It is incorrect to call the Lunar Calendar as Islamic and the Solar Calendar as Christian.
13:2 God is the One Who raised the skies without pillars visible to you. Then, upon the Throne of His Almightiness, He assumed Supreme Control of the entire Universe. He committed the sun and the moon to be of service, each running to an appointed term. He keeps Order in the Universe and He explains His Messages in detail, so that you may be sure of meeting with your Lord. [Studying the Book of Nature will bring mankind closer to their Lord. The sun was thought to be stationary, but today we know that the sun, along with Solar System, is moving toward the "Constellation of Hercules," also known as the "Solar Apex", at a speed of 12 miles per second, 43,200 miles per hour. 36:38]
55:5 The sun and the moon run by a mathematical design. [Such are the changeless Divine Laws]