Some astrologers will tell you that the chart ruler is the almuten, aka alumtem (short for almutem figuris), of the rising degree. This is usually, but not always the, ruler of the sign. It is determined by finding the planet that has the greatest strength, by essential dignity, in the rising degree regardless of where it is in the chart. Libra rising is a good example of a sign that might have something other than Venus as almutem. Saturn is exalted in Libra as well as the triplicity ruler of air and can be stronger than Venus in day charts. Both of these methods have the same weakness: the ruler of the sign or the almutem of the degree, might be very weak in a particular chart. Who wants a weak planet as chart ruler? So go with your strength use the strongest planet by essential dignity in the chart that can act. IN other words a planet in the 6th, 12th or 8th might have the most essential dignity, bu the number two planet that is posited in the 10th house is preferable. The beauty of this idea is that you get to work with a planet using your free will to develop your strengths and those strengths are shown by the strongest planet. A famous psychologist, Abraham Maslow wrote quite a bit about self-actualization, or the process of becoming all that you can be. A self-actualizer is a person who is living creatively and fully using his or her potentials. "Using your potential" is another way of saying "working with and realizing your strengths." Those strengths are shown by the strongest planet in the chart. The native supplies the work. This dominant planet stuff that floats around here is an attempt to find the strongest planet, but since some of the dominant planets are actually in their detriment or fall, I would disregard the idea.
In an astrological chart, what is the ruling planet?
Modern astrologers make the ruler of the ascendant the "chart ruler." This is quick and dirty but it ignores two facts: 1) the domicile ruler may be in detriment, say you have Capricorn rising and Saturn is in Leo, your "ruling planet" is weak and malefic. Who wants a chart ruler like that? 2) It ignores the exaltation ruler. If you have Cancer rising and the Moon is in Scorpio (fall) and Jupiter is in Sagittarius, wouldn't it be better to have Jupiter ruling your chart and so why not? The best way to find the chart ruler is to look for what used to be called "The Lord of the Geniture." The Lord of the Geniture is the strongest planet in the chart by essential dignity with this one exception. If the planet with the most essential dignity is poorly placed, let say in the 12th or 8th, you might wish to use the next strongest planet if it is well placed. Why do I give you a choice? Because astrology is not all that fatalistic. You can choose to use the strongest planet in your chart, the life you want, or you can stay stuck with the domicile ruler of the ASC, the life you were given. As always it is your choice.
Why is Saturn my chart ruler?
Posting your whole chart will help. The ruler of the Ascendant is said to be the chart ruler and in traditional astrology it rules the self. I think it depends on the type of analysis the most. For example, the Walter Pullen analysis on astro.com will give you dominant planets I guess based mostly on rulership. The outer planets are said to be felt only if they make tight aspects to personal planets. Kevin Burk claims the relationship to outer planets is largely determined by our relationship with Saturn. And being in right relationship with Saturn I guess is not something a lot of people will be fond of: deadlines, self-discipline, hard work, asceticism. I would suggest looking at the house where Saturn is in your chart, also the sign, and maybe those play a bigger part in your life than you think, who knows.
How important is the chart ruler?
I'm not really sure. Whatever has the most aspects coming off it is usually the most powerful, ones that are in conjunction to one of the 4 angular points (ascendent, descendent, midheaven and imum coeli) are considered powerful too. Your chart ruler can also be the sign that rules your ascendent. Yours would still be the same, as Pluto rules Scorpio. Mine is Taurus as that is my Mercury sign, and Mercury rules my Virgo ascendent, Mercury is also conjunct the midheaven. Singleton planet's are considered to have a strong influence too. My moon is a singleton, at the point of a T-square, so I guess that and mercury are my charts "rulers". Pluto is my most aspected planet, so that has a strong influence too. Whatever sign is in the planet that rules your sun is said to be important also. You have to take more things into account than just your first house and its placements. Anyway, the Scorpio/Pluto energy in your chart would be amplified and more pronounced with Pluto in the first, considering it rules the ascendent and is in arguably the most important house.
What are the indications that jupiter is your chart ruler?
The concept of a ruler or the chart is alien to Vedic Astrology. We frequently find the use of this term in the Sun-sign based yearly, monthly, weekly and daily predictions given by western astrologers.However, The Tajak Shastra, which admittedly is an adaptation from Arabic Astrology, gives the method of the determination of a yearly lord for each years’ progressed chart.The basic consideration is the strength of the Planet subject to the condition that it must also cast an aspect on the rising sign.If you are keen on finding out whether or not the planet Jupiter is the Ruler of your chart, you can use the Tajak method for your birth chart.
Chart ruler in 12th house, what it means?
The 12th is traditionally the house of secrets, hidden things, and self undoing. In old astrology it was said if the ASC ruler was in the 12th the native would end up in slavery. Today we might say that we put ourselves in such positions that we end up dominated by others usually because we don't speak up for ourselves or act in our own best interests. You didn't say what sign Mercury was in or what aspects are made to Mercury. This is very important. If Mercury is in mutual reception with a good planet or in aspect to its dispositor, a lot of the bad 12th house stuff is negated. Mercury in Gemini in the 12th isn't so difficult. If Mercury is in Taurus look at Venus and see if she is somehow connected to Mercury. That could be very beneficial. Another possibility is that Mercury in the 12th indicates hidden talents that are not developed. Without seeing the chart it is difficult to pinpoint any of this, but I'd say spend some time thinking about yourself, what you want and how you want to live your life, then work at making those things happen. If you let events blow you along, you will end up hurting yourself, and fulfilling the negative potential of the chart. ON the other hand, you could write mystery stories. That would be a great Mercury in the 12th expression. Modern astrologers will tell you that the 12th has to do with being spiritual. It doesn't. That's 9th house stuff.
What if one's chart ruler has no aspect with another planet or an ascendant?
It is really hard to comment on this situation because you have not included your birth data.There are times when you have to look at the dispositor of the ruler of your chart.Thus, if Sagittarius is the Rising sign and you then look to Jupiter (Ruler of the chart).Now, let’s say that Jupiter is in Capricorn (with no aspects to it). In this case, I would be obligated to look at the aspect structure connected to Saturn the ruler of Capricorn.Also, I would want to discuss with the client the activity of the House where the ruler is located.It is truly remarkable how adaptive and flexible human beings are.