The Sun is an almost perfectly symmetric yellow dwarf star [spectral class G2V] which is at the center of our Solar System.

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1answer
52 views

Refraction and scattered light for NLCs

For helping with judging NLC candidates (are they NLC or not) I have a set of formulas to calculate the minimum altitude (in km) of the candidate given an observed altitude (in degrees) of the ...
0
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1answer
258 views

If there was no Earth, what would be the acceleration of gravity from here from the Sun?

Suppose there were no Earth to pull us back and we're hanging in the solar system. Assuming no other force of gravity from other bodies, what would be the $g$ from the Sun?
4
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1answer
32 views

Are solar physics images of use to the night-time community?

I'm actually interested in cases of cross-discipline data re-use. I know that the SOHO/LASCO coronographs are used for comet finding, that solar telescopes were used to get information about Venus's ...
1
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1answer
663 views

What is the apparent diameter of the sun as seen from earth?

I know this may not be physically accurate. For my purposes, basically 3D renders, I am assuming the sun rays are parallel rays from an infinitely far lamp. If the sky is clear, what size would that ...
3
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1answer
2k views

How to determine day/night based on latitude, longitude and a date/time?

Is there a simple method of determining, given a UTC date/time, whether it is day or night at a given lat/long coordinate? I am currently using a formula based on a Sunrise/Sunset Algorithm from the ...
9
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2answers
3k views

Do photons lose energy while travelling through space? Or why are planets closer to the sun warmer?

My train of thought was the following: The Earth orbiting the Sun is at times 5 million kilometers closer to it than others, but this is almost irrelevant to the seasons. Instead, the temperature ...
13
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2answers
939 views

Is the length of the day increasing?

In Frontiers of Astronomy, Fred Hoyle advanced an idea from E.E.R.Holmberg that although the Earth's day was originally much shorter than it is now, and has lengthened owing to tidal friction, that ...
3
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0answers
35 views

Surface UV exposure with cooler star

If the sun's surface was ~ 4000K (and earth closer to compensate), the UV component of the radiation would be less. However, UV makes ozone via photolysis of oxygen. Also, the stratosphere would ...
2
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2answers
3k views

Are dangerous rays emitted during Solar Eclipse?

It is said one should avoid staring at Sun as it can damage the eyes, but it is also said that one should not come out in sun during eclipse as it emits dangerous rays. Is that true? If yes, why?
3
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1answer
97 views

Does the spectrum of Sol's emission change as it ages?

A follow-up to my earlier question How would one navigate interstellar space? that just occurred to me; albeit on a different tack. Sol is probably in a state of continuous flux. The change of state ...
2
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1answer
123 views

Get time from sun Azimuth

I want to know if I can determine the time where the sun's azimuth is at a given value. In other words, I want a function that takes the sun azimuth along with longitude or time zone and outputs the ...
8
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3answers
833 views

Are planetary orbits measured from the Sun's surface or centre?

I would imagine planetary orbits are measured from the Sun's centre and not its surface. Is that true? I can't find anywhere that actually states this.
5
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1answer
112 views

Is there an Algorithm to find the time when the sun is X degrees above the horizon for a given latitude B at date C

Is there an accurate algorithm / method to determine the precise time of day/night when the sun is X degrees above (or below) the horizon for a given latitude Y at date Z? Is this the same question ...
5
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3answers
2k views

Is a water world possible, and for how long could it be stable?

I have several questions regarding this topic. First, could a water world be stable for thousands of years with most of its surface remaining covered in water. What would it take for this to be ...
2
votes
1answer
4k views

Why don't we see solar and lunar eclipses often? [duplicate]

Since we see the new moon at least once in a month when the Moon gets in between of the Sun and the Moon at the night and as far as I know if this happens during the day, you'll get to see a solar ...
6
votes
1answer
56 views

Transit of Mercury: how did he see it?

On November 7, 1631 Pierre Gassendi saw the transit of Mercury across the face of the Sun. How did he see it? I mean what instrument was used to reduce the apparent brightness of the Sun?
5
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1answer
562 views

Reverse Sun position algorithm?

