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Questions tagged [earth]

Questions regarding the planet on which humans live; the third planet from the Sun.

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Why does the Earth's axial tilt create an east-west variation in the analemma? [duplicate]

I've been reading about the Earth's analemma from Wikipedia, and I am having trouble visualizing one component. Let's build up to my question. If the Earth had a circular orbit and no axial tilt, the ...
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1answer
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Calculate eccentricity from apside altitudes? [closed]

I need to calculate the eccentricity of a satellite orbit with only the apside altitudes (height above the surface of the Earth), 400 and 1500 km. However, I don't know the semi-major axis ($a$) or ...
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5answers
12k views

How old is the oldest light visible from Earth?

Because light can only travel so fast, all of the light we see in the sky was emitted at a previous moment in time. So if for example we see a supernova or some other great stellar event, by the time ...
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2answers
136 views

When the asteroid hit the earth 65 mya did the earth's gravity pull change? By how much?

When the asteroid hit the earth 65 million years ago, did the earth's gravity pull change? By how much?
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1answer
252 views

What does the angle between plane of earth's orbit and ecliptic vary between?

What does the angle between the plane of the earth's orbit and the ecliptic (now about 23.5 degrees) vary between, and over what time scale?
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2answers
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How can Earth-Sun Lagrange points L1 & L2 even be semi stable considering the moon?

I know that the Earth-Sun Lagrange L1, L2, and L3 points are not considered stable over longer periods, especially when compared to L4 and L5... But, with the moon orbiting the Earth in the general ...
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2answers
52 views

Mass accumulation rate and orbit-time of earth

According to me following reason of mass accumulation of earth has been completely overlooked so far. The sunrays that fall on the oceans travel deep into water and finally get converted into mass ...
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1answer
404 views

Effect of the obliquity of the ecliptic / tilt of the Earth on the equation of time

In an attempting to answer the question “why aren’t changes in sunset and sunrise times symmetrical around the solstices ?” I’ve got stuck on being able to explain the effect of the obliquity of the ...
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329 views

Is the flat earth cosmology scientifically justifiable today? [closed]

With binoculars or telescopes you'd be able to see to other countries if the earth were flat. And looking out at the ocean we can see where the earth curves and things like the top of ships, not the ...
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1answer
2k views

What is the distance of the Earth's orbit around the Moon?

I realize the Earth and the Moon both orbit around their shared center of mass, and that in the case of the Earth and Moon this center is "inside" the Earth. However, I'm looking for an approach to ...
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3answers
225 views

How close would the sun have to get to Earth for there to be severe consequences?

According to earthsky.org the Earth gets 3 million miles closer to the Sun than its usual distance of about 93 million miles on average. My question is, how close would the earth have to be to the ...
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2answers
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Are there currently any planned or proposed missions to measure the gravitational fields of other planets in our solar system?

I just recently found out about the GRACE Nasa mission which basically mapped out the gravitational anomalies of earth as well as serving extensively in the study of earths geology and the movement of ...
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5answers
327 views

Why is sun's photosphere a million times less dense than air at the surface of the Earth?

Sun's photosphere is about 19 times as hot as Earth's surface. (Source: http://solar-center.stanford.edu/vitalstats.html) But Solar surface gravity is about 28 times terrestrial surface gravity. So,...
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1answer
246 views

What will the last day of humanity look like? [closed]

It's certain that human life on Earth will not go forever. Therefore there will be one last generation of humans on Earth. How will life look like for last few generations approaching the end? How ...
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1answer
70 views

Binary Orbit around the Earth?

Is a orbit possible where 2 objects going in opposite directions can intersect repeatedly with minor course corrections?
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52 views

Why is Earth a sphere? [duplicate]

Earth (and all of its 'neighbors') is a spheroid. Why is this? Earth could've been a cube, a tetrahedron (pyramid) or really any shape! But why a sphere?
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1answer
178 views

Temperature of Earth if tidal locked with the Sun?

