A$.$ How much fuel does the Sun have? The mass of the Sun is $2$ x $1033$ grams. Each gram contains about $6$ x $1023$ hydrogen nuclei. The Sun$$s energy is produced by nuclear reactions in the core of the Sun, from the conversion of four hydrogen nuclei into helium. For each helium nucleus created, $5$ x $10-12$ joules of energy are produced. $($For purposes of an estimate, assume the Sun begins made entirely of hydrogen.$)$ How many joules of energy can the Sun produce in its lifetime? Remember that the Sun can only use half of its hydrogen, and that four hydrogen atoms are used to create each helium atom.