Sun Definition and 1000 Threads

Hello. 1. Homework Statement I have to find formula for effective cross-section (σ) of catching a comet with the Sun. I know mass of the Sun (M), radious of the Sun (R) and initial velocity (v) of the comet (at a big distance from the Sun). Homework Equations σ=πb^2, where b is on the...

Hello. 1. Homework Statement I have to find formula for effective cross-section (σ) of catching a comet with the Sun. I know mass of the Sun (M), radious of the Sun (R) and initial velocity (v) of the comet (at a big distance from the Sun). Homework Equations σ=πb^2, where b is on the...

Is our Earth's sun is a dwarf star?

Hi everyone This thread is for showing your images of solar activity taken with YOUR cameras, telescopes etc. That is, don't post images from SDO, SOHO or any other professional sources unless you specifically want to ask "how do they do that and what are those solar features I can see? This...

How much would time pass between watching the sun set from ground level and then watching it set again from the top of a sky scraper? I heard once that this could be done using one of the towers of the World Trade Center. So I assume one could also do this using the Sears / Willis Tower in...

Sometimes it looks like there is a message here. Sun on 9/8/2017 - wavelengths 211, 193, 171 from http://sdowww.lmsal.com/suntoday/index.html?suntoday_date=2017-09-08 Beautiful!

Saving Earth - for a while: Could we shade the Earth from the Sun at a rate that keeps up with the Sun’s increase in Luminosity? There is a theoretical Dyson’s Ring that could be built around the Sun that would be used to tap the energy of the Sun. Could we construct something like that to...

I am picking this up as a continuation and extension of the idea laid out e.g. in @davenn 's thread "The Sun today - 9 July 2017 - nice spot group" https://www.physicsforums.com/threads/the-sun-today-9-july-2017-nice-spot-group.919696/ See also (for continuity purposes)...

I procrastinated big time about getting some solar filter or solar film or something to make my camera capable of filming the Sun, and now I can't find anything. I tried buying replacement glass for welding masks, but even with 4 sheets of it stacked together, the Sun blasts right through it...

1. The problem statement, all variables, and given/known data Venus is sometimes described as either the “Morning Star” or the “Evening Star”, since it can only be seen near sunrise and sunset, very close to the Sun in the sky. Why does Venus always appear close to the Sun in the sky for an...

How long does it take for the temperature on Earth to cool down after the sun has set? I want to know if the total solar eclipse will change the temperature.

Hi all, I'm trying to calculate the daily solar insolation (integrated solar irradiances from sunrise to sunset) for a given location and day of the year. For latitude 43.2° and April 15th, I get: H0 = (solar constant * scale factor for intra annual variation of sun-earth distance * 86400...

Hi all, According to the sunrise equation, the hour angle of the sun at sunset is: cos H = -tan(a)tan(d) where H = the hour angle, a = latitude and d = solar declination angle. This equation says that H at sunset = -H at sunrise. Now, I have a few questions concerning that: 1) I was...

AR2665 ... largest spot group for some time Canon 6D, 800mm, f11, 125th, ISO100 ( the 800mm is a 100-400mm L lens with a x2 teleconverter) With my eyesight going downhill, I have really been struggling of late to be able to get sharp manual focus Dave

If star start from a big ball of hidrogen and the all the neutron to make helium. Thx for help!

Sun produces neutrinos by sundry reactions: p+p→d+e++νe - called "pp" p+p+e→d+νe - called "pep" 3He+p→α+e++νe - called "hep" 3He+p+e→α+νe - never mentioned. What should it be called? "Heep"? Now, heep neutrinos should form a sharp line at a quite high energy. What is the intensity of heep line...

Homework Statement Consider the Earth's orbit around the sun orbit as circular. Suppose the sun slowly loses mass from mass M1 to mass M2. Suppose that the initial orbit is R1 and the final orbit is R2. Express R2 in terms of the other parameters. 2. The attempt at a solution The problem I'm...

by Ken Croswell New observations indicate that objects born with a mass just 6.7 per cent that of the Sun can shine for trillions of years rather than fizzle out as failed stars known as brown dwarfs. Link: New Scientist

Hi all, which sun has highest concentration of UVB, but least concentration of UVA (skin cancer culprit). Right now, I'm in equator area (Singapore) with only 2 seasons (just in case if geography has any effect local sun's UV ray distribution). I've heard a lot of people saying that morning sun...

I use several web sites to search the visible passes of the ISS over a given location. Then I calculate the Sun elevation as seen from the ISS and I get surprisingly low elevations; for example, I get ISS magnitude= -3.8 and Sun elevation at the ISS= -19.9 deg. I suppose that the atmospheric...

according to professor Einstein's theory space and time are one entity and can be defined as space-time. it states that that the faster we move in the space, slower the time passes for us. so if we are traveling of speed of light, we won't move in time at all. so how is that light from the sun...

so, I was told that only Up and Down are stable Quarks in the nucleus, and the others are only explained by observations in particular decay.

What is the Sun ray brightness quality after mirror reflection and what affects it? How to get the efficiency after reflection?

Bear with me, this is a very specific question for a scifi book I'm writing. If we had a ring in place of the moon, and you lived somewhere in the United States, how often would the ring intersect with the sun when it's setting (or rising, if it makes it easier). I know that it can take up to...

What is the reason for this? Is it because of the Earth's rotation?

A tree seed takes water and minerals(?) from the ground, carbon and oxygen(?) from the air, and heat and light(?) from the sun. When a tree dies and dries up, it can be used as firewood, a source of energy. Is there a way to capture that energy without the seed-tree scenario? i.e., but can we...

