You are a:
I’m taught in high schools around the world.
A mnemonic is a pattern of letters which assists in remembering something, hence mnemonics are often taught in schools to help with learning.
Something that’s described by me is often mispronounced as something bad.
One famous mnemonic involves the names of the planets (e.g. My Very Excellent Mother Just Served Us Noodles - each word begins with the starting letter of a planet, going outwards from the sun). 'Uranus' is one of the planets in this mnemonic, and it is often pronounced in a way that raises a giggle...
Another has something to do with the sun.
Rainbows are made by sunlight interacting with the rain. The colours of the rainbow have their own mnemonic: ROYGBIV (Richard of York Gave Battle In Vain).
Said aloud I can sound a little like an incantation, and for the mathematically inclined I can be very useful.
The inflexions involved in reciting a mnemonic could be described as sounding much like a spell being cast (imagine the witches at the start of Shakespeare's Macbeth: "Double, Double, Toil and Trouble...").
There are many mnemonics for mathematics-related subjects, e.g. I See Octopus Swimming Carefully Eating Lovely Egg Salad (the spelling of ISOSCELES) or Please Excuse My Dear Aunt Sally (Parentheses, Exponent, Multiplication, Division, Addition, Subtraction - the order of mathematical operations).
My ending matches with something that caused a lot of fuss in the late 19th century.
This is the only part I am not entirely certain of right now...
The opposites of my parts can be used to find a greek letter, used right.
Taking 'the opposites' to mean using numbers instead of letters, there are various mnemonics for remembering the digits of the mathematical constant, pi: e.g. How I Wish I Could Calculate Pi (count the number of letters in each word: 3.141592).
I’m a sequence of letters, often capitalised, often memorised.
This is exactly what a mnemonic is!
As for the title:
When mnemonic techniques were first developed by the Ancient Greeks and Romans, it was not in the form of a word or phrase that could be easily memorised. Instead, their mnemonics were "topical" in nature, involving imagining a location or object and assigning specific memories to particular parts of it. From Wikipedia:
The most usual method was to choose a large house, of which the apartments, walls, windows, statues, furniture, etc., were each associated with certain names, phrases, events or ideas, by means of symbolic pictures. To recall these, an individual had only to search over the apartments of the house until discovering the places where images had been placed by the imagination.
In modern-day television terms, this resembles the 'mind palace' technique employed by Sherlock in the Benedict Cumberbatch BBC TV series!