Wikipedia:Reference desk/Archives/Science/2018 March 3

= March 3 =

CMB is remained from past age of universe or recent
I have three difficulties  in cosmology : 1.in the case so we really judge about the world, then what means just now in our universe ? 2. rotation mode of galaxy members, why we believe both orbital rotation of galaxy members and stability of galaxy shape and arms? 3. Either it is so that CMB is recent thermal Image of universe or it refers  very past time when world age was 380000 years?--Akbarmohammadzade (talk) 09:43, 3 March 2018 (UTC)
 * 1. We count time in cosmology using our reference frame as determined on earth. So that means that we are not moving at close to the speed of light compared to the rest of the universe. Barycentric Coordinate Time can be used, which cuts out gravitational time dilation of the Earth and Sun. In the past cosmology still described the known universe. So centuries ago, Earth and planets made up a much bigger component. If you see time as "Before Present", it means before 1 January 1950, so you could say that "now" is that date. To read more about "now" see Present, the stub Cosmic time or the more useful Chronology of the universe
 * 2.Our article mentioning spiral arm fails to say much at all. See also Scutum–Centaurus Arm and Perseus Arm and Orion Arm. But these do not mention how they were discovered or anything about long. term stability. The arms are probably due to density waves in the gas, resulting in star formation, with bright new big stars marking the arms. Graeme Bartlett (talk) 11:20, 3 March 2018 (UTC)
 * 3.Cosmic microwave background is believed to be ancient light. Graeme Bartlett (talk) 11:20, 3 March 2018 (UTC)

Eyelid anatomy
What is the name for the small flesh colored bump that can be seen on the the inside edge of the far corner of the eye (lateral commissure) when you pull the eye lid away from the eye horizontally? This http://slideplayer.com/8275868/25/images/3/%28a%29+Surface+anatomy+of+the+right+eye.jpg is the most detailed chart I could find but only shows the outer portion --User777123 (talk) 18:19, 3 March 2018 (UTC)


 * Do you mean the Canthus? Our article doesn't say much about it, but perhaps that's because there isn't much to say.   Dbfirs  21:42, 3 March 2018 (UTC)

It is near where the canthus is, but that is not it. It is a small bump seen on the inside edge of the lateral canthis.--User777123 (talk) 23:20, 3 March 2018 (UTC)

How laser printer drums work
In a laser printer (and similar printing devices), a laser 'writes' the image on a drum, that gets electrostatically charged on the spots to be printed. These get covered with toner that gets melted onto the paper.

The drum is covered with selenium or a polymer that can be electrostatically charged.

The question is why does the electrostatically charged spot hold its charge? Why doesn't the charge spread over the whole drum, defeating its purpose? Is that the normal behaviour of an electrostatic charge? What if you have lots of charges concentrated in a small spot and none around? Wouldn't these be pushed away? --Doroletho (talk) 22:26, 3 March 2018 (UTC)
 * Your description is not quite correct. The full surface of the drum is charged negatively. But it is covered by a semiconductor that is not (very) conductive under normal condition. The laser is adding energy to the parts of the drum not to be printed. The added energy allows electrons to move more freely (see photoconductivity), thus the negative charge can flow away from just the light-exposed spots, but remains on the others. --Stephan Schulz (talk) 22:56, 3 March 2018 (UTC)


 * In the dark state selenium will be an insulator, so electric charge will stay where it is. The light changes the selenium into a conductive state, so that those electrons escape from the surface. Graeme Bartlett (talk) 23:10, 3 March 2018 (UTC)