ExhausTeD

I have many thing I am trying to improve in my life. Current Focus: Physics, Astronomy and Math. Next Focus: Programming in Python

[slinkybun]

What is our galaxy? How do we know where we are located within it?

The term galaxy refers to an immense collection of stars and interstellar matter, far larger than a star cluster, with typically 10^11 - 10^12 stars. Our Milky Way Galaxy doesn't just contain stars, but also copious interstellar dust. This dust obscures the Galaxy's true dimensions (called interstellar extinction, makes distant objects appear dim).

Our sun is located in the disk of our Milky Way Galaxy about 8,000 pc from the galactic center. This was found using the globular clusters above our Milky Way Galaxy's disk plane. By finding our distance from them as we move using pulsating variable stars like Cepheids and RR Lyrae, we could find the general location of the galaxtic center. Being ablbe to find the distance between us and RR Lyrae was incredibly important, as they are found abundantly in globular clusters of stars.

Globular Clusters are found spread along the the Milky Way and their distributions were three-dimensionally mapped to show us that they form a huge spherical distribution centered not on the Earth, but rather about a point in the Milky Way several kiloparsecs away in the direction of Sagittarius. This point must coincide with the center of the Galaxy.

The Formula for finding the distances of stars:

[slinkybun]

Wave Optics:

The speed of a wave (c) Refractive index (n) Wavelength (λ) Frequency (𝑓) c= 3*10^8 m/s c= 𝑓λ v= c/n = 𝑓λ/n

When light moves from one medium into another, its frequency stays the same, while both the speed and wavelength generally change. Example Problem 1:

Orange light of wavelength λ = 600 nm in air enters water having an index of refraction of 𝑛 = 1.33. (a) What is the frequency of this light? (b) What is the speed of the light in the water? (c) What is the wavelength of the light in the water? (d) If you were swimming underwater and looked at this light, what color would you see?

(a) 𝑓= c/λ = 3*10^8 / 600*10^-9 = 5*10^14 (b) v= c/n = 3*10^8 / 1.33 = 2.26*10^8 (c) 𝑓= c/λ => 2.26*10^8 = (5*10^14) λ => λ= 4.52*10^-7 m= 452 nm (d) Trick question. Red, because human eyes pick up on frequency under water. The plane in which the electric field oscillates is called the plane of polarization.

The intensity 𝐼 of a beam of light is the energy per second per square meter carried by the light. It turns out that the intensity is proportional to the square of the electric field amplitude.

We can measure the intensity of a beam of light.

To double the intensity of an electromagnetic wave, you should increase the amplitude of the electric field by a factor of 1.414.

Light waves can be manipulated to control the orientation of the electric field vector. Most light is unpolarized – electric field vectors point randomly in all directions. A polarizer transmits only one component of the electric field vector to create light that is linearly polarized – the electric field is constrained to one plane.

A polarizer allows transmission of the electric field component parallel to its axis. Consider light that has an electric field of amplitude 𝐸0. Then if the polarizer axis is at angle 𝜃 with respect to the electric field, the transmitted electric field amplitude is: 𝐸(𝜃) = 𝐸0 cos 𝜃 The transmitted intensity 𝐼 (proportional to 𝐸^2) is 𝐼 = 𝐼0 cos^2 𝜃 where 𝐼0 is the incident wave intensity in watts per square meter. (W/m^2)