Main Sequence

The following citations listed in this article are from What are Main Sequence Stars? - Universe Guide, Types | Stars - NASA Universe Exploration, and Where on the main sequence are high mass stars? - Wise-Answer.

    After serving time as a Protostar, a star moves onto its next phase: the main sequence. As hinted in the name, stars will spend the majority of their life as main sequence stars (around 90%, to be precise). The stellar population is mostly made up of stars in this stage (also around 90%). This means that said star could spend an estimated 10 billion years before evolving and moving down the cycle; wow, that's a long time! The amount of time a star stays in this cycle depends on its mass. The smaller the star, the slower it uses up its fuel, making this stage longer.

    According to previously cited sources, the main sequence of a star is when "the outward pressure of [a main sequence star's] heat is counter-acted by the inwardly pressure of gravity which keeps the star at a fairly equilibrium." During one's main sequence, a star is ridding itself of mass and energy in order to grow. Think of it like lifting weights; you're exercising to get rid of any unwanted body fat, and by doing so, you're also getting tired and running out of energy (panting, getting sore, etc.). During this phase, a star is, quite literally, bulking up. During its main sequence, a star's job is to convert its hydrogen into helium. Interestingly enough, stars can convert themselves into tons of different elements, depending on their mass. However, a star can never fuse into an element any higher than iron. (Refer to periodic table of elements.)

Image Credits: Free Printable Periodic Tables (PDF)

    When high-mass stars are in their main sequence, they usually appear blue or white, due to their high temperatures. Surprisingly enough, blue actually resembles warmth in space, while red and orange tend to be the colors of cooler stars. Stars with higher masses use up their fuel a lot faster than low-mass stars, which shortens their lives. Take a look at the example of a high-mass star in its main stage below. Its blue hue is extremely vibrant, and if you were to look up at it in the sky, you would probably see a tint of blue in the little dot. High-mass stars are also usually larger in size, so they might appear more luminous.

Image Credits: NASA - Top Story - gamma-ray burst "Rosetta Stone"

    Low-mass stars in their main sequences are also very bright and noticeable. They have lower temperatures and are much smaller in size, but they live longer! As noted before, low-mass stars are usually made up of warmer colors, like yellow or orange. In the image below, this star is actually reaching the end of the main sequence phase, but it still works very well as an example. Personally, I think it kind of looks like a giant fireball!

Image Credits: Life cycle of a White Dwarf - White Dwarf