they all refer to "groundhogs day" in USA. It is a regional thing, in the pennsylvania area. So in my opinion, don't bother to learn the significance because nobody else knows about this stuff accept for a minority of americans who are from this region.
is the official website . or just google groundhogs day.
it is an annual event which occurs in punxutawney, PA. Punxutawney is an "indian" term, it is not English. For this event, government officials dress up in historic costumes to watch an animal , a groundhog (which is considered a "marmot," the squirrel family) come out of it burrow.
Once out, this creature cast a shadow, which people consider to be a prediction ( a "prognosis" hence pronoshocgation rhyming with prognosis and punxutawney/ "marmot proposition" is a play on "mammouth proportions" / "protention of light and shadow" is reference to sunlight casting shadow of the groundhog, but I believe protention is misspelled. it's probably "portentous" or "portension")
anyways, the groundhog's shadow is suppose to be a prediction of a longer winter. The absence of a shadow indicates an early spring. Hence the significance of the event.
It's totally stupid, hence to foolish puns.
there's a movie with Bill Murray in it, called "groundhogs day." So maybe you can watch it and train your english listening skills