Assume the Earth somehow stopped spinning once every ~24 hours, and instead started rotating at ~365 days per rotation, so it effectively would end up being tidal locked with the Sun. In this ...
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2answers
116 views

Do unattached objects contribute to a planet's gravity?

If you could measure Earth's gravity with infinite precision, and did so both with Earth and its full population, and Earth with no people, would there be a direct difference in gravity? Is this even ...
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1answer
189 views

Is Earth losing orbit? [duplicate]

Is the Earth losing or gaining distance from the sun overall? Could asteroids over time add weight to the Earth and push it farther from the sun more than having a degrading orbit around the sun? Does ...
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2answers
631 views

How to calculate the maximum and minimum solar azimuth at a given location?

Every Azimuth equation I have been able to locate so far depends on inputting a time, and I do not want to have to brute force the solution by simply trying all of the times. (See below for standard ...
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1answer
240 views

How large could a second moon of Earth be?

Question in the title. Let's say that I have a lot of garbage- mined-out asteroids, spent nuclear fuel, satellite debris, and just general trash. Also safe ways to get these into Earth orbit. Instead ...
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8answers
346 views

Explain to a 4-year old why people below the equator are not tilted or suspended upside down

So I just bought a globe for my extremely inquisitive soon to be 4-year old son. He knows the very basics of the solar system and knows that we live on planet Earth and also knows the concept of ...
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2answers
452 views

If the Earth is rotating counter clockwise, how does the sun rise from east?

I was very confused when I watched this video from 2:18 till 2:45. And it seems very clear that if the Earth is really rotating from west to east, shouldn't be the Sun rising from west and setting in ...
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1answer
411 views

Expression for length of sunrise/sunset as function of latitude and day-of-year

I would like to know how the length of sunrise/sunset (and also time between civil/nautical/astronomical twilight) varies with latitude and with day of year. Ideally what I am looking for is an ...
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3answers
350 views

Observed lunar distance data?

Where can I find free/open data for the observed (not calculated/theoretical) distance between the Earth & Moon? I want to see the observed distance of the Moon, hour by hour.
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2answers
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How long does it take the center of the Earth to complete a full orbit?

If we take midnight of 1/1/2017 in any country and mark in space where the center of the Earth is located, at what date, in the same country, has the center completed a full orbit. I am almost ...
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3answers
268 views

Moon looks too small in 3D model

I'm not sure if this is more a question for a 3D graphics forum, but I'm trying here first in case the answer has more to do with astronomy than 3D. I am creating a model of the Earth and Moon in a ...
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3answers
192 views

Is the shortest day duration constant?

Is the exact duration of the shortest day of a year (at the winter solstice in the northern hemisphere) always the same, for given latitude and longitude, or does it fluctuate? If it does, what is the ...
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1answer
64 views

Is it correct to assume that the relationship between an objects mass and size, is what decides if it’s a black hole or not?

I’m asking this question in reference to a scenario I saw posted a couple of days ago, where it’s stated that if you would shrink earth to the size of a cherry, it would become a black hole. Is it ...
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0answers
129 views

How does Ptolemy prove in the following excerpt that the Earth could not be outside of the axis spanning between the poles of the celestial sphere

I have trouble interpreting the following excerpt: “Against the first of these three positions militate the following arguments. If we imagined [the earth] removed towards the zenith or the nadir ...
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1answer
140 views

How did Ptolemy prove in the following excerpt that the Earth is not cylindrical?

I have trouble interpreting the following excerpt: “Nor could it [the Earth] be cylindrical, with the curved surface in the east-west direction, and the flat sides towards the poles of the ...
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1answer
98 views

Rotation of the Earth about its own axis [duplicate]

I am wondering how the Earth got its original angular velocity. What was the cause that made the Earth rotate about its own axis? What about its motion around the Sun? What gave the Earth the push to ...
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0answers
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If Earth had rings, how long would it take for the rings to loose orbit? [closed]

If Earth had rings, how long would it take for the rings to loose orbit? One of the answers in this question https://physics.stackexchange.com/questions/281828/if-earth-had-rings said we did at one ...
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1answer
159 views

At which winter hour is sun in zenith in DST?

