Alpha (α) in HTML
Alpha is the first Greek letter, written Α and α. The capital is at U+0391 and the small letter at U+03B1.
At a glance
- Character
- Α α
- Named entity
- Α α
- Decimal reference
- Α α
- Hex reference
- Α α
- Unicode code point
- U+0391, U+03B1
- Unicode name
- GREEK CAPITAL LETTER ALPHA, GREEK SMALL LETTER ALPHA
- In the entity reference
- Greek
In detail
The capital alpha is a problem character. It is drawn identically to the Latin capital A in every typeface, but it is a different code point, so a string containing it looks correct and fails every comparison against the Latin spelling. This is the classic confusable, and it is why domain registries restrict mixing scripts within a single label: a name spelled with a Greek capital alpha is a different name that renders the same way.
In graphics, alpha is the transparency channel. The a in an rgba colour or the fourth value in a pixel is alpha, running from fully transparent to fully opaque, and the letter is used because the compositing equations were written with it. That usage is so entrenched that the word alpha on its own in an image tool means opacity rather than the letter.
In statistics, alpha is the significance level, the probability of rejecting a true null hypothesis that you accept in advance. In psychometrics, Cronbach's alpha reports internal consistency of a scale. Neither is the same quantity and both are written with the small letter, so a paper reporting an alpha needs to say which one it means.
In software release naming, alpha is a stage rather than a symbol and is always spelled out in Latin letters. Writing the Greek letter in a version label would be a small act of vandalism against anyone trying to search for it, which is a good general rule: the Greek letter belongs in formulas, the English word belongs in prose.
Examples
<p>Reject the null hypothesis when p < α, with α = 0.05.</p>const latin = "A"; // U+0041
const greek = "\u0391"; // U+0391, drawn identically
latin === greek; // falseThings that catch people out
- Greek capital alpha and Latin capital A are visually identical and never equal. A copied identifier can fail a lookup with no visible reason.
- An alpha value in a colour and an alpha level in a statistical test share a letter and nothing else. Say which you mean.
- The named entities are case sensitive: Α is the capital and α the small letter, and a lowercasing step merges them.
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Related HTML entities
All html entities →Beta (β) in HTML
The Greek letter beta at U+0392 and U+03B2, its entity forms, its meanings in regression and finance, and the German eszett it is mistaken for.
Mu (μ) in HTML
The Greek letter mu at U+039C and U+03BC, its entity forms, the separate micro sign it duplicates, and its meanings in statistics and mechanics.
Sigma (σ) in HTML
The Greek letter sigma at U+03A3 and U+03C3, its entity forms, the summation operator it is confused with, and the final sigma used at the end of a word.
Gamma (γ) in HTML
The Greek letter gamma at U+0393 and U+03B3, its entity forms, what gamma correction actually encodes, and the gamma function that shares the letter.
Delta (δ) in HTML
The Greek letter delta at U+0394 and U+03B4, its entity forms, the increment sign that looks identical, and what a capital delta asserts about a quantity.
Epsilon (ε) in HTML
The Greek letter epsilon at U+0395 and U+03B5, its entity forms, the lunate variant, and what machine epsilon means in floating point comparison.
Tools for this
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