Why is there no line yet for today in the burndown chart?

If nothing has happened yet today, and it is before noon, the burndown chart does not yet show any line for today. This is because the line would be flat, and would make it look like you are already behind in the project from the morning. So, the burndown chart doesn't show a line for today until something has happened today that affects the burndown chart - like a task being completed - or it is past noon (in the local time zone of the team or sprint).