How many officially recognized planets are in our solar system?

How to get close to this number

Almost everyone learned a number for this, and for anyone over about thirty that number is wrong by one. The question is not what the planets are but when you learned them, which makes this a rare case where the right answer depends on your age rather than your knowledge.

The reclassification in the explanation was a definitional decision, not a discovery. Nothing about the object changed; astronomers agreed a definition of "planet" that requires clearing the neighbourhood around its orbit, and one body failed that test. Categories in science are tools, and tools get redesigned when they stop working.

The reason the definition needed tightening is the part usually left out. Increasingly large objects were being found in the outer solar system, and without a boundary the count would have grown indefinitely as detection improved. The choice was between eight planets and an ever-expanding list, which makes the decision a practical one rather than a demotion.