What is the difference between an umlaut and diaeresis?

Related questions

1. How does an umlaut change the sound of a vowel?
2. What does Ü mean in German?
3. How do you type an umlaut on Facebook?
4. How do I type German letters on my computer?
5. How do I put two dots above a letter?
6. Does naive need the umlaut?
7. How do I put an umlaut over a letter in Word?
8. How do you type Ü?
9. How do you type accents on an iPad?
10. How do you type a German double s on a Mac?

Tags

1. #pronounced
2. #first
3. #heiresses
4. #divide
5. #diaeresis
6. #syllable
7. #mistaken
8. #vowel
9. #umlaut
10. #separate
11. #crucial
12. #actually
13. #second
14. #forms
15. #diphthong
16. #often
17. #greek
18. #indicates
19. #those