According to the writing in the book, Zhuge Liang has been studying Taoism. You can also borrow the east wind, or light a lamp and continue your life. But why the Big Dipper?
Because China has always studied constellations in ancient times. As several stars visible to the naked eye in the night sky, the Big Dipper has become the main research object. Over time, the ancients worshipped the Big Dipper. This seven-star lamp is actually a seven-star array, which corresponds to the Big Dipper in the sky.
It is believed that each star in the seven-star arrangement has a corresponding date of birth. The star corresponding to your birthday is the core monument star of your life. Therefore, in the array, I want to light the core monument lamp of Kong's life.
Moreover, according to the description in the book, Kong Ming had a very complete set of etiquette when he borrowed the life of heaven. We don't know what it is now. However, we should know that most of this is described in the book. In other words, many of them are actually fabricated.
But at the end of the book, Zhuge Liang's last lamp was broken by Wei Yan, so his life extension was not successful. It wouldn't have such a magical effect. Most of what is written in the book is illusory. The Romance of the Three Kingdoms is a novel, not written strictly according to history.
So don't believe these absurd things too much, just know that this is the plot in the novel.