Analysis of Snow or Snowdrops?

Is it snow or snowdrops' shimmer
Whitens thus the bladed grass,
With a faint aërial glimmer,--
Spring or winter, which did pass?
For the sky is dim and tender
With an evanescent light,
And the fading fields are white,
White with snow or snowdrops, under
The fair firstling stars of night.

Little robin, softly, cheerly
Piping on yon wintry bough,
Why have all the fields that pearly
Iridescence, knowest thou?
Did old Winter, grim and hoary,
Aim a parting dart at Spring
As she fled on azure wing,
Or did she with rainbow glory
In his face her snowdrops fling?