Here's a breakdown:

Temperature:

* Spectral type: Stars are classified into spectral types based on their surface temperature. The classification system uses letters O, B, A, F, G, K, and M, with O being the hottest and M being the coolest.

* O: > 30,000 K (blue)

* B: 10,000 - 30,000 K (blue-white)

* A: 7,500 - 10,000 K (white)

* F: 6,000 - 7,500 K (yellow-white)

* G: 5,000 - 6,000 K (yellow) - Our Sun is a G-type star

* K: 3,500 - 5,000 K (orange)

* M: < 3,500 K (red)

* Color: The color of a star also indicates its temperature. Hotter stars appear blue, while cooler stars appear red.

Brightness:

* Absolute magnitude: This is a measure of a star's intrinsic brightness, or how much light it actually emits. It's defined as the apparent magnitude a star would have if it were located 10 parsecs (32.6 light-years) away.

* Lower absolute magnitude: A star with a lower absolute magnitude is brighter.

* Higher absolute magnitude: A star with a higher absolute magnitude is fainter.

Important Note: While spectral type and absolute magnitude are the primary indicators, other factors can affect how a star appears to us. These include:

* Distance: Stars that are closer appear brighter than those that are farther away.

* Interstellar dust: Dust clouds can absorb or scatter starlight, making stars appear fainter.

Let me know if you'd like a more detailed explanation of any of these concepts!