The phases of Venus are similar to those exhibited by the Moon, and are caused by a change in position of the illumined hemisphere of the planet with regard to the Earth. At superior conjunction the whole enlightened disc of the planet is turned towards the Earth, but is invisible by being lost in the Sun’s rays. Shortly before or after it arrives at this point, its form is gibbous, the illumined portion being less than a circle but greater than a semi-circle. At its greatest elongation west or east of the Sun the planet resembles the Moon in quadrature—a half moon—and between those points and inferior conjunction it is visible as a beautiful crescent. It becomes narrower and sharper as it approaches inferior conjunction, until it resembles a curved luminous thread prior to its disappearance at the conjunction. After having passed this point it reappears on the other side of the Sun as the morning star.
It would be only natural to imagine that this peerless orb, the most beautiful and lustrous of the planets, upon which men have gazed with longing admiration, and designated the emblem of ‘all beauty and all love,’ should have impressed Milton’s poetical imagination with its charming appearance, and stimulated the flow of his captivating muse. He addresses the orb as
Fairest of Stars, last in the train of night,
If better thou belong not to the dawn,
Sure pledge of day, that crown’st the smiling morn
With thy bright circlet, praise Him in thy sphere
While day arises, that sweet hour of prime.—v. 166-70.
In these lines the poet alludes to Venus as the morning star.
In the other passages in his poem Milton associates the planet sometimes with the morning and at other times with the evening—
His countenance, as the Morning Star that guides
The starry flock.—v. 708-709.
Or if the Star of Evening and the Moon
Haste to thy audience, Night with her will bring
Silence, and Sleep listening to thee will watch.—vii. 104-106.
And hence the morning planet gilds her horns.—vii. 366.
The Sun was sunk and after him the Star
Of Hesperus, whose office is to bring
Twilight upon the Earth, short arbiter
Twixt day and night.—ix. 47-50.
and bid haste the Evening Star
On his hill top to light the bridal lamp.—viii. 519-20.