Our mornings belong to Phosphor

Hesper and Phosphor are the names the Greeks gave to the Evening Star and Morning Star. We now know, of course, that both are the planet Venus, the brightest object in the sky after the Sun and Moon. Because Venus circles the Sun on a smaller orbit than ours, we always see the planet near the Sun, to one side or the other, catching it in darkness just after the Sun has set, or just before the Sun rises.

But you know this.

As the year begins Venus is high in the east at sunrise. Now it will slowly slide towards the Sun, by midyear disappearing into the dawn, reappearing in the evening sky late in the year.

In In Memoriam, Tennyson addresses Venus in both her guises. First as the Evening Star:

Sad Hesper o'er the buried sun
          And ready thou, to die with him,
          Thou watchest all things ever dim
And dimmer, and a glory done.

Then as the Morning Star:

Bright Phosphor, fresher for the night,
          By thee the world's great work is heard
          Beginning, and the wakeful bird;
Behind thee comes the greater light.

I slip in pre-dawn darkness onto the terrace. Ah, Phosphor. Wakeful beauty. You and I fresher for the night. Wait now, wait, coffee mug in hand, as the sky simmers into violet, pink and gold, until at last gleaming Phosphor dissolves in the star's greater light.

Who was the first to guess that Hesper and Phosphor are one?

Sweet Hesper-Phosphor, double name
          For what is one, the first, the last,
          Thou, like my present and my past,
Thy place is changed; thou are the same.