258 a
The CSM Charlie Brown separated from the expanded SIVB third stage housing the LM Snoopy approximately 30 minutes after translunar injection. The crew armed the pyrotechnic devices that first separated the CSM from the SLA (Saturn LM Adapter), and then separated the four SLA panels that had been protecting the stowed LM up until this point. The photograph was taken after the CSM pitched around to examine Snoopy (whose top hatch is clearly visible) before the docking performed by Command Module Pilot John Young. Particles released from the vehicles during separation shine against the blackness of space causing the “firefly” phenomenon.

From the mission transcript after CSM/ SIVB-LM separation:

003:04:00 Public Affairs Office (Mission Control): Apollo 10 is pitching around now, the Guidance Control officers says, pitching around and then will come back in and dock with the Lunar Module. Altitude now 3,580 nautical miles; velocity is down to 25,401.
003:04:23 Cernan: That world is just incredible. There goes a (SLA) panel, Charlie.
003:04:27 Duke (Mission Control): Roger. [...]
003:05:55 Cernan: And the S-IVB ought to be coming in here in a second.
003:05:58 Duke: Roger. Hey, we got the S-IVB coming into the top (on the TV). The sun’s really shining on it. [...]
003:09:44 Cooper (Mission Control): Old Snoopy sure looks good.
003:09:48 Cernan: Yes. He sure do.
003:09:59 Young: Old Charlie Brown is a mass of cord and wire floating around here, though.

258 b
The Earth photographed through the window of the spacecraft with the 80mm lens during jettison of the expanded Saturn SIVB third engine.

“It’s pretty dynamic in those first twelve hours, that’s when things really happen.”
Eugene Cernan (Chaikin, Voices, p. 25)

258 c
The crew took this Hasselblad photograph through the 80mm lens as they were sending a color TV transmission to Mission Control from about 21,000 nautical miles away.


005:04:00 Public Affairs Office (Mission Control): Apollo 10 is going to try to bring up another live color TV show, showing the Earth. We’ll stand by for this transmission. Apollo 10’s distance from the Earth now 21,119 nautical miles. Velocity; 13,170 feet per second.
005:05:27 Cernan: Charlie, if you see this, it’s going to be out of this world, literally. [...]
005:06:54 Stafford: I figure right there you should be able to see the United States, Mexico, Baja California -
005:06:57 Duke (Mission Control): Hey, it’s really beautiful, Tom. It (the TV)’s coming in great.
005:07:01 Stafford: You ought to see it up here, Charlie.
005:07:03 Young: We’ve got the whole globe there. [...]
005:08:10 Stafford: Okay. And it looks like the Rocky Mountains are orange colored to me. The rest of U.S., Baja California, that really stands out as all brownish, and the oceans are blue; but there are so many clouds out to the northeast of the United States, you can’t believe it. Covers the Far East over to Europe as far as you can see.