# Tag Info

## Hot answers tagged the-sun

8

Local Mean time is based on the Average position of the sun. The actual sun might not be on the meridian at noon LMT but on average. Some times the sun moves faster and sometimes slower (for example due to the elliptical orbit of the Earth). But if you replace the sun with an orb that moves constantly and has the same average motion as the sun. This orb will ...

7

It depends on which region you consider. The lower corona has a plasma number density of the order of $10^9 cm^{-3}$, the upper corona about $10^5 cm^{-3}$. This is all quite variable though, depending for instance on the solar activity. Theoretically, the corona is still quite poorly understood, so its physical parameters can generally only be estimated ...

6

It's geomety: The day has 24 hours. The circle has 360°. So the sky "moves" 15° per hour due to the Earth's rotation of 360° in 24 hours once around its axis. Assuming that an object is approximately fixed at an infinitely distant place within this time span (not true for solar system objects, but as rule of thumb it's ok), an object on the ...

4

Time zones have a reference meridian where the average noon is at 12h local time (disregarding daylight saving). The location of the 0° meridian is essentially totally arbitrary and goes through Greenwich observatory just by definition and convention and general agreement between the countries to faciliate a common understanding of time. Before that ...

3

To supplement Rory Alsop's answer, it is also possible to detect some CMEs through X-ray observations of the Sun. We have a few satellites continually monitoring the Sun, and if we're lucky we'll see the CME when it erupts. That gives an early warning on the order of a day. "Lucky" because it is coming right at us, so sometimes it's not obvious. ...

2

Could be as much as an hour. Looking at NASA's Space Weather Prediction Centre page on CMEs Imminent CME arrival is first observed by the Deep Space Climate Observatory (DSCOVR) satellite, located at the L1 orbital area. Sudden increases in density, total interplanetary magnetic field (IMF) strength, and solar wind speed at the DSCOVR spacecraft indicate ...

2

My guess is the reflector is shaped in a parabolic curve. The reason is that if you look at the inversed problem for sunlight concentrators as shown in the figure here, the sunlight will be focused to a point. Now, let's image the sunlight is shining from the other side of the reflector in the same figure, then the reflected light will be lines extended ...

2

The inner planets like Earth formed initially from the coalescence of solids in the protoplanetary disc. The disc itself would have a similar overall composition to the Sun itself, but close to the protosun, the composition of the solids would be quite different. The high condensation temperatures of solids containing iron, silicon and oxygen mean that they ...

1

Like 14 April 2022 is when solar noon is at 12pm clock time. So can the measurement starts from that point? The modern definition of the Equation of Time (EOT), according to the Astronomical Almanac of the USNO, is that it's the difference apparent solar time minus mean solar time. The EOT has two principle causes: the eccentricity of the Earth's orbit, and ...

1

Partial answer so far This is a really interesting question! I've just started looking at Inferring the interplanetary dust properties from remote observations and simulations and surprisingly the power law fit to observed solar system dust temperature between 0.5 and 1.5 AU as shown in Eq. 2 varies as $d^{-1/3}$ instead of $d^{-1/2}$ in your equation. It ...

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