BEGIN:VCALENDAR VERSION:2.0 PRODID:-//InvisionCommunity Events 4.7.23//EN METHOD:PUBLISH CALSCALE:GREGORIAN REFRESH-INTERVAL:PT15M X-PUBLISHED-TTL:PT15M X-WR-CALNAME:RMCommunityCalendar NAME:RMCommunityCalendar BEGIN:VTIMEZONE TZID:Europe/London TZURL:http://tzurl.org/zoneinfo/Europe/London X-LIC-LOCATION:Europe/London BEGIN:DAYLIGHT TZOFFSETFROM:+0000 TZOFFSETTO:+0100 TZNAME:BST DTSTART:20260329T020000Z RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=-1SU END:DAYLIGHT BEGIN:STANDARD TZOFFSETFROM:+0100 TZOFFSETTO:+0000 TZNAME:GMT DTSTART:20261025T020000Z RRULE:FREQ=YEARLY;BYMONTH=10;BYDAY=-1SU END:STANDARD END:VTIMEZONE BEGIN:VEVENT SUMMARY:Perihelion + Aphelion explanation DTSTAMP:20251206T163220Z SEQUENCE:0 UID:607-7-c3fe8195a3dde498d013e477e2142422@aalbc.com ORGANIZER;CN="richardmurray":troy@aalbc.com DESCRIPTION:\n DATES or GRAPHIC\n\n\n\n \n\n\n\n Note: Distances are app roximate and calculated from JPL ephemeris data.\n\n\n\n \n\n\n\n \n\n\n\n Pluto is a dwarf planet. Its eccentricity causes it to cross Neptune’s orbit.\n\n\n\n TEXT\n\n\n\n  \n\n\n\n In astronomy\, perihelion and ap helion are the two extreme points in Earth’s elliptical orbit around th e Sun. These terms also apply to any object orbiting the Sun or another st ar. Perihelion is the point where the object is nearest to the Sun\, while aphelion is when it is farthest away. Earth’s orbit is not a perfect c ircle but a slightly flattened ellipse\, with the Sun at one of the foci of the ellipse (not the exact center)\, so the distance between Earth and the Sun varies slightly over the year.\n\n\n\n Although these points influ ence the amount of solar radiation Earth receives\, they are not responsib le for the seasons. Seasons arise from Earth’s axial tilt\, not its dis tance from the Sun. However\, the elliptical shape and the timing of perih elion and aphelion do subtly affect seasonal duration and intensity.\n\n\n \n Apsis is the general term for orbital extremes (includes perigee an d apogee for Earth-orbiting objects).\n\n\n\n  \n\n\n\n What Are Perihe lion and Aphelion?\n\n\n\n Johannes Kepler coined the terms “perihelio n” and “aphelion” to describe the orbits of planets around the Sun.\ n\n\n\n Perihelion: The point in a planet’s orbit where it is nearest to the Sun.\n\n\n\n Aphelion: The point in the orbit where the planet is far thest from the Sun.\n\n\n\n These distances are measured from the center o f the Sun to the center of the planet. The Earth is about 147.1 million k m (91.4 million mi) from the Sun at perihelion and about 152.1 million k m (94.5 million mi) at aphelion.\n\n\n\n Etymology\n\n\n\n Perihelion co mes from the Greek peri- (near) and helios (Sun).\n\n\n\n Aphelion co mes from apo- (away from) and helios (Sun).\n\n\n\n Both terms use the suffix -helion from the Greek word for Sun and are specific to objects orbiting the Sun. The more general term\, apsis\, refers to extreme point s in any orbital system.\n\n\n\n Apsis and Earth’s Orbit\n\n\n\n Althoug h Earth’s orbit is elliptical\, the Sun is not located at the center o f the ellipse. Instead\, it occupies one of the two focal points of the orbit\, while the other focus lies in empty space. This means Earth–Sun distance changes slightly throughout the year\, giving rise to perihelion and aphelion.\n\n\n\n The line of apsides connects the perihelion and ap helion of an orbit. For Earth\, the apsides shift over time due to gravi tational interactions with the Moon and planets\, causing apsidal prece ssion.\n\n\n\n Although Earth’s orbit is almost circular\, the slight el liptical shape leads to small but measurable differences in solar distance during the year. These points of apsis don’t align with solstices or  equinoxes due to this precession.\n\n\n\n Eccentricity and Orbital Shap e\n\n\n\n Eccentricity (e) describes how much an orbit deviates from a pe rfect circle:\n\n\n\n A circle has eccentricity e = 0.\n\n\n\n Ellipses h ave 0 <\; e <\; 1.