Terrestrial Time is a theoretical uniform time scale, defined to provide continuity with the former Ephemeris Time ( ET ).

ET was an independent time-variable, proposed ( and its adoption agreed ) in the period 1948 – 52 with the intent of forming a gravitationally uniform time scale as far as was feasible at that time, and depending for its definition on Simon Newcomb's Tables of the Sun ( 1895 ), interpreted in a new way to accommodate certain observed discrepancies.

Newcomb's tables formed the basis of all astronomical ephemerides of the Sun from 1900 through 1983: they were originally expressed ( and published ) in terms of Greenwich Mean Time and the mean solar day, but later, in respect of the period 1960 – 1983, they were treated as expressed in terms of ET, in accordance with the adopted ET proposal of 1948 – 52.

The term ephemeris time ( often abbreviated ET ) can in principle refer to time in connection with any astronomical ephemeris.

Close equality between the ET second with the later SI second ( as defined with reference to the cesium atomic clock ) has been verified to within 1 part in 10 < sup > 10 </ sup >.

These measurements can be considered as secondary realizations ( in a metrological sense ) of the primary definition of ET in terms of the solar motion, after a calibration of the mean motion of the Moon with respect to the mean motion of the Sun.

Such secondary realizations were used and described as ' ET ', with an awareness that the time scales based on the atomic clocks were not identical to that defined by the primary ephemeris time standard, but rather, an improvement over it on account of their closer approximation to uniformity.

The atomic clocks gave rise to the atomic time scale, and to what was first called Terrestrial Dynamical Time and is now Terrestrial Time, defined to provide continuity with ET.

The availability of atomic clocks, together with the increasing accuracy of astronomical observations ( which meant that relativistic corrections were at least in the foreseeable future no longer going to be small enough to be neglected ), led to the eventual replacement of the ephemeris time standard by more refined time scales including terrestrial time and barycentric dynamical time, to which ET can be seen as an approximation.

In addition to these motor problems, a variety of non-motor features have recently been linked with ET.

Recent studies have demonstrated that late-onset ET ( onset > age 65 ) may be associated with an increased risk of developing dementia.

ET is one of the most common neurological diseases, with a prevalence of approximately 4 % in persons age 40 and older and considerably higher among persons in their 60s, 70s, 80s, and 90s.

In disabling cases, ET can interfere with a person's ability to perform tasks of daily living, including feeding, dressing, and activities of personal hygiene.

People with ET can sometimes have problems with word finding and can't articulate themselves effectively even with preparation.

A person with ET may become shy, withdrawn, pessimistic, anxious and also have difficulties concentrating.

It is common for those with ET to be embarrassed by the condition even though it is out of their control.

Recent postmortem studies have demonstrated the presence of degenerative changes in the ET brain, with these changes including Purkinje cell axonal swellings and Purkinje cell loss in the majority of cases and brainstem Lewy bodies in the remainder.

ET does sometimes occur in combination with other neurological disorders such as dystonia.

In addition, there may be a link between ET and Parkinson's disease, with one study showing ET patients having an approximately 4 times greater likelihood of developing Parkinson's disease.

Minor cases of ET can be treated with physical therapy and development of the muscles in the sections of the body that are severe in their shaking.

If the doubleheader network's games all finish before 7: 30 ET, it is supposed to conclude the post-game show within 10 minutes to protect NBC's pre-game show.

Although the show returned for the 1958 – 1959 season ( 5: 30 to 6: 00 pm ET ), these programs were repeats from the first two seasons, re-cut into a half-hour format.

The show premiered on September 19, 1983 on CBS at 10: 30 AM ET ( 9: 30 CT / MT / PT ), replacing Child's Play, and placing it between The New $ 25, 000 Pyramid and The Price Is Right.

NBC executives hoped to get Carvey to take over the 12: 30 a. m. ( ET ) weeknight spot in the network's lineup in 1993 when David Letterman left his show, Late Night with David Letterman, for an 11: 30 p. m. ( ET ) show on CBS.

Nickelodeon and its sister channels Nick Jr., TeenNick and Nicktoons ( along with some international versions of the channel ) suspend programming for three hours from 12 – 3 p. m. ET / PT on a Saturday afternoon in late September ( since 2005 ) during the event and show their testcards instead, and the respective websites of all four Nickelodeon channels are taken offline during that same three-hour time period.

At the same time the localised version that was previously produced stopped and was replaced with an edited version of the 2am ET show from Los Angeles, cut to fit 45 minutes through removing commercial breaks and stories on European sports such as soccer.

ET talk show, " Live With Dan Abrams ".

As of the beginning of May 2010, VH1 has permanently retire the named Nocturnal State and had temporarily cancelled the 5AM ET hour of Jump Start to make room for more reality show re-airs.

ET beginning on January 8, 2013, putting the show in direct competition with The Tonight Show, the Late Show with David Letterman, The Colbert Report and Conan.

In 1940, Allen moved back to CBS Radio with a new sponsor and show name, Texaco Star Theater airing every Wednesday at 9: 00 pm ET on CBS, then Sundays at 9: 00 pm in the fall of 1941.

By 1942, he shortened the show to half an hour, at 9: 30 pm ET – under network and sponsor edict, not his own.

NBC signed Leno to a new deal for a nightly talk show in the 10: 00 pm ET timeslot.

The show feeds live from 05: 00 to 09: 00 ET, with feeds and updates as required until noon.

The show is fed live weekdays at 12: 00 noon ET.

The third season of the show, titled simply Just for Laughs, began airing on June 21, 2009 at 7: 00 pm ET.

This happened a month after G4 moved the show to its earliest and least-viewed time slot, 9am ET weekdays.

The Clark Howard Show show on HLN runs every Saturday and Sunday at 6: 00 am, noon and 4: 00 pm ET.

For the first two seasons, the show was aired on Wednesday nights at 8pm ET / 7pm CT, to moderate ratings.

HSN Today is a morning show that airs weekdays from 6-9am ( ET ) and weekends from 7-9am ( ET ).

ET, switching with SportsCenter Monday Kickoff, all programs were moved to the Bristol studio, and the second version's hosts ( see below ) were also assigned to the earlier show.

ET, to compete directly with Rush Limbaugh, whose show is broadcast in that time slot also.