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52 votes
Accepted

How much of the surface of other planets is lit by the sun?

OK, let start with some assumptions: spherical objects and no atmospheric effects. Here's the relevant geometry with the object on the left representing a planet and the object on the right ...
GrapefruitIsAwesome's user avatar
48 votes
Accepted

How did the ancient cultures determine that the year was actually a fraction of an extra day beyond 365 days?

This is not so hard to do. All you really need is a bit of care, a few sticks and a convenient place to observe the sunrise or sunset. So note that there is a cycle of the year and you want to know ...
James K's user avatar
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46 votes

Can a lunar eclipse happen at night and be followed by a solar eclipse the next day?

No. A lunar eclipse occurs when the moon is on the opposite side of the Earth as the sun. A solar eclipse occurs when the moon is on the same side of the Earth as the sun. And it takes the moon 14 ...
James K's user avatar
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45 votes
Accepted

Why is there a year 1 B.C., a year 0, and a year 1 A.D. in NASA’s Five Millennium Canon of Solar Eclipses?

This is all explained on the home page All dates are astronomical dates. These match CE (or AD) dates for positive values but differ by 1 for BCE dates. The Gregorian calendar is used for all dates ...
James K's user avatar
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33 votes

How to describe the Sun's location to an alien from our Galaxy?

This has already been done. The pioneer 10 and 11 probes have a description of the solar system's location and Earth engraved for aliens to understand (or so one hopes). The physical parameters of our ...
planetmaker's user avatar
33 votes
Accepted

Is it theoretically possible for the Sun to go dark?

Is it theoretically possible for a statue to wave at you? After all the atoms in a statue are moving randomly, so they could (by chance) all move in the same direction. This doesn't happen. It is the ...
James K's user avatar
  • 126k
31 votes

Can a star be made of sun spots?

A sunspot is made of the same matter as the rest of the sun. The sun is a mixture of hydrogen and helium (and a trace of other elements) A sunspot is exactly the same mix. The only difference is that ...
James K's user avatar
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29 votes
Accepted

Why did the dust between the planets disappear during the birth of the solar system?

Dust happens in two ways. "Primordial dust" just condenses out of the protostellar material in the disc providing it gets cool enough and dense enough. "Second generation" dust is ...
ProfRob's user avatar
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28 votes
Accepted

The star that created our sun

There is no single progenitor of the Sun. The material that makes up the Solar System (or at least the elements heavier than helium) were made in approximately a billion stars that lived and died ...
ProfRob's user avatar
  • 156k
26 votes

Error in "Efficient Method for Calculating the time of Sunrise and Sunset" by Robin G Stuart

This is an error in the paper. The equation is based on $\nu - M = 2\varepsilon \sin M$ Where M is simplified to be $M = l + 1.3450$ and $\varepsilon = 0.0167$, the eccentricity of the Earth's orbit . ...
stanri's user avatar
  • 491
26 votes
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What caused pink flares during the eclipse

That would have been the so called 'solar prominences' i.e. eruptions of plasma on the surface of the Sun (see https://www.iflscience.com/next-months-total-solar-eclipse-could-come-with-bright-pink-...
Thomas's user avatar
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25 votes

How did the ancient cultures determine that the year was actually a fraction of an extra day beyond 365 days?

It's easier than you think to notice the fraction... simply because the rounding error compounds over the years! After a good amount of years, you notice that solstices are drifting from their ...
Offirmo's user avatar
  • 351
24 votes
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Earth is Tilted, but in reference to What Object / relative to what?

The orbit of the Earth around the Sun defines an orbital plane. The equator of the Earth is (currently) tilted at an angle of 23.4 degrees to this orbital plane. Or to put it another way, the spin-...
ProfRob's user avatar
  • 156k
23 votes
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Sun moves relative to the stellar background?

Everyone knows that you can't see stars during the day. Why is that? Prehistoric people might imagine that stars don't exist during the day. Children sometimes suppose that the stars are "turned ...
James K's user avatar
  • 126k
21 votes

What is the solar diameter?

This is a difficult measurement to make with accuracy. There are issues with the "fuzzy" edge of the sun, and the challenges of pointing a telescope at something so bright. If the ...
James K's user avatar
  • 126k
18 votes

How did the ancient cultures determine that the year was actually a fraction of an extra day beyond 365 days?

