Questions tagged [earth]

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

Filter by
Sorted by
Tagged with
11
votes
1answer
3k 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 ...
3
votes
3answers
4k 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 ...
2
votes
2answers
71 views

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 ...
3
votes
5answers
680 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,...
1
vote
1answer
334 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 ...
1
vote
1answer
74 views

Binary Orbit around the Earth?

Is a orbit possible where 2 objects going in opposite directions can intersect repeatedly with minor course corrections?
2
votes
0answers
58 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?
8
votes
1answer
394 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 ...
4
votes
2answers
124 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 ...
2
votes
1answer
290 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 ...
3
votes
2answers
2k 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 ...
4
votes
1answer
284 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 ...
14
votes
8answers
740 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 ...
3
votes
2answers
2k 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 ...
3
votes
1answer
890 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 ...
4
votes
3answers
837 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.
1
vote
2answers
337 views

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 ...
4
votes
3answers
392 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 ...
2
votes
3answers
340 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 ...
2
votes
1answer
70 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 ...
2
votes
0answers
184 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 ...
3
votes
1answer
235 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 ...
1
vote
1answer
355 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 ...
1
vote
0answers
219 views

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 ...
-1
votes
1answer
356 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.
5
votes
2answers
340 views

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 ...
1
vote
1answer
298 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 ...
-3
votes
1answer
188 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.
1
vote
0answers
115 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 ...
1
vote
2answers
1k 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 ...
0
votes
1answer
914 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 ...
4
votes
3answers
1k 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 ...
1
vote
1answer
206 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 ...
0
votes
2answers
106 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 ...
4
votes
2answers
205 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 ...
5
votes
1answer
7k 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://...
0
votes
1answer
279 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 ...
0
votes
2answers
1k 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.
2
votes
1answer
103 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+) ...
0
votes
1answer
175 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 ...
10
votes
2answers
226 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, ...
2
votes
1answer
750 views

How long was an early Earth year? [duplicate]

Roughly how long did it use to take for the early Earth 4.5~ billion years ago to complete one revolution around the Sun? (I know the Earth was spinning much faster, so a day would only take 2-3 ...
1
vote
2answers
477 views

If a comet strikes a glacier, does it make a print on the land below?

The Younger Dryas Impact Theory describes an asteroid impact in Northern America, possibly the eastern part of Hudson Bay, which contributed to the end of the last ice age. If a comet strikes a ...
2
votes
1answer
260 views

How have we measured the radius of the Earth (old and new)?

I'd imagine ancient methods are fun exercises in geometry. how has the measurement has evolved over time? The first method is credited to Eratosthenes. He knew that during the summer solstice in ...
1
vote
1answer
135 views

How are the elevations of the poles proportionate to distances of earth that have been traversed according to Copernicus

In chapter 2 of "The Revolutions of the Heavenly Spheres" where Copernicus maintains that the Earth is spherical, the Edward Rosen translation of the book states that the elevations of the poles ...
2
votes
2answers
480 views

Which would be safer: removing hydrogen or adding hydrogen to our sun?

If we want to extend the lifespan of our habitable zone safely, would it be safer to institute a yearly 'tax' on our suns outer layer of hydrogen, or a yearly 'subsidy' to our suns outer layer of ...
8
votes
1answer
2k views

How can I calculate the time between sunset and actual darkness?

I would like to know the time it takes to go from sunset to dark based on GPS location. In addition, ideally I would also like to have a formula that determines the percentage of sunlight at each ...
1
vote
2answers
2k views

Size and Mass of a typical “small” asteroid that impacts the Earth?

I'm looking for some realistic data about the size (in meters) and mass (in kg) of a typical small asteroids that impact the Earth, without disintegrating in the atmosphere. Any suggestion ?
3
votes
2answers
935 views

Umbra, penumbra and antumbra

I'm trying to understand following schema of the wikipedia page here. Image subtitle is "Umbra, penumbra, and antumbra, for a lunar eclipse". Distances and sizes are not to scale. If distance ...
3
votes
3answers
217 views

Problem about orbiting of a satelite

Problem: There is an satellite that orbits the Earth. Its orbit is circular and its orbital plane is perpendicular to Earth's Equatorial Plane. It orbits is such that a person who is on equator see ...

1
3 4
5
6 7
10