The poem opens with calm and serene note totally contrary to the horror that comes the next moment. This ironical opening is to create a strong sense of disturbance or loss that the explosion causes.

The opening of the poem is the total opposite of what is going to happen in the next few minutes. The poet says that it is a calm, beautiful and warm morning i.e. a pleasant weather. But suddenly a flash appears due to the nuclear bomb explosion which changes the whole weather and the atmosphere.