The ancient Egyptians appeared to know that the year was 365.25 days. This was established by observing on what day the heliacal rising of Sirius occurred (i.e. on what day that it first becomes ...
ProfRob's user avatar
  • 156k
18 votes
Accepted

Always orient a sundial towards polar north?

A sundial needs to be aligned with the planet's axis of rotation, with the gnomon pointed in towards the nearest pole, for it to work correctly. The point of the shadow will then give you your Local ...
Chappo Hasn't Forgotten's user avatar
17 votes

Why are the solar prominences visible during a total solar eclipse - orange? Is the sun orange?

There are several things going on here. Structures that are seen in emission off the photospheric limb of the Sun - know as prominences - are emitting a lot of light at the specific wavelength of the ...
ProfRob's user avatar
  • 156k
16 votes
Accepted

How to describe the Sun's location to an alien from our Galaxy?

If the travel was instantaneous (or say, less than a million years) it should be relatively easy to relocate the Sun from triangulation using well-known objects visible from anywhere in the Galaxy. If ...
ProfRob's user avatar
  • 156k
15 votes

Is it possible to view the sun and moon in the sky at the same time?

It is not only possible it is exceptionally common. When the moon is nearly new (and very close to the sun) it is not visible because the glare of the sun is too bright, and when the moon is nearly ...
James K's user avatar
  • 126k
14 votes

What can be learned from viewing the sun on earth during a total eclipse that cannot be studied by spacecraft in orbit?

It is true that many of the things that we used to use eclipses for can now be done from space, continuously. Eclipses are still important because they are usually much more easily accessible than ...
James K's user avatar
  • 126k
13 votes

Did the Sun's light always peak in the green wavelengths?

Nice question! Sun's spectral peak wavelength is currently 483 nm which falls under the category of green. Sun's wavelength changing In it's early days, the Sun was a lot cooler than it is today. So ...
Arjun's user avatar
  • 1,624
13 votes

At 45°N, how come the Sun rises in a northeasterly direction?

This is probably easiest to grasp by using some planetarium software (like Stellarium), and turn on the equatorial grid as in the images below (note the map distortion makes the "circles" ...
Greg Miller's user avatar
  • 5,932
12 votes

Did the Sun's light always peak in the green wavelengths?

No, but that's not why plants reflect green light The Sun, as well as the light of nearly all stars in the universe, had their peak wavelengths shift at some point during their life. In the case of ...
Alastor's user avatar
  • 2,668
12 votes

How would radiation pressure inside of the Sun affect an indestructible person?

Radiation force is totally negligible at the surface of the Sun - about one hundred thousandth the force due to gravity. The radiation force does grow as you move into the solar interior, but only as ...
ProfRob's user avatar
  • 156k
12 votes

Why when i divide the distance of sun to earth by golden ratio, the result starts with the last 5 digits of speed of light?

Coincidence Here're some reasons why: The speed of light is 299792458 m/s. It is also 1 s/s, 5.901e+10 feet/min, or 9457698889956.7 kilometers/year. The distance from the Sun to the Earth varies ...
Allure's user avatar
  • 4,719
12 votes
Accepted

Can a star be made of sun spots?

A sunspot is made out of the same stuff as the rest of the sun, it's just a relatively cool spot. Because it's cooler, it puts out less and redder light, but it's only dark in comparison to the rest ...
Darth Pseudonym's user avatar
11 votes

What is the meaning or information given by the solar image at 4500Å?

The 4500Å images (in the blue part of the visible light spectrum) are designed to show the Sun's visible "surface" or photosphere. I'm not 100% sure, but by the looks of it, the banding and ...
Matt Pitkin's user avatar
11 votes

Can a lunar eclipse happen at night and be followed by a solar eclipse the next day?

Yes… if you're on Mars. Earth's Moon is far enough from Earth that its synodic orbital period (i.e. the time between two full moons or two new moons) is about 29.5 Earth days. The time between a full ...
Ilmari Karonen's user avatar
11 votes

Will Earth become a gas giant when the Sun expands in 5 billion years?

The opposite. The Earth orbits at 30 km/s. The Sun's material would not have comparable net rotation, so the Earth would be subjected to a 30 km/s wind. This wind would easily strip off the Earth's ...
Sten's user avatar
  • 4,764

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