Well... It's a some-what long process involving the Underground. First, you need to have at least ten Red Shards. These can be dug up in the Underground. Go to Route 212, and there will be a house there. A lady will give you a TM for every 10 shards of the same color. Sunny Day for Red, Rain Dance for Blue, Hail for Green, and Sandstorm for Yellow.
use a TM
By using Sunny day, Hail, Rain Dance. Moves that It can learn
Well, it's pretty hard but try migrating Pokemon that has a move Sunny Day from Pokemon Fire red, Leaf green, Ruby, Sapphire and Emerald. Or just trade with a friend with that move. Forgive this answer. Though I've played this game 4 times with different Pokemon I forget where to find it.
TM11 Sunny Day can be found in the Safari Zone.
Once a a day in Pokemon Platinum
use a TM
You have to use sunny day in a battle, and then it will go back to normal after sunny day ends or you end the battle.
By using Sunny day, Hail, Rain Dance. Moves that It can learn
gym leader
The eighth gym leader in Pokemon platinum is the one in sunny shore city.
If sunny ville is Sunyshore City, you have to obtain giratina, and get the all of the other gym badges.
Well, it's pretty hard but try migrating Pokemon that has a move Sunny Day from Pokemon Fire red, Leaf green, Ruby, Sapphire and Emerald. Or just trade with a friend with that move. Forgive this answer. Though I've played this game 4 times with different Pokemon I forget where to find it.
TM11 Sunny Day can be found in the Safari Zone.
That move would be Sunny Day.
surf north off of Sunny shore city
Not were, but where, the day care in Pokemon platinum is in solaceon town which northeast of hearthome city
You don't need an item for it. You need to have sunny weather in the game for it. There are two ways to get sunny weather. They are: A. Get a Pokemon that learns the Sunny Day move B. Send Groudon out into battle, which has the ability drought so it makes sunlight happen