Eventually the Sun will go through its phases and cool down. Is it possible to calculate how long it will take for the surface to cool to 75 degrees Fahrenheit?

A big part of water on Earth come from comets at the very early ages of Earth so I suppose that the comets has same age as the Earth. The Earth and other objects come from a waste after creation of the Sun. The Sun come from cloud of hydrogen and helium mostly. It is star of 3rd-generation so I...

This has always been something that has interested me. 2 things that I have found from the internet is that 1.) The Sun viewed from Pluto is (150 or 250) times brighter than the full moon. It varies of course depending on where Pluto is in its orbit. 2.) The Sun is about 30 arcminutes viewed...

This question arose in the context of another thread. https://www.physicsforums.com/threads/q-re-article-constraints-on-dark-matter-in-the-solar-system.900573/#post-5669854 Wikipedia gives an estimated value for the DM density near the sun of 0.35 × GeV/cm3 = 6.2 ×10−25 g/cm3. The value of the...

Homework Statement My homework involves calculating the amount of energy the Earth receives from the Sun in a given year. I actually have the answer, but what I'm confused with is that the calculation says that the Sun "sees the cross section of the Earth, a circle". So in the calculation, we...

Hi folk, i need an help for this esercise. 1. Homework Statement Determines the rest mass lost by the sun every second for emission of radiation. It assumes that the surface temperature of the sun is 5700 K and the diameter ##D_s=1.4 × 10^9 m##. The Attempt at a Solution The solar nuclear...

I'm in the 11th hour of studying, and have run into a problem I can't seem to tackle from an old exam. I may be making some foolish mistakes, as I've now been staring at this thing for entirely too long. 1. Homework Statement (a) Calculate the force due to radiation pressure experienced by an...

If the sun suddenly disappeared, we wouldn't know it for about eight minutes because that's how long it would take the light to travel the distance between the sun and the earth. But I've often wondered; if the sun suddenly disappeared, would the Earth continue in its orbital path around the...

In the MinutePhysics video "How long is a day in the Sun?" it is said 24 hours on Earth is 86,400.0 seconds, but on the Sun 86,400.2 seconds would pass. However, if time passes slower with more massed objects, then wouldn't a twin on the Sun be younger than a twin on the Earth? If so, is the...

About a half-hour before sunset I saw part of a rainbow extending upwards from the horizon about 10 degrees. All seven colors from red to violet were visible from left to right, but they were somewhat faded out. What caused this partial rainbow which I saw about 30 degrees north of the setting...

Homework Statement At lunch, the Sun's thermal energy incident on the surface of the Earth is 1.4 kW/m^2. Given the radius of the Sun, R, distance from Earth, r, and treating the Sun like a perfect black body, calculate the total intensity of its radiation and determine its temperature...

Dear Forum, I am filmmaker from Berlin and despite physics focus back in high school I am really bad at it. I am trying to get my head around some ideas I am working on and would kindly ask you for some tiny calculations. I hope this is OK and maybe even fun for someone here? So my questions...

Of all the stars in our galaxy, how much of them belong to clusters?? Is our sun rare in terms of not belonging to any cluster? I can't find any sources on that

Homework Statement I know the moon does. I know it is because tidal forces fall off as 1/r3. But why? Mathematically, I mean. Homework Equations F = GMm/r2 The Attempt at a Solution None

Homework Statement Find the force exerted on a particle on the Earth by the sun. Homework Equations F = - GMm/r2 r = distance between sun and particle M = mass of sun G = Gravitational constant m = ? The Attempt at a Solution Should I be using the other mass as that of the earth, or that of...

Helly everyone. I'm new in physics and I don't understand many things there. What interests me the most is energy generation. I was mostly reading Wiki articles, and I found something I couldn't understand, so I'm asking for help. According to wiki, peak power output of the largest nuke ever was...

I was watching a show on one of the science channels a couple of nights ago and I think I heard that Jupiter's gravitational pull on the sun is around half a million miles (or could have been kilometers). Now, depending on Jupiter's position in relationship to Earths, at any time does it...

Hello there, I want to write a fortran program which gives me the right ascension and declination of the sun and the phase of the moon when a date and time is given. I just want to know how to write it and if there are any references that can help me. Thanks, Jadaav.

Hi! I guess this question must be easy, but it's driving me crazy: in what time of the year does the Earth "trails" the Sun in its current galactic movement towards Vega? And, could you please confirm that during this period Vega is not visible because it's always facing the "day side" of the...

Hello Forum There are three different mechanisms to transfer thermal energy: conduction, convection and radiation. It is well known that when two objects having different temperatures T1 and T2 are in contact, they will eventually reach a common intermediate temperature (the weighted average...

Hi all, I want to understand how retinal irradiance (Watts per square centimeters) from the sun is calculated. Some sources calculate 11W/cm^2 like this one...

I am trying to create a model/simulation for a pair of binary asteroids in orbit around the sun and I'm wondering what would the best way to do this? The restricted 3-body problem doesn't work as I can't assume any of the 3 bodies as having negligible effect right? However the full 3 body...

I'm trying to understand the physics of reflection to better draw objects. Normally, you see the reflection of a light source on metallic surfaces where the angle of incidence can equal the angle of reflection. This should reflect an image of the source that is approximately equal in size to how...

Wikipedia says that solar core has 15 millions of Kelvins ( https://en.wikipedia.org/wiki/Solar_core ), what translates into ~1.4 keV energy per degree of freedom. For nuclear fusion we need to take the two nuclei to distance of range of nuclear forces: ~1fm (...