# Spacing between a special character and text

Why do I get output like this ?

Why is the alignment varying if I embed the special characters like lambda and eta ?

code sample 1:

\begin{gather}
\label{eq:Highest spatial frequency}
\frac{2 \text{ }\eta \text{ }\sin (\alpha )}{\lambda }\\
\shortintertext{where}
\begin{aligned}
&\lambda \text{is the wavelength of the monochromatic light used}\\
&\eta \text{refers to the refractive index of the immersion fluid}\\
&\alpha \text{acceptance angle of the objective}
\end{aligned}\notag
\end{gather}


output:

and ,

code snippet 2:

\begin{gather}
\label{eq:Highest spatial frequency}
\frac{2 \text{ }\eta \text{ }\sin (\alpha )}{\lambda }\\
\shortintertext{where}
\begin{aligned}
&$\lambda$ \text{is the wavelength of the monochromatic light used}\\
&$\eta$ \text{refers to the refractive index of the immersion fluid}\\
&$\alpha$ \text{acceptance angle of the objective}
\end{aligned}\notag
\end{gather}


Output:

• In math mode spacing is determined by TeX. If you want a space you should leave on at within the start and end of the \text{} macro. So it should be \text{ is the wavelength of the monochromatic light used} – Peter Grill Apr 29 '13 at 2:31
• The second example should give you a bunch of error messages as you are already inside a math environment and then switch back to text with $ but then use a math-mode-only command (the Greek letters). The following space (between the second $ and \text) is in fact in text-mode and thus shows up. – Qrrbrbirlbel Apr 29 '13 at 2:44

Spacing in math mode is controlled by TeX. If you want spacing between the math and text you should leave a space within the text{} macro:

## Notes:

• You should not be using \text{ } to add space in math mode. There is a reason why TeX produces the spacing it does in math mode. For instance look at the output produced by $-x-y$, and you will notice a different amount of spacing between the unary "negative" and the binary "minus" operator.

• Not sure how you are getting your second example to compile, as it does not compile for me. One of the reasons why it is always best to post a fully compilable MWE including \documentclass and the appropriate packages.

## Code:

\documentclass{article}
\usepackage{mathtools}

\begin{document}
\begin{gather}
\label{eq:Highest spatial frequency}
\frac{2 \eta \sin (\alpha)}{\lambda }\\
\shortintertext{where}
\begin{aligned}
&\lambda \text{ is the wavelength of the monochromatic light used}\\
&\eta \text{ refers to the refractive index of the immersion fluid}\\
&\alpha \text{ acceptance angle of the objective}
\end{aligned}\notag
\end{gather}
\end{document}

• &\text{$\lambda$ is the ...}\\ is clearer. – egreg Apr 29 '13 at 9:27

Thank you and another way it can be done which I just figured out is the below (by using ~ ) :

\begin{gather}
\label{eq:Highest spatial frequency}
%f_c=\frac{2. \eta \text{ } .(  \text{Sin($\alpha$)})}{\lambda }\\
\frac{2 \text{ }\eta \text{ }\sin (\alpha )}{\lambda }\\
\shortintertext{where}
\begin{aligned}
&\lambda ~\text{is the wavelength of the monochromatic light used}\\
&\eta ~\text{refers to the refractive index of the immersion fluid}\\
&\alpha ~\text{acceptance angle of the objective}
\end{aligned}\notag
\end{gather}


• Don't type 2\text{ }\eta\text{ }\sin: the output is wrong. A thin space will automatically appear between 'eta' and 'sin', but no space is wanted between '2' and 'eta'. – egreg Apr 29 '13 at 9:26