O Oriens

O Morning Star,
splendour of light eternal and sun of righteousness:
Come and enlighten those who dwell in darkness
and the shadow of death.

cf Malachi 4.2

This does seem especially appropriate for solstice. In the Northern hemisphere, from here on the days get longer again.

My favourite part of Morning Prayer, incidentally, is this:
In the tender compassion of our God •
the dawn from on high shall break upon us,

To shine on those who dwell in darkness and the shadow of death, •
and to guide our feet into the way of peace.

These antiphons don't belong in Morning Prayer -- they're an Evening Prayer thing, sandwiched around the Magnificat. But this one reminds me of morning prayer, and the just-before-dawn, forward-looking feel of much of the liturgy around this time.