Matthew Poole and continuators on Psalms 89:37

37 It shall be established for ever as the moon, and as a faithful witness in heaven . Selah.

Whereby he understands either first the moon last mentioned, to which this clause may be added rather than to the Sun, to imply that as the Moon, though subject to Eclipses and frequent and manifold changes, yet doth constantly and perpetually remain in Heaven; as a witness of my covenant of the night, as it is called Ier. 33. 20. so shall the House and Kingdom of David continue for ever notwithstanding all the Changes and Calamities which it may undergo. Or secondly the Rainbow, which though in it self it be unstable and transient, and doth but seldom appear, which learned men object against this opinion, yet in Scripture is mentioned as Gods faithful and perpetual witness, being called a token of Gods everlasting covenant between God and every living creature for perpetual generations, Gen. 9. 12, 16. And although it do not always appear to us, neither do the Sun or Moon do so, yet its appearances are doubtless very frequent in one or other part of the World, and will be repeated from time to time to the end of the World. Add to this that the word here rendred Heaven, may as well be rendred the Cloud or Clouds, as it is used Deut. 33. 26. Iob 35. 5. and 36. 28. Psal. 18. 12. and 77. 17. and 78. 23. Prov. 3. 20. Isa. 45. 8. And so the place being thus translated, and as the faithful witness in the Cloud or Clouds, doth plainly point us to the Rainbow.