\n\n\n\n Earth’s current orbital eccentricity is about 0.0167\, meaning it’s very close to circular. In graphics\, illus trators exaggerate the ellipse to convey that the orbit is not a perfect c ircle.\n\n\n\n Over tens of thousands of years\, Earth’s eccentricity va ries due to gravitational interactions\, influencing climate cycles (Milan kovitch cycles).\n\n\n\n Do Perihelion or Aphelion Coincide With Solstices or Equinoxes?\n\n\n\n Currently\, perihelion occurs shortly after the De cember solstice\, and aphelion occurs after the June solstice. The proxim ity of perihelion to the Northern Hemisphere’s winter solstice slightl y shortens winter and lengthens summer.\n\n\n\n Due to apsidal precession \, these dates shift by about one day every 58 years. Around the year 1246 \, perihelion occurred on the December solstice. In about 10\,000 years\, it will coincide with the March equinox.\n\n\n\n Apsis and the Seasons\n\ n\n\n While it’s common to assume that Earth’s varying distance from t he Sun causes the seasons\, this is not the case. The primary driver of se asonal change is Earth’s axial tilt of about 23.5°\, not its distance from the Sun. However\, the location of the apsides (perihelion and aphel ion) does have subtle effects on seasonal length and solar intensity.\n\n \n\n At perihelion\, Earth is closest to the Sun and moves faster in it s orbit due to the increased gravitational pull. As a result\, the Northe rn Hemisphere winter is slightly shorter (about 89 days)\, while summer i s slightly longer (about 93 days). The opposite occurs in the Southern Hem isphere\, which receives more intense solar radiation during its shorter s ummer because of Earth’s proximity to the Sun at that time.\n\n\n\n The uneven distribution of land and ocean between the hemispheres enhances thi s asymmetry. The Southern Hemisphere has more ocean\, which moderates tem perature changes\, while the Northern Hemisphere has more landmass and ex periences greater seasonal variation despite receiving slightly less sunli ght at aphelion.\n\n\n\n Apsidal Precession and Milankovitch Cycles\n\n\n\ n Over thousands of years\, the orientation of Earth’s orbit gradually s hifts due to apsidal precession\, a slow rotation of the line connecting perihelion and aphelion. Currently\, Earth reaches perihelion shortly aft er the December solstice\, but this alignment drifts forward through the c alendar over time.\n\n\n\n This precession completes a full cycle approxim ately every 112\,000 to 130\,000 years. As a result\, the timing of perih elion slowly changes in relation to the equinoxes and solstices. When peri helion occurs during a Northern Hemisphere summer\, the hemispheric season al differences are minimized. When it aligns with winter\, the seasonal co ntrast is enhanced.\n\n\n\n Apsidal precession is one of the three key orb ital variations described by Milutin Milankovitch\, which influence long- term climate cycles on Earth:\n\n\n\n Eccentricity – the shape of Ear th’s orbit (100\,000-year cycle)\n\n\n\n Axial tilt (obliquity) – the angle of Earth’s axis (41\,000-year cycle)\n\n\n\n Precession – the wobble of Earth’s axis (26\,000-year cycle)\n\n\n\n Together\, these Mi lankovitch cycles affect Earth’s climate patterns and have been linked to the timing of ice ages and interglacial periods.\n\n\n\n Perigee and Ap ogee: Apsis Terms for Earth-Orbiting Bodies\n\n\n\n The -helion suffix r efers to a body orbiting the Sun\, while the -gee suffix refers to the a psis of a body orbiting Earth.\n\n\n\n Perigee: Closest point to Earth in the orbit of a satellite or the Moon.\n\n\n\n Apogee: Farthest point from Earth.\n\n\n\n These are the equivalents of perihelion and aphelion for or bits around the Earth.\n\n\n\n For example:\n\n\n\n The Moon reaches perig ee at about 363\,300 km and apogee at about 405\,500 km.\n\n\n\n These distances affect apparent size (e.g.\, supermoons at perigee) and gravitat ional effects.