On Jan. 5, the rocket stage passed less than 6,000 miles from the moon. The moon’s gravity swung it on a course that looked like it might later cross paths with the moon.
Mr. Gray put out a request to amateur astronomers to take a look when the object zipped past Earth last week.
One of the people who answered the call was Peter Birtwhistle, a retired information technology professional who lives about 50 miles west of London. On Thursday last week, the domed 16-inch telescope in his garden, grandly named the Great Shefford Observatory, pointed at the part of the sky where the rocket stage zipped past in a few minutes.
“This thing’s moving pretty fast,” Mr. Birtwhistle said.
The observations pinned down the trajectory enough to predict an impact. Astronomers will have a chance to take one more look next month before the rocket stage swings out beyond the moon one last time. It should then come in to hit the far side of the moon, out of sight of anyone from Earth.
NASA’s Lunar Reconnaissance Orbiter will not be in a position to see the impact live. But it will later pass over the expected impact site and take photographs of the freshly excavated crater.
Mark Robinson, a professor of earth and space exploration at Arizona State University who serves as the principal investigator for the Lunar Reconnaissance Orbiter’s camera, said he expected four tons of metal, hitting at a speed of some 5,700 miles per hour, would carve out a divot 10 to 20 meters wide, or up to 65 feet in diameter.
That will give a scientists a look at what lies below the surface, and unlike meteor strikes, they will know exactly the size and time of the impact.
