Speed of Light: How Does Light Travel? 

300,000 km is right, but in physics it must be in metres unless otherwise asked for.

By using parallax (the angle size relative to the rotating motion of the earth) or ,in some cases, spectra, where the location of specific thing on a spectrum indicates the distance of an object or whether or not it's moving away.

@@gr8withan8playz fantastic answer but you completely avoided the question. So using the parallax and angles how do we know what effects dark matter has on the readings if we dont know what it is or how things react to it. You know if dark matter supposedly makes up 85% of the universe. That's a very large % to not know anything about but still thing normal physics laws apply?? Now if it doesn't exist then science has no idea what holds galaxies together. So you still haven't answered the question. Really because you cant. Neither can science or me. No one can because no one knows what dark matter is lol. This means that the while giant 13.5 billion light year across universe could be very small. I cant prove it's small but science cant prove it's big. But what they did prove is that they have to make up some invisible stuff, that we cant test or measure, to allow the gravitational orbital mechanics that holds galaxies together to work. Here is what wikipedia says about: Dark Matter - Dark matter is a form of matter that is thought to account for approximately 85% of the matter in the universe and about a quarter of its total energy density. The majority of dark matter is thought to be non-baryonic in nature, possibly being composed of some as-yet undiscovered subatomic particles.[note 1]Its presence is implied in a variety of astrophysical observations, including gravitational effects that cannot be explained by accepted theories of gravity unless more matter is present than can be seen. For this reason, most experts think dark matter to be abundant in the universe and to have had a strong influence on its structure and evolution. Dark matter is called dark because it does not appear to interact with observable electromagnetic radiation, such as light, and is thus invisible to the entire electromagnetic spectrum, making it extremely difficult to detect using usual astronomical equipment.

f00zh wow

That’s not scientific math

A magnet has potential attraction or repulsion energy. Light is electromagnetic propagation... therefore without mass it has energy..

@@SirPoopDollar Propagation of an ElectromagneticWave. Electromagnetic waves are waves which can travel through the vacuum of outer space. ... Thepropagation of an electromagneticwave through a material medium occurs at a net speed which is less than 3.00 x 108 m/s. So if this is true then how can we use light as a tool for measurement? How can anyone say with any certainty that things are light years away when we dont know everything that light traveled thru to get to us. Because space is a vacuum that's not empty, dark matter and all the other stuff science doesn't understand. And then once light has slowed down going thru these different mediums what is the force that speeds it back up to C? Wouldn't Newtons laws prevent using light as a measuring tool?

@@benjaminharris6175 Very interesting.. i'm 55 and dropped out of school at 16 but the internet has given Me 20 years of education.. i say ur on to something.

You need to learn so many things. One if them is to be more humble and less ignorant.