# Tag Info

148

This is an interesting question, but it lacks a key factor that is crucial to the answer: TIME. The point on Earth closest to the Sun varies through time, so the question can be asked about any moment in time, or over periods of time. Let's analyze the factors involved. At any given moment in time, the point on Earth's surface that is closest to the Sun is ...

54

The curve where latitude and longitude are equal is not a great circle. But as joe khool writes in his excellent answer, it's called the curve of Viviani! It's easy to see that the curve is not a great circle, because, using naïve spherical coordinates (in radians) $(\phi,\lambda)$ with $\lambda$ being longitude and $\phi$ being latitude (zero at equator), ...

22

Normally in the absence of rotation, the natural tenancy of gravity is to pull the Earth together in the shape of a sphere. However the Earth in fact bulges at the equator, and the diameter across the equatorial plane is 42.72 km more than the diameter from pole to pole. This is due to the rotation of the Earth. As we can see in the image above, the ...

20

If the Earth was a sphere, then the curve in the last picture of tfb's answer is the curve of Viviani; otherwise, if you make the oblate spheroid assumption, you get a slightly distorted version of this curve. More generally, a clélie is the name given to any spherical curve where the longitude $\varphi$ and colatitude $\theta$ have the relationship \$\...

15

Actually, the reason why the Earth is not a sphere is twofold: the Earth is rotating and has been rotating for a long time the Earth is not perfectly rigid, it can even be considered as a viscous fluid on long timescales If the Earth were not rotating, it would be a sphere. If the Earth had started to rotate very recently, it wouldn't be at equilibrium, ...

10

It is impossible to know. Solar flares can have more than 500,000 kilometers. So if we consider them part of the sun, the moment when the earth is closer to the sun can be very different from perihelion if a big flare happens, making much of what was discussed in other answers irrelevant.

10

One way to approach this is to treat the Earth as an oblate ellipsoid. This would mean the errors arise from the uncertainties in the Earth's equatorial radius and the flattening. From Groten, "Fundamental Parameters and Current (2004) Best Estimates of the Parameters of Common Relevance to Astronomy, Geodesy, and Geodynamics," Journal of Geodesy 77:10-11, ...

7

Talking about the volume of the Earth, we have to ignore that it is not static but in fact highly dynamic. The tides alone make the height differ by up to 50 cm. The information I take is from a 2003 article from esri by Witold Fraczek. As you said, we have different understandings of the Earth. Approximations are made to make calculations easier (and ...

7

That the Earth is approximately an oblate spheroid is best explained by energy. Place a marble in a bowl. No matter where you place it, it will eventually come to rest at the bottom of the bowl. This is the position that minimizes the total energy of the marble subject to the constraint of being in the bowl. Suspend a chain between two posts. When the chain ...

6

These are visco-elastic oscillations that cause virtually no permanent deformation. Following the Tohoku 2011 earthquake, this gravimeter in Metsähovi, Finland, measured a radial oscillation mode amplitude of 0.06 mm. The Earth's radius is 6371 km. So the resulting strains would be extremely small. All but the lowest radial mode decays after a few days ...

6

The centre of the Earth is the only true unchanging datum. Land masses rise and fall due to geological actions such as melting of land based ice sheets, volcanism, plate tectonics, erosion, sedimentation and ground stresses causing land masses to move relative to one another at faults. As stated here, sea level changes resulting from, Eustatic change (...

6

In short, the current volume of the earth is known to great precision and modern measurements show no significant expansion at meaningful scales. Facing 20th century evidence that points on the globe -- such as the edges of continents -- that are now distant from each other were once adjacent, some scientists argued that the only explanation was the ongoing ...

5

In short, weird things happen when you combine things that don't combine in nature: the Earth as a perfect sphere the Earth spinning on an axis Einstein's equivalence principle tells us that accelerations are all the same, no matter what's causing them. So you just add the acceleration vectors up. The (real) Earth has an equatorial bulge because a stable ...

4

The point on the surface of the Earth where the Sun is currently immediately overhead is called the Zenith Point. Its Latitude and Longitude correspond to the Declination and Greenwich Hour Angle of the Sun. These data points can be approximated to any degree of accuracy and timeframe by a Fourier series of n terms. Accuracy sufficient for sextant work ...

3

If the Earth were a perfect ball, which it is not, and had a perfectly smooth and even surface with no basins or irregularities, water would tend to move toward the equator, where it would form a bulge. Meanwhile, gravity would be pulling on this bulge and trying to drag it down, thus preventing it getting any higher and stopping the flow of water into it. ...

3

The UTM coordinate system, is a kind of Transverse Mercator projection separated in longitude bands and restricted in latitud extent such that the distortions associated with the projection remain small. Also, the UTM coordinate system is conformal projection. Therefore, it preserves the angles. That means that within the UTM zones, a straight line in UTM ...

3

Instead of the Nagy prism formula, I suggest you to use the formula quoted in the following paper: B. Banerjee, S.P. Das Gupta (1977): "Gravitational attraction of a rectangular parallelepiped" Geophysics, vol. 42, n. 5, pp. 1053-1055 doi: 10.1190/1.1440766 I wrote, in Fortran, a TC program based on that formula. If you read the paper you better ...

2

I have recently had to deal with the same problem and tackled it in Matlab, If it helps, here's a link to it on the file exchange https://au.mathworks.com/matlabcentral/fileexchange/57349-nagyprism-x1-x2-y1-y2-h-rho- Here is the code: % A function to perform terrain corrections using the Nagy % prism formula. % To calculate the terrain correction for a ...

2

I did a little poking around and came across a few projects that might be interesting. Based on the work of Peter Bird (2003) there's a github project (fraxen/tectonicplates) that hosts georeferenced data of most major plate boundaries. Seeing as you're interested more in minor plate dynamics, there's another project called GPlates that is an multi-OS open ...

2

There are some wonderful answers here, but I think a simplified plain English answer would be helpful. Barring any nearby mountains, and various foibles, the closest point to the sun at the June solstice is where it is midday on the tropic of Cancer. At the December solstice, it is where it is midday on the tropic of Capricorn. At equinox it is where it is ...

2

Whichever spot on the surface of the Earth is experiencing Lahaina Noon, or would be if it wasn't cloudy, is at the subsolar point and pointed directly at the Sun, moreso than any other point on Earth at that moment. Of course, you could get closer to the sun by climbing higher. If you were able to be at the summit of Chimborazo volcano in Ecuador (point ...

1

It is extremely unlikely to be a sink hole. They are characteristic of waterlogged limestone country such as is found in Florida. Hollows are sometimes found in flows of igneous rock where there has been volcanic activity. Some hollows are large gas bubbles which were trapped when the rock around them solidified, but probably the most common hollows in ...

1

At any one specific moment the subsolar point is the point on Earth that is closest to the Sun at that specific moment. The subsolar point on a planet is the point at which its sun is perceived to be directly overhead (at the zenith); that is, where the sun's rays strike the planet exactly perpendicular to its surface. It can also mean the point closest ...

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