Final answer:
The Sun is in the main-sequence phase and will stay in this stage for several billion more years before becoming a red giant and eventually transforming into a white dwarf.
Step-by-step explanation:
The stage of development that the Sun is expected to be in is the main-sequence phase. The Sun, having formed about 4.5 billion years ago, is currently in a stable phase of its life, where it has been converting hydrogen into helium through nuclear fusion at its core. This process provides the energy that the Sun radiates into space. It is estimated that the Sun will remain in the main-sequence for several billion more years before it begins to exhaust its hydrogen fuel.
Once the core's hydrogen is depleted, the Sun will undergo dramatic changes, expanding into a red giant. This phase includes the expansion of the Sun’s outer layers and a significant increase in its luminosity. After the red giant phase, the Sun is expected to lose a substantial amount of its mass and expose its hot inner core, forming a planetary nebula. Eventually, the Sun will cool and fade away as a white dwarf over many more billions of years.
The evolution of the Sun will have profound effects on the Earth, including changes in temperature and possibly the end of the planet's ability to support life as the Sun grows larger and hotter in the red giant phase. However, such changes are so far into the future that they do not pose an immediate threat to current life on Earth.