On December 25, 1968, after 10 revolutions around the Moon, Apollo 8’s SPS (Service Propulsion System) engine was successfully ignited over the farside for trans-Earth insertion (TEI) to accelerate out of lunar orbit. An engine failure would have stranded the men in lunar orbit with no hope of rescue but all went well to the relief of the crew.

This superb and very rare photograph was taken by William Anders with the 250mm telephoto lens as the spacecraft was gaining altitude following trans Earth ignition. Features of both the lunar nearside and farside from a perspective not visible from Earth. Smyth’s Sea is at the bottom center, the Sea of Crises at the top left and the bright ray Crater Giordano Bruno with the dark-floored Crater Lomonosov are at the top right.

“We were there [in lunar orbit]. I mean, if things didn’t work going t≈o the Moon, we were going to get a free ride home, on a free-return trajectory. Maybe the reentry wouldn’t be perfect, but at least we’d have a shot at it. Once that rocket worked and got us to lunar orbit, then it had to work again, or we were stuck.”

—William Anders (Chaikin, Voices, pg. 42)

From the mission transcript after acquisition of signal with Earth
following the successful trans Earth ignition over the lunar farside:

089:34:16 Lovell:

Houston, Apollo 8, over.

089:34:19 Mattingly (Mission Control):

Hello, Apollo 8. Loud and clear.

089:34:25 Lovell:

Roger. Please be informed there is a Santa Claus.

089:34:31 Mattingly:

That's affirmative. You're the best ones to know.

089:34:37 Lovell:

And burn status report: it burned on time; Burn time, 2 minutes, 23 seconds; seven-tenths plus VGX. Attitude nominal, residuals; minus five-tenths VGX, plus four-tenths VGY, minus 0 VGZ; Delta-VC, minus 26.4.

089:35:14 Mattingly:

Roger.

089:35:19 Mattingly:

Apollo Flight has...

089:35:23 Mattingly:

Apollo 8, recomfirm your burn time, please.

089:35:30 Lovell:

Roger. We had 2 minutes, 23 seconds. Our - wait one. Stand corrected to that; 3 minutes, 23 seconds.

089:35:43 Mattingly:

Thank you. [Long pause.] This is Mission Control, Houston. Flight Dynamics Officer says that burn is good.

089:36:33 Borman:

You get the sensation that you're climbing, Ken.

089:36:35 Mattingly:

Say again, Apollo 8.

089:36:41 Borman:

I say, this gives you the sensation that you're climbing.

089:36:47 Mattingly:

Rog.