Summer/Winter and Precession.

[interstellaryeller]

Right now Polaris is our north polar star. In 12,000 years Alpha lyrae will be, correct? How will this effect the summer in the northern hemisphere. Will are days be even longer than they are now and the Suns cross the meridan higher in the sky? A interesting speculation. And will contellations like Sagittarius ride higher in our night sky?

[Chris Peterson]

Right now Polaris is our north polar star. In 12,000 years Alpha lyrae will be, correct? How will this effect the summer in the northern hemisphere. Will are days be even longer than they are now and the Suns cross the meridan higher in the sky? A interesting speculation. And will contellations like Sagittarius ride higher in our night sky?

The Earth's obliquity (axial tilt) doesn't change much*, so as the orientation changes due to precession, there is little effect on climate. The Sun's path across the sky (relative to the horizon) won't change because of precession. One thing that may have some effect, however, is the relationship between the orientation of the axis and Earth's position in its elliptical orbit. Right now, perihelion occurs in January, and aphelion occurs in July. So the Earth is receiving more radiation during the northern winter, and less during the southern winter. This probably has some effect on the northern and southern climates, although picking it out from larger effects, such as the different ways oceans moderate climate in the two hemispheres, is difficult. As the pole precesses, however, the relationship between between the seasons and the orbital position will shift.

The positions of the constellations will certainly shift, and in the case of Sagittarius, it will reach a higher declination than it does now.

*The obliquity isn't absolutely fixed, but varies about a degree on either side of the current value of 23.4°, over a period of about 42,000 years, which isn't related to the 25,800 year period of axial precession.

[neufer]

Right now Polaris is our north polar star. In 12,000 years Alpha lyrae will be, correct? How will this effect the summer in the northern hemisphere.

In about 10,000 years the boreal summer solstice sun will be near perihelion [and the North Polar star will be Delta Cygni (Ruc)]. This will indeed make summers in the northern hemisphere hotter but not nearly so hot as they were just 10,000 years ago when the boreal summer solstice sun was also at perihelion [and the North Polar star was Delta Cygni (Ruc) Tau Herculis]. This is because both the obliquity and the eccentricity of the earth's orbit have been on the decline for the last 10,000 years and they should continue to decline over the next 10,000 years.
http://en.wikipedia.org/wiki/Precession_(astronomy)
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Memorable quotes for 10,000 BC (2008):
D'Leh: [to Tic'Tic] We need you.

Tick tock ... tick: Extra second added to 2008
By Jim Wolf Reuters
Monday, December 29, 2008; 10:00 AM

WASHINGTON (Reuters) - Those eager to put 2008 behind them will have to hold their good-byes for just a moment this New Year's Eve.

The world's official timekeepers have added a "leap second" to the last day of the year on Wednesday, to help match clocks to the Earth's slowing spin on its axis, which takes place at ever-changing rates affected by tides and other factors.

The U.S. Naval Observatory, keeper of the Pentagon's master clock, said it would add the extra second on Wednesday in coordination with the world's atomic clocks at 23 hours, 59 minutes and 59 seconds Coordinated Universal Time, or UTC. That corresponds to 6:59:59 p.m. EST (23:59:59 GMT), when an extra second will tick by -- the 24th to be added to UTC since 1972, when the practice began.

UTC is the time scale kept by highly precise atomic clocks around the world, accurate to about a billionth of a second per day, the Naval Observatory says. For those with a need for precision timing, it has replaced Greenwich Mean Time, or GMT.

The decision to add or remove a second is the responsibility of the International Earth Rotation and Reference Systems Service, based on its monitoring of the Earth's rotation. The goal is to make sure clocks vary from the Earth's rotational time by no more than 0.9 seconds before an adjustment. That keeps UTC in sync with the position of the sun above the Earth. Mechanisms such as the Internet-based Network Time Protocol and the satellite-based Global Positioning System depend on precision timing.

The first leap second was introduced into UTC on June 30, 1972. The last was added on December 31, 2005. They have been added at intervals ranging from six months to seven years, Daniel Gambis, head of the IERS Earth Orientation Center at the Observatoire de Paris, wrote in an explanatory piece this month (http://hpiers.obspm.fr/eop-pc/).

Among the reasons for Earth's slowing whirl on its axis are the braking action of tides, snow or the lack of it at the polar ice caps, solar wind, space dust and magnetic storms, according to the U.S. Commerce Department's National Institute of Standards and Technology, another timekeeper.

By contrast, a leap day, February 29, occurs once every four years because a complete turn around the sun -- our year with all its seasons -- takes about 365 days and six hours.

In 1970, an international agreement established two time scales: one based on the Earth's rotation and another on highly accurate atomic clocks.

The U.S. Naval Observatory's master clock is based on a system that now includes 50 atomic clocks, 36 based on the element cesium and 14 known as hydrogen masers.

With the Earth's rotation gradually slowing, the periodic insertion of a leap second into the atomic time scale is needed to keep the two systems within a second of each other.

Our earth based time system is quite well defined and it makes perfect sense to say that SN1054 took place at a point in space time D light years away and D+954 years in the past. The real problem lies in the fact that D [~ 6300] is a little hard to define precisely with current technology.

Likewise, the boundaries of many western U.S. states were defined according to the American Meridian [through the U.S. Naval Observatory] NOT the Greenwich Meridian primarily because land surveying was the only accurate technology at the time:
http://en.wikipedia.org/wiki/Washington_meridian
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<<The Ball Drop in Times Square stems from an even older ritual in England when a descending Time Ball was a popular method of signaling noon to allow pocket watches and nearby at sea ships chronometer's to be reset daily. This tradition continues onward today in Washington D.C. at the United States Naval Observatory where it still drops a Time Ball down a flag pole every day at noon.>>
http://www.usno.navy.mil/millennium/tball_hist.shtml

[interstellaryeller]

Thanks folks that is what I supected. the contellations will shift north which means ursa major and a few others will drop in declination. I thank you for your valued opinions on this thread.

[Chris Peterson]

Thanks folks that is what I supected. the contellations will shift north which means ursa major and a few others will drop in declination. I thank you for your valued opinions on this thread.

While I suspect you do have a proper visual for this, it isn't correct to say that the constellations will shift north. As the position of the pole shifts on the celestial sphere (which is a continuous process, of course), the coordinates of every point change as well. That is, the coordinates of every star (and constellation) are constantly changing. Depending on location, that change may be towards north (declination increasing), or away from it (declination decreasing). Star catalogs are always out of date. They normally have their coordinates defined on 50-year boundaries. In order to actually point at a catalog object, it is necessary to apply a mathematical transform to adjust the coordinates to the current time. Most catalogs are currently 2000.0, although some remain 1950.0. And the constellation boundaries are officially defined against 1875 coordinates.

[aristarchusinexile]

Summer in the northern hemisphere six years from now will be vastly different from today. The latest authoritative scientific word is that the arctic will be free of summer ice in six years.