5 'facts' you learned in school that are no longer true

Over time, even facts we consider steadfast truths can change. People used to think doctors could forgo washing their hands before surgery. Knowledge is ever-evolving.

The seven ideas below probably changed since your school days. Re-educate yourself.

THEN: Pluto is a planet

NOW: Pluto isn't a planet




We've known since the late 1800s that a ninth planet, after Uranus, potentially existed. In 1906, Percival Lowell, the founder of the Lowell Observatory in Flagstaff, Arizona, even began a research project intended to locate the mysterious 'Planet X.'




Then in 1930, a 23-year-old newbie at the facility found it. The discoverer, Clyde Tombaugh, had been tasked with systematically comparing photographs of the sky taken weeks apart to search for any moving objects. He eventually saw one and submitted his finding to the Harvard College Observatory. After an 11-year-old English girl named the new planet (for the Roman god of the underworld), we started including Pluto as a planet in our solar system.




But in 2003, an astronomer found a larger object beyond Pluto -- which he named Eris, according to NASA. The new information caused a bunch of other astronomers to question what really makes a planet a planet, and they decided, based on size and location, that Pluto just didn't make the cut. Neither did Eris, actually. Pluto was demoted to a dwarf planet.

THEN: Diamond is the hardest substance

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NOW: Ultrahard nanotwinned cubic boron nitride is the hardest substance

We've known about two substances harder than a diamond since 2009: wurtzite boron nitride and lonsdaleite, according to Scientific American. The first resists indentation with 18% more fortitude than a diamond, and the second -- a whopping 58%.

Unfortunately, both substances are rather unusual and unstable in nature. In fact, the study's authors, published in the journal 'Physical Review Letters,' only calculated the new substances' hardness, instead of actually testing it using a tangible specimen. That makes the discovery a bit theoretical.

But another contender was published in the January 2013 issue of the journal Nature. In the simplest terms, researchers compressed boron nitride particles to form 'ultrahard nanotwinned cubic boron nitride.' They simply re-organised the particles like an onion, or a flaky rose, or those little Russian dolls that fit inside one another, as the team explained to Wired.

As a result, expect women everywhere to start asking for ultrahard nanotwinned cubic boron nitride engagement rings. Because those really are forever.

THEN: Israelite slaves built the pyramids

NOW: Egyptians workers built the pyramids themselves

Even movies like 'The Prince Of Egypt' perpetuate the idea that slaves built the pyramids. Although many think the Bible tells us they did, the book doesn't mention the story specifically.

This popular myth reportedly stems from comments made by former Israeli Prime Minister Menachem Begin when visiting Egypt in 1977, according to Amihai Mazar, professor at the Hebrew University of Jerusalem.

'No Jews built the pyramids because Jews didn't exist at the period when the pyramids were built,' Mazar told the AP.

Recent archaeological finds actually show that Egyptians built the pyramids themselves. Workers were recruited from poor families in the north and south but were highly respected, earning crypts near the pyramids and even proper preparation for burial.

Slaves wouldn't have been treated so honorably.

THEN: The Great Wall Of China is the only man-made structure visible from space.

NOW: Many man-made places are visible from space.

Technically, this wasn't ever a solid 'truth' -- just a fact third-graders ubiquitously included in their class reports and diorama presentations. In fact, rumours that you can see the landmark, not only from a spaceship, but all the way from the moon, date back as far as 1938.

In 2003 though, the first Chinese astronaut finally shattered the myth.

The party responsible, a man named Yang Liwei, admitted he couldn't see the Great Wall from space, according to NASA.

Other photos surfaced here and there. The consensus became that you can, indeed, catch glimpses of the Wall but only under the right conditions (snow on the structure) or with a zoom-capable camera. You can also see the lights of large cities -- and major roadways and bridges and airports and dams and reservoirs.

The moon factoid, however, is totally wrong.

'The only thing you can see from the Moon is a beautiful sphere, mostly white, some blue and patches of yellow, and every once in a while some green vegetation,' Apollo 12 astronaut Alan Bean told NASA. 'No man-made object is visible at this scale.'

To further clarify, people probably mean these structures are visible from satellites orbiting Earth -- but that's not actual space.