[Tex/LaTex] How to embed plain text into math mode

amsmathmath-modetext;

I really don't understand what's the problem with this piece of code: 

\documentclass[a4paper,11pt]{article}

\usepackage{amsmath} % declares a predefined package for math

\begin{document} %starts document

\begin{align} %starts a formula block
\text{Number of looks in\newline azimuth direction 
    &= \frac{\text{Pixel spacing slant range}}{\text{Pixel spacing azimuth}}\times \sin (\text{Incidence angle})}\\
    &= \frac{9.3685143}{3.5448059\times \sin (23.871\circ)}
\end{align} %ends formula block

\end{document} %ends document

When I try to build and run, I get a bunch of errors, including: 

line 11: Misplaced alignment tab character &. \end{align}
line 11: Missing $ inserted. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Misplaced alignment tab character &. \end{align}
line 11: Missing $ inserted. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Misplaced alignment tab character &. \end{align}
line 11: Missing $ inserted. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Misplaced alignment tab character &. \end{align}
line 11: Missing $ inserted. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Misplaced alignment tab character &. \end{align}
line 11: Misplaced \omit. \end{align}
line 11: Misplaced \cr. \end{align}
line 11: Misplaced \noalign. \end{align}
line 11: Missing $ inserted. \end{align}
line 11: Missing } inserted. \end{align}
line 11: Missing } inserted. \end{align}
line 11: Missing } inserted. \end{align}
line 11: Missing } inserted. \end{align}
line 11: Missing $ inserted. \end{align}
line 11: Missing } inserted. \end{align}
line 11: Missing } inserted. \end{align}
line 11: Missing } inserted. \end{align}
line 11: Missing } inserted. \end{align}
line 11: Missing $ inserted. \end{align}
line 11: Missing } inserted. \end{align}
line 11: Missing } inserted. \end{align}
line 11: Missing } inserted. \end{align}
line 11: Missing } inserted. \end{align}
line 11: Missing $ inserted. \end{align}
line 11: Missing } inserted. \end{align}
line 11: Missing } inserted. \end{align}
line 11: Missing } inserted. \end{align}
line 11: Missing } inserted. \end{align}
line 11: Missing $ inserted. \end{align}
line 11: Missing } inserted. \end{align}
line 11: Missing { inserted. \end{align}
line 11: Missing } inserted. \end{align}
line 11: Missing { inserted. \end{align}
line 11: Missing } inserted. \end{align}
line 11: Missing { inserted. \end{align}
line 11: Missing } inserted. \end{align}
line 11: Missing } inserted. \end{align}
line 11: Missing } inserted. \end{align}
line 11: Missing } inserted. \end{align}
line 11: Missing } inserted. \end{align}
line 11: Missing \cr inserted. \end{align}
line 11: Missing { inserted. \end{align}
line 11: Missing { inserted. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Missing $ inserted. \end{align}
line 11: Missing } inserted. \end{align}
line 11: Misplaced alignment tab character &. \end{align}
line 11: Misplaced \omit. \end{align}
line 11: Misplaced \cr. \end{align}
line 11: Misplaced \cr. \end{align}
line 11: Extra }, or forgotten \endgroup. \end{align}
line 11: Extra }, or forgotten \endgroup. \end{align}
line 11: Missing number, treated as zero. \end{align}
line 11: Illegal unit of measure (pt inserted). \end{align}
line 11: Missing number, treated as zero. \end{align}
line 11: Illegal unit of measure (pt inserted). \end{align}
line 11: Improper \halign inside $$'s. \end{align}
line 11: Misplaced alignment tab character &. \end{align}
line 11: Missing $ inserted. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Misplaced alignment tab character &. \end{align}
line 11: Missing $ inserted. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Misplaced alignment tab character &. \end{align}
line 11: Missing $ inserted. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Misplaced alignment tab character &. \end{align}
line 11: Missing $ inserted. \end{align}
line 11: Extra }, or forgotten $. \end{align}
line 11: Extra }, or forgotten $. \end{align}

As you know, line 11 is: \end{align}

Best Answer

Probably you like to achieve this:

enter image description here

Instead of \text in first occasion you should use \parbox which enable to write two line text. After than you need to clean-up remedy with curly braces:

\begin{document} %starts document

\begin{align} %starts a formula block
\parbox{8.5em}{Number of looks in\\ azimuth direction}
    &= \frac{\text{Pixel spacing slant range}}
            {\text{Pixel spacing azimuth}}\times \sin (\text{Incidence angle})\\
    &= \frac{9.3685143}{3.5448059\times \sin (23.871^\circ)}
\end{align} %ends formula block

\end{document}

Addendum: Considering Andrew Swann comment, use siunitx for units and make text width a bit wider with geometry package I obtain:

enter image description here

\documentclass[a4paper,11pt]{article}
\usepackage[showframe]{geometry} % show page layout and make text width wider ...
                                 % in final use option "showframe" had to be removed
\usepackage{amsmath} % declares a predefined package for math
\usepackage{siunitx}

\begin{document} %starts document

\begin{align} %starts a formula block
\parbox{8.3em}{\centering Number of looks in\\ azimuth direction}
    &= \frac{\text{Pixel spacing slant range}}
            {\text{Pixel spacing azimuth}\times \sin (\text{Incidence angle})}\\[1ex]
    &= \frac{9.3685143}{3.5448059\times \sin (\SI{23.871}{\degree})}
\end{align} %ends formula block

\end{document}

Edit: It seems that factor \sin{...} had to be in the denominator. I correct this my misunderstanding of given MWE. Above mine MWE and image of equation is now corrected.

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