Rails - Get the current week's and month's start and end dates

I am new to ruby on rails and got stuck in dates. I used Time.now to get the current time. Now I want to find out the srart and end dates for the current week and current month. For instance:

If Time.now returns me -

2012-08-13 15:25:35 +0530

Then the start and end dates for the current week are:

2012-08-12 - 2012-08-18

Then the start and end dates for the current month are:

2012--08-01 - 2012-08-31

I am implementing the same using the code:

Time.now.wday   
 => 1 

Time.now - 1.day
=> 2012-08-12 15:31:44 +0530 

Time.now + 5.day
 => 2012-08-19 15:32:38 +0530

and so on.. But I dont find it a convenient way to do this. Iam sure Ruby on Rails does hold a better solution. Can anyone suggest to figure out the same..