Final answer:
Astronauts during Apollo missions, including Jim Lovell during Apollo 13, used various navigational aids such as the Earth, onboard computers, navigational tools, and communication with ground control for guidance during their journey.
Step-by-step explanation:
The question references Jim Lovell who was the astronaut in command of the Apollo 13 mission. A significant part of Lovell's role was to guide the Lunar Excursion Module (LEM). Although the question does not specify the exact point of reference Lovell used during the short engine burn to lead the LEM, it is known that astronauts of the Apollo missions used a variety of navigational aids. One of the commonly used points of reference in such cases is the Earth. They also used intricate navigational tools and techniques, including charts, onboard computers, and communication with ground control at Houston. Thus, Earth, navigational tools, and support from ground control have likely been used as reference points during the journey.
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