Jeff walks us through a way to weigh a black hole in program 1.

I loved the magazine "Popular Mechanics" because it was full of gadgets and gizmos. When I was about 11, a tiny ad for a powerful 100X telescope caught my eye. I sent in my dollar and they sent me two lenses with the instructions that I was to hold them 7 feet apart and look in the small one. Eventually I managed this by mounting them in a long cardboard tube that linoleum is rolled onto. I remember my double astonishment when I first looked at the neon sign of a car dealer on the other side of the bay, a mile away: "It's upside down! I can read it!" And the moon looked as close and real as the rock quarry across the bay. These were personal discoveries--as exciting as any that I have experienced.

Weighing a black hole depends on laws formulated by Kepler and Newton centuries ago.

In the next 3-4 years I polished a telescope mirror and built two telescopes--a 6-inch reflector and a 4-inch refractor. One day, when I was about 14, I read an astounding article in the Seattle newspaper about a small, personal observatory in Kirkland, WA that had been struck and penetrated by a meteorite! As soon as I possibly could, I called the owner; he answered with these words: "This is Hawthorne at the Pearly Gates." I arranged to make the three-hour ferry and bus trip to visit him on the following weekend. Mr. Hawthorne, a diabetic who was missing both a hand and a foot, was in his nineties. Right away he showed me the meteorite, the rip in the aluminum dome, and the final impact point near the base of the telescope.

In the red circle, A0620's visible companion star: you need to figure out its period to calculate the mass of the black hole.

I made several visits to Mr. Hawthorne's place. He had a wealth of equipment and know-how and he helped me machine telescope parts. Watching steel being cut, as though it were balsa wood being whittled with a knife, was very exciting to me. There are many other experiences I can recall, but perhaps none was more exciting and unexpected than Mr. Hawthorne's abilities as a calligrapher. I did not know what calligraphy was, and one day he pulled a double-nibbed pen out of his desk, dipped it in some ink and wrote my name in big, bold script about a dozen times. I guess he wrote so fast that the tremor in his hand scarcely affected the result, which was magnificent. I'm happy to say that the nameplate on my office door today is a photograph of one sample of this ornamental penmanship that Mr. Hawthorne did for me about 45 years ago.