It will first appear as a small, distant light. Astronomers will turn their telescopes toward the light source. They will not be able to positively identify the object, but many will surmise that it is a natural astronomical phenomenon. Scientists will speculate wildly over the cause of the light source, especially as they notice it growing larger overtime. I think that most people will identify it as a comet on a collision course with earth.
Among all the scientific speculation on the cause of the light source, there are some who will know the cause and meaning of the light source, not because they are privy to secret scientific information or because they are good guessers. They will know the cause of the light source because they read their scriptures and/or the teachings of the prophet Joseph Smith, and they know the signs of the coming of the Lord.
Like the righteous Nephites who knew that the new star in the heavens and the brightness of the sky at the going down of the sun portended the birth of Jesus, the righteous will know that the light in the east is a sign of the coming of the Lord. And like the wicked Nephites who dismissed the new star and extended day as unusual astronomical phenomena with some natural cause, proud scientists will search for naturalistic explanations and call the believers silly.
If all this isn’t weird enough for science, as the light grows in intensity, people will start vanishing from the earth. Two people will be waiting in line at a grocery store and one will suddenly disappear. “Where did she go?” a frustrated clerk will say, pointing to a cart full of frozen food. “She just left her groceries sitting there!” And two people will be working side-by-side at a flour mill when one employee suddenly vanishes. “Where is he now?” a shift supervisor will bark. “Another coffee break!?”
Science will be hard pressed to explain these disappearances. I imagine scholars will be conjuring up theories of spontaneous combustion or being sucked into a subspace portal due to a passing black hole. The righteous will be the only ones being taken from the earth, and they will not fear for they shall know why they are being taken from the earth - to meet the Lord Jesus Christ.
What happens next will be interesting. The atmosphere will get very hot and the earth will begin to burn like an oven. I imagine that proud scholars who mocked the Lord with allusions of flying spaghetti monsters and boasted in their atheistic doctrines of creation will proclaim, as they point toward the large light source, “We were right - It is a comet!” In their final breath, they will be wrong. They will not be burned by a comet; they will be burned by the presence of the Lord and celestialized beings in whose presence they cannot survive.
After the earth is cleansed by fire, the Lord, celestialized beings, and the righteous who were caught up to meet the Lord will arrive upon a renewed, telestialized earth. Thus will begin a thousand years of righteousness and a new era of science that is in complete harmony with the doctrines of the gospel of Jesus Christ.