Astronomy for PSP

Astronomy for PSP
Astronomy for PSP
General
Author	HarPet Programming Group
Type	Other
Version	4.3
License	Mixed
Last Updated	2009/06/21
Links
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An astronomical program that can display: Julian day, Eastern Day, Position of sun, moon, planets, minorplanets and comets Perihelion, Aphelion time of the planets, Sun and moon eclipses, Local Sun eclipse, Phases Moon, Jupiter Moons, Saturn Moons, Equinox, Star Chart, Position Planets, Planets Move.

User guide

True Solar Time

True solar time is based on the solar day, which is the time between one solar noon and the next. A solar day is roughly 24 hours, but because Earth's orbit around the Sun is elliptical and varies by location, solar time can differ by up to 15 minutes from the standard time. There are also slight changes due to Earth's wobble, but these variations are very small, usually less than a second per year.

Sidereal Time

Sidereal time is time measured by the stars. A sidereal day is the time it takes Earth to complete one full rotation relative to the stars, which is approximately 23 hours, 56 minutes, and 4 seconds. Since stars move slightly over time, sidereal time can't be used as a consistent time standard, as it depends on which star you are using as a reference.

Greenwich Mean Time (GMT)

Greenwich Mean Time is the time based on the Prime Meridian in Greenwich, England (0° longitude). It was historically derived from true solar time, with a correction known as the "equation of time" to smooth out the irregularities caused by Earth's elliptical orbit and the tilt of its axis. GMT used to be the international time standard, but it has been replaced by more precise atomic clocks. Although GMT no longer serves as an official time standard, the term is still sometimes used interchangeably with Universal Time (UT). GMT is also still used to refer to the time zone of the Prime Meridian.

Universal Time (UT)

Universal Time is a time scale based on the mean solar day and aims to be as uniform as possible, despite irregularities in Earth's rotation. There are different types of Universal Time:

UT0: The rotational time at a specific location, observed through the motion of stars or extraterrestrial radio sources.
UT1: A version of UT0 that accounts for the effect of Earth's polar motion on the observer’s longitude. It varies slightly due to irregularities in Earth's rotation.

Ephemeris Time (ET)

Ephemeris Time was an obsolete time standard based on the "ephemeris second," which was a fraction of the tropical year. It was used from 1956 to 1967 as the basis for the SI second but was discontinued in 1984.

Ephemeris Time was replaced by "TDT" (which later became "TT"), and for astronomical purposes, it was replaced by "TDB" (Barycentric Dynamical Time) and "TCB" (Barycentric Coordinate Time). These are used for calculating time in the solar system. For Earth-based calculations, TCG (Geocentric Coordinate Time) is used instead.

Julian Day Number

The Julian Day Number is a continuous count of days starting from Greenwich mean noon on January 1, 4713 B.C. in the Julian proleptic calendar. The Julian Date is this number followed by the fraction of the day that has passed since noon. This system is especially useful for astronomers since it avoids the date skip during an observation night.

Easter Day

Easter falls on the first Sunday following the first ecclesiastical full moon that occurs on or after March 21 (the day of the ecclesiastical vernal equinox).

This particular ecclesiastical full moon is the 14th day of a tabular lunation (new moon).

Equinox

In astronomy, an equinox occurs when the Sun is directly above Earth's equator, which happens twice a year: around March 20 and September 22. On these dates, day and night are nearly equal in length, and the Sun crosses the celestial equator, marking the points of declination 0.

Perihelion / Aphelion

In astronomy, the term "apsis" refers to the points in an object's elliptical orbit that are either closest or farthest from its center of attraction, which is generally the center of mass of the system.

The point of closest approach is called the "periapsis" or "pericentre", and the point of farthest distance is called the "apoapsis."