To find the sun's position (elevation, azimuth) we can use many algorithms including the PSA algorithm. These algorithm share the fact that the input is the local time, longitude and latitude and the ...
11
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1answer
547 views

What proportion of a star's hydrogen is consumed in its life?

I've heard in a lecture that a star like the sun would burn 3% of its Hydrogen before expiring. I would have thought it would be much more.
4
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1answer
389 views

Photons arriving from the Sun

Given that the Sun is a bit less than 10 light minutes away from Earth, is it correct to assume in principle (I understand actual processes in the core of the Sun make the situation at a photon's ...
6
votes
1answer
2k views

Why does the sun “shine brighter” some days?

Today, the sun seems extremely bright; more dazzling than usual, and even the roads seem to be brighter so it's not just when you look up in the sky. Is more light actually getting through (perhaps ...
10
votes
0answers
479 views

Why does the moon look bigger at the horizon? [duplicate]

Possible Duplicate: Why does the moon sometimes appear giant and a orange red color near the horizon? Why does the moon look bigger at horizon or skyline than at other times e.g. at ...
1
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1answer
3k views

What is the relationship between mass, speed and distance of a planet orbiting the sun?

After reading this fascinating story about a new exoplanet, I was wondering about how mass, speed and distance determine a circular orbit of a planet around a star. Given the mass of the sun and ...
-6
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1answer
155 views

Black out the sun?

How many observers would it take to cancel out the number of photons produced in a medium sized star like our Sun, thus making it dark? (I want to consume more photons than the star is generating)
4
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2answers
3k views

What is the luminosity per square meter hitting the Earth's surface from the Sun?

So I know that the Sun's luminosity is $3.839 \cdot 10^{26}$. What I want is the luminosity per square meter at the Earth's surface. So this is what I have got so far: I know the distance to the ...
12
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6answers
6k views

Is it safe to observe the sun through binoculars with welding glass in front? [closed]

I asked this on Reddit but didn't get much of a response. So here goes! I'm looking for low-cost ways to observe the Transit of Venus this summer. Since I'll only be able to see a few hours of it ...
5
votes
2answers
465 views

The “official” mass of the sun as unit?

I'm searching for the "official" mass of the sun as a unit in astrophysics. The mass of the sun can be calculated by: $M_{\odot}=\frac{4\pi^2\times(1 \ \text{ua})^3}{G\times(1\ \text{year})^2}$ So ...
4
votes
1answer
83 views

Is it proven that all “solar” neutrinos are coming from the Sun direction?

In "Observation of 8B solar neutrinos in the Kamiokande-II detector" (Phys.Rev.Lett., 63, 16(1989), http://prl.aps.org/pdf/PRL/v63/i1/p16_1) the Figure 2 shows that only small percentage of registered ...
6
votes
2answers
508 views

Is dark matter really present around the sun?

Recently I read an article that there is dark matter around the sun but if it is so, than why can we see it clearly. If it is called matter than it shall show some hindrance in radiation we receive ...
0
votes
1answer
285 views

Does a coronal mass ejection change solar neutrino emission rates?

Does the CME and neutrinos have any relation? CME is measured by Corona graphs.. How do they measure neutrinos coming from the sun? Does any of these have effects on earth's magnetic field or ...
0
votes
3answers
74 views

fit funtion to the Sun electron fluxes data

I'd like to fit a function to the Sun's electrons flux data (blue dots), please note that x,y axis are in the log scale. The green dots are the "best" fit from the gnuplot program. I have taken the ...
1
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1answer
181 views

Is there anything special about the Sun's photosphere in terms of density?

The Earth has a definite boundary between rocky/ watery surface and gaseous atmosphere. The same cannot be said of the sun. Even though the photosphere gives an apparent "edge" to the sun via the ...
9
votes
2answers
301 views

Effect of gravitation on light

Einstein predicted that the gravitational force can act on light. This was verified in one solar eclipse that light from a star near to the sun's disc bent due to Sun's gravity as predicted. Since ...
4
votes
1answer
192 views

Why isn't sunset time in sync with solstice?

