Earthshine is the faint glow on the dark part of a crescent moon, light bounced from the earth onto the moon's surface. The poem opens with a phrase that captures it beautifully: the old moon held in the new moon's arms. It sounds tender, almost like a lullaby, an image of something ancient being cradled by something fresh.
Then comes the swerve. After the dash, the poem gives us "a cellphone set to vibrate." It's a strange, sudden comparison, and it can be read a few ways. The quoted line might be a text message on the screen, or the phone's quiet buzzing might be likened to the moon's hushed glow. Either way, the speaker seems caught between wonder and ordinary modern life.
The mood is quiet and a little wry. The poem doesn't scold technology or simply worship nature. It lets the two sit side by side, suggesting that small, humming everyday objects can share a moment with something as vast as the sky.