Searching for a variable (=previously defined pattern) using grep

Question

I'd like to create a bash script. Therefore, I defined a variable

pattern1=Today,\ 15:46

I had to add a \ before the space " " because otherwise I get the error "command not found"

Now, I used this command to search the pattern in out.txt:

grep -c '$pattern1' out.txt

Here grep doesn't find anything.

However, when I type in

grep -c 'Today, 15:46' out.txt

I get a result.

Also with the following code, I don't get any result:

define pattern2=15:46
grep -c '$pattern2$ out.txt

Where is the mistake? Can grep not look for a previously defined pattern? Is there a trick to look for the pattern anyway?

I'd be grateful for every help!

Kind regards, X3nion