It is often necessary to insert special symbols in a scientific presentation. Most of the special characters you’ll need can be found buried the “Edit — Special Characters…” dialog within Keynote, but it’s annoying to do this every time you want to insert a ⊙. Thankfully, you can set up simple shortcuts in Keynote using the “Auto-Correction” feature in the Preferences Panel (⌘-,), allowing a LaTeX-like interpretation of special characters.
To do this, open the Keynote Preferences and click on the “Auto-Correction” tab. Some default characters will probably already be there. Add a new auto-correction string by clicking the “+” icon at lower left. Set the “Replace” string to something like \lambda and the “With” string to the symbol you want to replace it with, in this case α. Some useful characters are provided below that you should be able to copy and paste directly into the Auto-correction Preferences dialog.
Ω Λ Δ Σ α β γ δ ε ζ η θ ι κ λ μ ν ξ ο π ρ σ τ φ χ ψ ω
⊙ Å ≤ ≥ ≠ × ∫ ∑ ∆ ∞ ∝ −
For characters not included here, you’ll have to navigate through the (searchable) “Special Characters…” dialog.
An example slide is shown below, typed as
The sun has a mass of 1 M (ctrl + ⌘ + -) \odot H\alpha emission is observed at \lambda = 6563 \AA
Note that the text above also looks like normal LaTeX output, because it is written in the “Computer Modern” font, which is the LaTeX default. The font can be downloaded HERE in a format such that you can use it in OSX-native applications like Keynote or Pages. To install the font, simply drag all of the “.otf” files extracted from the distribution tarball into the “Font Book” application.