Vowels vary enormously from speaker to speaker. Also, different dictionaries use different symbols to represent sounds; some use IPA, some don't.
I'll begin with the vowel chart:
This chart depicts a schematisation of two dimensions of tongue movement, demarcating the boundaries of the vowel articulatory space within the oral cavity. The slanted line to the left marks vertical displacement of the front of the tongue, showing us different degrees of open/close approximation i.e. how far or near the tongue is positioned from the roof of the mouth.
- Open vowel: the tongue is positioned as far as possible from the roof of the mouth e.g. [a ɑ].
- Close vowel: the tongue is positioned as close as possible to the roof of the mouth without creating a constriction e.g. [i u]
- Other vowels such as near-close, close-mid, mid, open-mid, near-open etc., lie in between open and close vowels.
The horizontal lines mark vowel backness i.e. whether the highest part of the tongue is positioned in the front or the back of the mouth.
- Front vowel: the highest point of the tongue is positioned relatively in front in the mouth e.g. [i e æ ɛ]
- Back vowel: the highest point of the tongue is positioned relatively back in the mouth [u ɑ ɔ ʌ]
- Central vowel: the tongue is positioned halfway between a front vowel and a back vowel [ɜ ə ɐ]
There's another feature called vowel roundedness which refers to the amount of rounding in the lips during the articulation of a vowel. In the chart, some vowels occur in pairs such as [i, y], [ɨ, ʉ], [ɛ, œ] etc., the ones to the right side are rounded (the lips are rounded while producing that vowel) whereas those to the left side are unrounded (unrounded lips).
[Some information about the vowel chart has been adapted from Understanding Phonetics by Patricia Ashby]
Here are some transcriptions for scary from dictionaries that use IPA:
- Scary → /ˈskɛːri/, /ˈskɛəri/, /skɛri/
it can either be pronounced with a long vowel /ɛː/ or a short one /ɛ/ (the only difference is 'vowel length', not 'vowel quality'), or even with a diphthong /ɛə/ (it involves a change of position of the tongue i.e. from /ɛ/ to /ə/). /ɛ/ is called open-mid, front, unrounded vowel: it's a front and unrounded vowel. In articulating [ɛ], the tongue is positioned one-third of the way from an open vowel [a] to a close vowel [i].
- Scurry → /ˈskʌri/, /ˈskɝːi/, /ˈskɜr.i/
Scurry, on the other hand, can be pronounced with /ʌ/, /ɜ/ or /ɝ/, depending on the variety of English:
- the one with /ʌ/ is mostly used in British English
- the one with /ɜ/ can also be found in British English and in some American accents
- the one with /ɝ/ is only found in rhotic accents such as General American
There's a significant acoustic difference between /ʌ/, /ɜ/ and /ɝ/:
- /ʌ/ vs. /ɜ/: The difference between /ʌ/ and /ɜ/ is 'vowel openness' in English; /ʌ/ is a bit more open than /ɜ/. In English, /ʌ/ is usually centralised. Another distinction is that /ʌ/ is usually shorter in length than /ɜ/.
- /ɜ/ vs. /ɝ/: /ɝ/ is called a 'rhotacised' vowel and is mostly found in rhotic accents such as General American. As explained in A course in phonetics by Ladefoged and Johnson, /ɝ/ does not fit on the chart because it can't be described simply in terms of high-low or front-back; it can be said to be r-coloured or a rhotacised vowel. It involves an additional feature called rhotacisation. Rhotacisation describes an auditory property--the r-colouring--of a vowel. Rhotacisation occurs when certain vowels are followed by [ɹ]. R-coloured vowels can be articulated in two distinct ways, depending on the speaker [also from A course in phonetics by Ladefoged and Johnson]:
- some speakers have the tip of the tongue raised, as in a retroflex consonant
- others keep the tip down and produce a high bunched tongue position
Here's a clear illustration of both from A course in phonetics by Ladefoged and Johnson:
/ɜ/, /ɛ/ and /ɝ/ are significantly different vowels. /ɜ/ and /ɝ/ are virtually the same vowel sound; both are central, the only notable difference is that the latter is being influenced by a following [ɹ]. /ɛ/ is a front vowel i.e. the highest point of the tongue is positioned relatively in front in the mouth.
- Don't confuse /ɜ/ and /ɛ/; /ɜ/ is the vowel in 'bird', and /ɛ/ in 'bed'
- The vowel /ʌ/ is the vowel in CUT, TUT, STRUT, HUT, SHUT etc.
- The rhotacised vowel /ɝ/ is only found in rhotic accents of English (chiefly American).
- The rhotacised vowel /ɝ/ is just a vowel, having been strongly influenced by a following R, just like nasalised vowels. Non-rhotic accents such as Southern Standard British English don't have rhotacised vowels.
- The difference between /ˈskɝːi/ and /ˈskɜr.i/ is that the vowel in the former has a rhotacised vowel i.e. it's a vowel, having been controlled by a following [ɹ] while the vowel in the latter is a central vowel followed by a consonant [ɹ].