Let's use the "clock-hand" method. Using a circle for the zodiac, with Earth at the center, draw a line from Earth to each placement. So, there's the Sun-hand, the Moon-hand, and so on. Each planet has one also.
Now, let's define the tropical Aries 0 degree point by its Astronomical name, the "Vernal Equinoctial Point", and exclude the tropical Signs altogether. The "V.E.P." , or simply "V.P." is transiting the constellations , retrograde motion, due to a slight wobble in Earth's rotation. This causes the Equinoxes and Solstices to shift through the constellations. Sidereal uses the constellations for its astrological Signs, so there's an Ages clock-hand to go with all the others--a line drawn from Earth, at the center of the zodiacal circle, to the V.P. The location of the V.P. tells us the Sign and degree for the Age, but only in sidereal coordinates
See, when you move to the tropical coordinates, the V.P. is motionless, forever defining the location of the First Point of tropical Aries. Since tropical also should logically have a transiting, Age clock-hand, one that does transit the tropical Signs, a DIFFERENT astronomical point will be needed.