Generating true random numbers

this is my first post on StackOverflow, so just tell me if I made something wrong :)

In my cryptography lessons i learned that one should use as many parameters together as possible in order to have the entropy to generate a close to perfect random number. My question is: Let's say I would just messure the temperature of room at a given moment (e.g. 19,6573°C), would the number not be already random enough? I mean an attacker could not possibly guess my room temperature and he could also not messure it afterwards, because he would need to go back in time^^

Since cryptographic algorithms would turn my temperature from 19,6573 to a string of 512 characters or more and an attacker would not be able to reproduce the messurement, my random number should be random enough, or not?