When DST is introduced does it mean that the sun is in zenith one hour later (1pm winter local time) or one hour earlier (11am winter local time)? Edit: The location is New York.
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2answers
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Why isn't the day backwards between leap years?

So every four years, we add an extra day. A leap year. This is because a year is actually $365_{1/4}$ days long. But what happens between leap years? After two years, it would get dark at 8:00 AM ...
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1answer
254 views

How much could Earth's orbit shift without causing an ecological catastrophe?

Seeing the news about A/2017 U1 made me wonder what would happen if a similar object, but with a mass close to Earth's, had a close call with Earth. Could it shift Earth's orbit enough to quickly and ...
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131 views

spin–orbit resonance, between moon and the earth

if this happens in the future what will be the consecuences of this?. Consecuences for the life or the climate conditions.
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101 views

At each stage and during each transition of the Sun, is there a region the Earth could theoretically orbit and support life? [closed]

As I understand it, the Sun will transition from its current phase as a 'yellow dwarf', to a red giant, and finally to a white dwarf. Even during these phases I understand there are transitional ...
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2answers
748 views

Can we actually predict an asteroid impact? [duplicate]

I have been seeing all these "hoaxes" on the internet about Planet X and how it would destroy Earth, on September 23rd 2017. It didn't happen. I started to wonder if it's possible - with our current ...
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1answer
376 views

How to calculate true equinox position?

I'm trying to calculate the state of the Earth at a given time using Keplerian orbital elements from this page. It has the following instruction: Compute the coordinates, $\mathbf r_{ecl}$, in ...
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3answers
493 views

Why is right ascension measured on a 24 hour scale rather than a 23 hours and 56 minutes scale?

From several texts I have read, I have learned that right ascension is measured on a scale of 24 hours. I understand that Earth rotates almost exactly 360 degrees relative to distant objects, which is ...
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1answer
98 views

What contributes the most to the seasonal temperature variation?

The seasonal temperature is ultimately due to the precession of the Earth around the axis. But what I'm curious about is... is it due more to the side experiencing winter being farther from the sun ...
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2answers
93 views

Can we, with arbitrary precision, calculate what's the place on earth that's closest to the sun on a given day?

Can we, with arbitrary precision, calculate what's the place on earth that's closest to the sun on a given date? If so, what's the math like? Say, if I wanted to calculate this within 1m, 10cm or 1cm ...
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2answers
164 views

What kind of a visual trajectory would an asteroid have if it were to hit Earth?

Let's say that Peter has a set of superb telescopes and he's watching the sky every night, for 3-4 months. He may not know it just yet, but there is an asteroid heading towards Earth, on a crash ...
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1answer
3k views

If an asteroid was to collide with Earth, how much warning would we have?

I was talking to my 9-year-old son about the Florence asteroid that is passing close to the earth. He wanted to view youtube videos about that asteroids, and we saw the starting of this one https://...
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1answer
199 views

Why do we we even exist? [closed]

It came to my mind one day that why does this universe even exist and why do we even exist and like we are enclosed in the so called atmosphere and a floating rock in space called the Earth, so is ...
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2answers
494 views

On the Equator, why are the shortest shadows seen at 11:32, and not at Noon?

On Equator, why do objects cast the shortest shadows at 11:32 and not 12:00? For instance, this happens in Costa Rica.
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1answer
76 views

GEO and HEO images of Earth

I would like to see some GEO and HEO images of Earth. But I can't find a good source. There are a lot of LEO images of Earth but I can'f find any raw images from higher (preferably 30,000km+) ...
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1answer
136 views

Why would there be no day/night cycle even though the firmament would still be rotating, according to Copernicus

In chapter 6 of "The Revolutions of the Heavenly Spheres" where Copernicus maintains that the heavens are immense compared to the size of the Earth, the Edward Rosen translation of the book states ...
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1answer
105 views

How did we first determine the Earth's departure from sphericity?

I'm quite interested to know the history of the study of the Earth's departure from spherical symmetry. What were the first methods used to model the non-spherical geometry of the Earth? For example, ...