Although there are equivalent third-person formulations using let or may, you do not use an article in a second-person imperative. This is because you are directly addressing someone or something, and so no article is needed — nor allowed.
Therefore you can just say Rise, sun! or Arise, sun!
You can use the so-called vocative particle O before sun to indicate a noun of direct address, as in Rise O Sun! This is sometimes spelled oh, such as Arise, oh sun! But when it has a single letter, O must be capitalized, just as I have done here.
Poetry often uses personification, so a second-person imperative is not uncommon there, even to things not people.
You can go different routes on this, as have many poets before you.
Third-Person Imperatives
Let the Sun Rise
From the musical Hair comes the song “Let the Sunshine In”:
So let the sun shine in, face it with a grin
Smilers never lose and frowners never win
So let the sun shine in, face it with a grin
Open up your heart and let the sun shine in
Or from the lovely anthem “Fly My Pretties" by Angels:
Let the sun rise in the morning,
Let the clouds take on a silver sheen,
and I’ll remember you with each dawning
as you rest in angels wings.
May the Sun Rise
We also have the style of this traditional Irish blessing:
May the road rise up to meet you.
May the wind always be at your back.
May the sun shine warm upon your face,
and rains fall soft upon your fields.
And until we meet again,
May God hold you in the palm of His hand.
Second-Person Imperatives
Rise O Sun
And of course you can switch to second person, as in this translation of the Kalevala:
Rise, oh sun, henceforth and ever,
Still with every morn returning:
Bring a blessing to our homsteads,
To our hunting, to our fishing,
to our planting, to our sowing,
And, at eve, on clouds of crimson,
Rest, reposing as a warrior,
As a hero after battle,
Browned with praises, crowned with honor,
Route thee all the sunset’s glory,
All the grateful earth beneath thee.
Or from the late William Furr’s poem “Rising Sun”:
Rise, oh, sun of God;
Rise up to warm earth’s son.
Men will see you fair
For angels braided your hair.
Rise up, oh, lamp of God;
The heavens will see you plod.
To earth’s four corners you shall shine
As if to warm earth’s kind.
And from the poet William Blake we have this excerpted verse:
Rise up, oh sun! most glorious minister of light and day,
Flow on, ye gentle airs, and bear the voice of my rejoicing.
Wave freshly, you clear water flowers, around the tender grass.
Follow me, oh my flocks! and hear me sing my rapturous song.
Shine Here
Poets have forever addressed the sun in the second person. From John Donne comes this shining example in his poem “The Sun Rising”, in which Donne uses the (archaic) second person throughout when addressing the sun, this time rather vexingly:
Busy old fool, unruly sun,
Why dost thou thus,
Through windows, and through curtains call on us?
Must to thy motions lovers’ seasons run?
Saucy pedantic wretch, go chide
Late school boys and sour prentices,
Go tell court-huntsmen that the king will ride,
Call country ants to harvest offices,
Love, all alike, no season knows nor clime,
Nor hours, days, months, which are the rags of time.
Thy beams, so reverend and strong
Why shouldst thou think?
I could eclipse and cloud them with a wink,
But that I would not lose her sight so long;
If her eyes have not blinded thine,
Look, and to-morrow late, tell me,
Whether both th’ Indias of spice and mine
Be where thou leftst them, or lie here with me.
Ask for those kings whom thou saw'st yesterday,
And thou shalt hear, ‘All here in one bed lay.’
She’s all states, and all princes, I,
Nothing else is.
Princes do but play us; compared to this,
All honour’s mimic, all wealth alchemy.
Thou, sun, art half as happy as we,
In that the world’s contracted thus.
Thine age asks ease, and since thy duties be
To warm the world, that’s done in warming us.
Shine here to us, and thou art everywhere;
This bed thy center is, these walls, thy sphere.
Apparently Donne was not so pleased with the sun’s rising, reversing the psalmist’s famous reflection of Psalms 30:5 that
Weeping may endure for the night,
But a shout of joy cometh in the morning.
Donne inverts the psalmist, instead taking his delight by night and lamenting the morn.