Part 1 - The sun moves along the ecliptic which takes it through some vary familiar constellations such as Gemini, Sagittarius, Virgo, etc. The 12 constellations are collectively known as the zodiac. But careful observations shows that the moon and all of the planets never stray far from the zodiac. Your mission is to offer a simple explanation (using your own words) why that is. In your answer explain why Pluto can stray quite far from the zodiac at times.
The earth revolves around the sun which defines a plane in space. The Zodiac is simply a projection of that plane onto the celestial sphere. It should be crystal clear why the sun, then, is always seen within one of these Zodiac constellations (defining the ecliptic). So why are all the other planets seen within the Zodiac? The solar system is flat!!!! That is to say, the orbit of all the other planets lie (almost) on that same plane. Therefore, all the planets appear in the Zodiac as well. Pluto, however, has an orbit that is inclined by 17 degrees to the orbital plane of the earth. It can stray quite a way from the Zodiac.
Part 2 - You should have already read about the wobble in our axis known as precession. If you go 13,000 years into the future (about half a precession cycle), will the zodiac still be defined by the same constellations? (This is relatively easy to discover if you've learned the Stellarium program.) Explain why or why not.
Let the earth wobble all it wants. Let its tilt angle change. Do whatever you want to the earth .... but as long as the earth orbits on the same plane (and it will) .... the sun will always be seen in the Zodiac. Note: Precession will change which constellation we see the sun in, say, the first day of spring. However, it will always be seen in the Zodiac.
Another way to see the answer is by realizing that astrology used the zodiac constellations for about 4000 years ... and they still are in use today. I know 4,000 years is not a lot compared to the 26,000 year precession cycle, but it has been enough to shift your birthday sign about 1 constellation to the west. That shift, however, is still in the zodiac! You could see this for yourself if you already learned the Stellarium program. Set it up so you track the sun, remove the atmosphere and ground, draw in the constellations and their names, ... then go 13,000 years into the future. You will see as you flip through the months that the sun will still be moving along the same old zodiac.