\n\n\n\n Comparison With Binary Star Systems or Exoplanets\n \n\n\n The concept of apsis also applies to planets orbiting other stars o r star system. For exoplanets (planets outside our Solar System)\, the t erms periastron and apastron are the general terms for orbiting stars . In binary star systems\, the terms periastron and apastron describe the closest and farthest points in the orbit of one star around another.\n\n\ n\n Understanding their orbital eccentricity and distance variation aids i n evaluating the planet’s habitability\, particularly if large differenc es in distance lead to extreme temperature swings.\n\n\n\n Some exoplanets \, known as eccentric Jupiters\, have highly elliptical orbits that cause drastic changes in their environment as they swing close to and far from their stars. In contrast\, planets with low eccentricity and stable distan ces from their stars are more likely to support Earth-like conditions.\n\n \n\n In summary\, astronomers use periapsis terminology that describes the central body:\n\n\n\n Perihelion/aphelion – around the Sun\n\n\n\n Per igee/apogee – around Earth\n\n\n\n Periastron/apastron – around anot her star\n\n\n\n Perijove/apojove – around Jupiter\n\n\n\n Kepler’s L aws in Context\n\n\n\n Kepler’s Laws of Planetary Motion describe the m echanics of elliptical orbits\, including the behavior of perihelion and a phelion:\n\n\n\n Law of Ellipses\n\n Each planet orbits the Sun in an ell ipse with the Sun at one focus (not the center). This explains why Earth has both a closest and farthest point in its orbit.\n\n\n\n Law of Equal A reas\n\n A line joining a planet and the Sun sweeps out equal areas in eq ual time. This means Earth moves faster at perihelion and slower at aph elion\, altering the apparent speed of the seasons.\n\n\n\n Law of Harmoni es\n\n The square of a planet’s orbital period is proportional to the cu be of its semi-major axis:\n\n T2 ∝ a3\n\n This law relates orbital dur ation and distance\, and helps astronomers compare orbits across the Solar System.\n\n\n\n Kepler’s laws form the foundation for Newton’s laws of motion and universal gravitation\, and they remain essential for calcu lating orbits\, planning space missions\, and understanding the celestial mechanics of planets and moons.\n\n\n\n FAQs About Perihelion and Aphelion \n\n\n\n Q: Does perihelion make Earth hotter?\n\n A: No\, seasons are co ntrolled by axial tilt\, not proximity to the Sun. However\, perihelion do es slightly increase solar radiation\, particularly in the Southern Hemisp here.\n\n\n\n Q: Why isn’t Earth warmest at perihelion?\n\n A: The Nort hern Hemisphere\, which has more landmass\, tilts away from the Sun during perihelion. Land heats and cools more rapidly than oceans\, so Southern H emisphere summers are slightly milder.\n\n\n\n Q: Is Earth speeding up or slowing down at perihelion?\n\n A: Earth moves faster at perihelion an d slower at aphelion\, as predicted by Kepler’s second law (equal are as in equal time).\n\n\n\n Q: Can perihelion and solstice happen on the sa me day?\n\n A: Yes\, but it’s rare. The last near-alignment was in 1246 CE. They drift apart due to apsidal precession.\n\n\n\n Q: Is the orbit g etting more or less eccentric?\n\n A: Eccentricity varies cyclically (~10 0\,000-year cycles). Currently\, Earth’s orbit is becoming slightly le ss eccentric.\n\n\n\n Q: What is the difference between perihelion and pe rigee?\n\n A: Perihelion refers to being closest to the Sun. Perigee r efers to being closest to Earth in a satellite’s orbit.\n\n\n\n Referenc es\n\n\n\n D’Eliseo\, Maurizio M.\; Mironov\, Sergey V. (2009). “The G ravitational Ellipse”. Journal of Mathematical Physics. 50 (2): 022901. doi:10.1063/1.3078419\n\n\n\n Luo\, Siwei (2020). “The Sturm-Liouville problem of two-body system”. Journal of Physics Communications. 4 (6): 061001. doi:10.1088/2399-6528/ab9c30\n\n\n\n Michelsen\, Neil F. (1982).  The American Ephemeris for the 21st Century – 2001 to 2100 at Midnight. Astro Computing Services. ISBN 0-917086-50-3.\n\n\n\n REFERAL\n\n\n\n http s://sciencenotes.org/perihelion-and-aphelion-closest-and-farthest-points-f rom-the-sun/\n\n DTSTART;VALUE=DATE:20260101 RRULE:FREQ=YEARLY;INTERVAL=1 END:VEVENT END:VCALENDAR