APOD: Aphelion Sunrise (2017 Jul 05)

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APOD: Aphelion Sunrise (2017 Jul 05)

Postby APOD Robot » Wed Jul 05, 2017 4:07 am

Image Aphelion Sunrise

Explanation: On July 3rd, planet Earth reached aphelion, the farthest point in its elliptical orbit around the Sun. Each year, this day of the most distant Sun happens to occur during winter in the southern hemisphere. That's where this aphelion sunrise from 2015 was captured in a time series composite against the skyline of Brisbane, Australia. Of course, seasons for our fair planet are not determined by distance to the Sun, but by the tilt of Earth's rotational axis with respect to the ecliptic, the plane of its orbit. Fondly known as the obliquity of the ecliptic, the angle of the tilt is about 23.4 degrees from perpendicular to the orbital plane. So the most distant sunrise occurs during northern summer, when the planet's north pole is tilted toward the Sun and the north enjoys longer, warmer days.

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Re: APOD: Aphelion Sunrise (2017 Jul 05)

Postby ta152h0 » Wed Jul 05, 2017 5:58 am

here at 48 deg North, the further away the sun is, the hotter it gets , at 122 deg West
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Re: APOD: Aphelion Sunrise (2017 Jul 05)

Postby Boomer12k » Wed Jul 05, 2017 6:33 am

Very nice, had not heard of this... got to get out more.
Had a bad night with my scope. Seems to have lost its programming, the handset is lit, but blank, and nothing comes on.... I am thinking... "Dark Matter Squirrels from Beyond the 5th Dimension"... What else could it possibly be????

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Re: APOD: Aphelion Sunrise (2017 Jul 05)

Postby Ann » Wed Jul 05, 2017 8:17 am

ta152h0 wrote:here at 48 deg North, the further away the sun is, the hotter it gets , at 122 deg West


The fact that the Earth is farthest from the Sun in July, when the northern hemisphere is tipped towards the Sun, and closest in January when the northern hemisphere is tipped away from the Sun, may protect us northerners from some unpleasant weather records.

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Re: APOD: Aphelion Sunrise (2017 Jul 05)

Postby De58te » Wed Jul 05, 2017 8:44 am

I am not sure about the unpleasant records. If the position of the sun is based on the elliptical orbit, then the precession of the equinoxes means that some 13,000 years ago the Sun was farthest away in the Northern Hemisphere in the winter. 13,000 years ago was when the last Ice Age began melting up and warming. 26,000 years ago when the situation was the same as today, the Northern Hemisphere was in the midst of the Ice Age. 39,000 years ago when the Sun was the farthest away again in the North, is when the Ice Age began. My guess is that the Sun isn't the main cause of climate change, but itcould also be influenced by volcanoes, continental drift, ocean currents, and yes, man made climate change.

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Re: APOD: Aphelion Sunrise (2017 Jul 05)

Postby Guest » Wed Jul 05, 2017 8:45 am

Ann wrote: may protect us northerners from some unpleasant weather records.
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That and the failing gulf stream, Ann!

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Re: APOD: Aphelion Sunrise (2017 Jul 05)

Postby neufer » Wed Jul 05, 2017 11:45 am

De58te wrote:
I am not sure about the unpleasant records. If the position of the sun is based on the elliptical orbit, then the precession of the equinoxes means that some 13,000 years ago the Sun was farthest away in the Northern Hemisphere in the winter. 13,000 years ago was when the last Ice Age began melting up and warming. 26,000 years ago when the situation was the same as today, the Northern Hemisphere was in the midst of the Ice Age. 39,000 years ago when the Sun was the farthest away again in the North, is when the Ice Age began. My guess is that the Sun isn't the main cause of climate change, but it could also be influenced by volcanoes, continental drift, ocean currents, and yes, man made climate change.
https://en.wikipedia.org/wiki/Milankovitch_cycles wrote:
<<Milankovitch cycles describe the collective effects of changes in the Earth's movements on its climate over thousands of years. The term is named after Serbian geophysicist and astronomer Milutin Milanković. In the 1920s, he theorized that variations in eccentricity, axial tilt, and precession of the Earth's orbit resulted in cyclical variation in the solar radiation reaching the Earth, and that this orbital forcing strongly influenced climatic patterns on Earth.

The angle of the Earth's axial tilt with respect to the orbital plane (the obliquity of the ecliptic) varies between 22.1° and 24.5°, over a cycle of about 41,000 years. The current tilt is 23.44°, roughly halfway between its extreme values. The tilt last reached its maximum in 8,700 BCE. It is now in the decreasing phase of its cycle, and will reach its minimum around the year 11,800 CE. Increased tilt increases the total annual solar radiation at higher latitudes, and decreases the total closer to the equator. The current trend of decreasing tilt, by itself, will promote milder seasons (warmer winters and colder summers), as well as an overall cooling trend. Because most of the planet's snow and ice lies at high latitude, decreasing tilt may encourage the onset of an ice age for two reasons: There is less overall summer insolation, and also less insolation at higher latitudes, which melts less of the previous winter's snow and ice.

The Earth's orbit approximates an ellipse. Eccentricity measures the departure of this ellipse from circularity. The shape of the Earth's orbit varies between nearly circular (with the lowest eccentricity of 0.000055) and mildly elliptical (highest eccentricity of 0.0679) Its geometric or logarithmic mean is 0.0019. The major component of these variations occurs with a period of 413,000 years (eccentricity variation of ±0.012). Other components have 95,000-year and 125,000-year cycles. They loosely combine into a 100,000-year cycle (variation of −0.03 to +0.02). The present eccentricity is 0.017 and decreasing..

Of all the orbital cycles, Milankovitch believed that obliquity had the greatest effect on climate, and that it did so by varying the summer insolation in northern high latitudes. Therefore, he deduced a 41,000-year period for ice ages. However, subsequent research has shown that ice age cycles of the Quaternary glaciation over the last million years have been at a 100,000-year period, which matches the eccentricity cycle.

Various explanations for this discrepancy have been proposed, including frequency modulation or various feedbacks (from carbon dioxide, cosmic rays, or from ice sheet dynamics). Some models can reproduce the 100,000-year cycles as a result of non-linear interactions between small changes in the Earth's orbit and internal oscillations of the climate system.

Jung-Eun Lee of Brown University proposes that precession changes the amount of energy that Earth absorbs, because the southern hemisphere's greater ability to grow sea ice reflects more energy away from Earth. Moreover, Lee says, "Precession only matters when eccentricity is large. That's why we see a stronger 100,000-year pace than a 21,000-year pace."

Some have argued that the length of the climate record is insufficient to establish a statistically significant relationship between climate and eccentricity variations.>>
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