(M=20 Suns, R=1,000 Suns, L=135,000 Suns, T=3,500 K, d= 600 l.y., Age = 8.5 million years)

PROPERTIES OF STARS

---

Properties of Typical Main Sequence Stars M* = 0.08 to ~50-100 MSun R* = 0.1 to ~103 RSun T* = 2,500 K to 50,000-100,000 K* L* = 10-4 to 105 LSun

Properties of the Sun (Solar Units) MSun = 2.0x1030 kg RSun = 7.0x105 km TSun = 5,800 K LSun = 3.9x1023 kW

Properties of the Earth ME = 3.0x10-6 MSun RE = 9.2x10-3 RSun TE = 283-288 K ~ 50-60 Farenheit LE ~ 1.8x1014 kW

The range in properties is large^*, however, in a certain sense, it is interesting that the range is actually as small as it is. Clumps of matter in the Universe range from objects as small or smaller than nuclei of atoms, masses on the order of 10^-27 kg and diameters on the order of 10^-15 meter, to structures on the scale of the Universe itself which is larger than tens of billions of light years across.

---

^* Powers of Ten and newer version BBC Powers of Ten

---

Question: How are these numbers are determined?

• masses--from the standpoint of stars, the mass is the most important property about which we want to garner information. Of the properties listed, mass, radius, luminosity, surface temperature, the mass is the quantity which changes least over the star's lifetime. Consequently, knowing only the mass of a star, we can tell you about how the star will spend its lifetime and what it will look like at various different stages of its life. Despite the importance of the stellar mass, there are only dozens of direct, precise determinations of the masses of massive stars. The most reliable masses come from observations of binary star systems.

• radii--Only a handful of direct measurements of stellar radii exist (fewer than 1,000) most coming from observations of binary star systems.

• surface temperatures--for now we consider what is known as the the color temperature, quantity based on the star's continuous spectrum. Next lecture, we return to temperatures and discuss what is known as the line temperature , the temperature based on the absorption lines observed in a star's spectrum. There are several ways to find surface temperatures of stars and, in fact, it is fairly straightforward to find surface temperatures of stars.

• luminosities--knowing the luminosity of a star is important because it tells how powerful is gthe star. the hardest part of finding luminosities for stars (and, in fact, for any Celestial object) is finding how far away is the star. The difficulty of finding distances to objects is a recurring theme in all branches of astrophysics.

---

---