The winter solstice in the Northern Hemisphere in 2011 is on December 22. But if I look at the sunset times for a location such as Washington, DC on the USNO site, the sunset time starts reversing ...
19
votes
1answer
288 views

The transit of Venus and solar neutrino rates

The following question was posed at the end of Maury Goodman's June 2012 long-baseline neutrino newsletter. During the Venus transit of the sun, were more solar neutrinos absorbed in Venus, or ...
11
votes
4answers
613 views

Is solar wind positively charged?

Many times I heared that the solar wind consists of protons and alpha particles. The both are positively charged, but are there electrons in solar wind?
0
votes
1answer
291 views

Does regular sky clouds stops the sun's ultraviolet rays?

I have an argue with an ex-Doctor of Medicine about the amount of ultraviolet light reaching us under the clear day sun and under the 100% cloudy sky. To what extent we can say that the sky clouds ...
0
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3answers
387 views

How does solar activity affect the ISS?

Currently the sun is launching some intense solar flares. http://www.guardian.co.uk/science/2011/feb/17/solar-flares-northern-lights-uk Th article I've linked also mentions how a "coronal mass ...
4
votes
1answer
1k views

Formula for getting time of sunrise at a particular location?

Is there a formula that can get sunrise at a particular latitude and longitude (and elevation from sea level)? If so, what it is? (Why does it work?)
4
votes
3answers
5k views

Solar Eclipse Viewing

I know it is not safe when viewing a solar eclipse to look directly at the sun. I know you can purchase solar eclipse glasses online but how do you make your own solar eclipse glasses that are safe to ...
0
votes
1answer
213 views

Exist some relationship between irradiance units and wavelenght of the incident sunlight?

Exist some relationship between irradiance units and wavelength of the incident sunlight? What about irradiance? I want to establish a relationship between wavelength and irradiance, because I would ...
3
votes
1answer
200 views

daylight length variation from year to year

I am doing some calculations to see how many hours of light does a specific location (identified by latitude and longitude) has in a specific day of the year. Contrary to my expectations I get a ...
1
vote
2answers
698 views

Could a solar flare cause the Earth's magnetic poles to reverse?

With all the hype of the impending "2012 Mayan doomsday" I was thinking it might be interesting to see what principles of physics prevent the theories of doomsday from occurring. One overarching ...
4
votes
2answers
689 views

What's the reason for the seasons?

In the diagram, it shows that the fundamental reason for different seasons is when the northern hemisphere is titled towards the sun there's summer in northern hemisphere and winter in southern ...
3
votes
1answer
3k views

What is actually meant by 'sun set' and 'sun rise' times, when taking into account the mirage due to light bending in the atmosphere

I’ve heard from the likes of Brian Cox that what we see of the sun during a sunset and sun rise is actually the mirage of the sun. The Sun has actually set/risen and we see it due to the way light is ...
1
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1answer
107 views

Neutrino beam energy

Neutrino is one of the most mysterious particles in todays physics. Even when values of some parameters like for example mass associated with it are not known (or there is great range of possible ...
3
votes
2answers
70 views

Can I determine whether it is night at a location by calculating only the sun's elevation?

There are many formulas for determining sunrise and sunset times for locations, but for my application I only need to know if it is day or night (given a time, latitude and longitude). After studying ...
3
votes
0answers
106 views

Was Aristarchos' method to compute Earth-Sun distance ever rediscovered in medieval or modern times?

Ancient Greek astronomer Aristarchos who lived around 300 BC found a method to compute the Eart-Sun distance by applying geometry. In this video about the cosmic distance ladder, at 26:30, Terence ...
3
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1answer
80 views

Can CMEs disturb a planet orbit?

Yesterday (March 6), a massive X-class solar flare erupted from the Sun. I was wondering if this kind of solar flares can affect in some way the orbit of a planet if aimed directly. Let's say, for ...
4
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1answer
71 views

What is the weekly average of coronal mass ejections the sun sends out?

What is the average number of coronal mass ejections that the sun sends out each week, including those that are not directed towards Earth?
4
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3answers
2k views

Does the sun cross over a given meridian line every day at the same time?

Let's say I have an imaginary meridian line over new york going from north to south. I know that the sun will not always be exactly on top of my head here in New York, but every day it will have to ...