By Glenn A. Walsh
Reporting for SpaceWatchtower
We are now entering the “Dog Days of Summer” in Earth's Northern Hemisphere. However, this is also the time of year, shortly after the Northern Hemisphere's Summer Solstice, when the Earth is actually farthest from the Sun (known as Earth Aphelion) !
Today, the Dog Days of Summer are considered the days between July 3 and August 11 each year. These Dog Days begin just a little less than two weeks after the Summer Solstice, the official beginning of Summer in the Northern Hemisphere.
For A.D. 2024, the season of Summer began at Earth's Northern Hemisphere's Summer Solstice (and the season of Winter begins at the Southern Hemisphere's Winter Solstice) at the moment of the June Solstice: Thursday Afternoon, 2024 June 20 at 4:51 p.m. Eastern Daylight Saving Time (EDT) / 20:51 Coordinated Universal Time [UTC – International time used by scientists; previously referred to as Greenwich Mean Time (GMT) or Greenwich Civil Time (GCT)]. Summer will continue in the Northern Hemisphere (and Winter will continue in the Southern Hemisphere) until the Autumnal Equinox when the season of Autumn / Fall commences in the Northern Hemisphere (and Spring begins in the Southern Hemisphere): Sunday Morning, 2024 September 22 at 8:44 a.m. EDT / 12:44 UTC.
In Meteorology (Weather Science), the convention is to start a season on the first day of a calendar month. So, Meteorological Summer runs from June 1 to August 31.
Also within the Dog Days of Summer come the traditional Cross-Quarter (XQ) Day known as Lammas (Anglo-Saxon) or Lughnasadh (Irish / Scottish) on August 1. Located approximately half-way between the Summer Solstice and the Autumnal Equinox, this day has long been considered the beginning of harvesting crops.
Lammas / Lughnasadh Day, in ancient times,was a festival day which marked the start of the harvest season, particularly the wheat harvest. On Lammas Day, it was customary to bring a loaf of bread, from the new crop, to church to be blessed.
August 1 also marks the anniversary of the birth of America's first professional, female astronomer. Maria Mitchell, Professor of Astronomy at Vassar College and discoverer of Miss Mitchell's Comet in 1847, was born on 1818 August 1 in Nantucket, Massachusetts.
While August 1 is the traditional Cross-Quarter Day, due to calendar changes over the years, in modern times the actual Cross-Quarter Day differs by as much as a week. For 2024, Lammas / Lughnasadh Day actually occurs on Tuesday, 2024 August 6 at 8:10 p.m. EDT / August 7 at 0:10 UTC.
Dog Days of Summer
So, how did these days become known as the Dog Days of Summer?
First, we need to look at the pictures in the sky that ancient peoples saw in the stars, now known as constellations. One of the most recognized constellations is that of Orion the Hunter (Ori).
And, many hunters have one or more hunting dogs to assist them. This was also true in Greek mythology for Orion. Orion's two dogs, Canis Majoris or Canis Major (CMa: Greater Dog) and Canis Minoris Canis Minor (CMi: Lesser Dog), were each given their own constellation.
The brightest star in Canis Major also happens to be the brightest star in Earth's night sky, the star Sirius (Alpha CMa or a CMa). And, being the brightest star in Canis Major, Sirius is known as the “Dog Star”. Sirius is located 8.611 light-years from the Earth and has an astronomical, Apparent Visual Magnitude of brightness of -1.45.
Being the brightest star in the night sky, ancient Romans assumed that Sirius provided heat to the Earth, as did our Solar System's Sun. During the Summer months, Sirius rises and sets at generally the same time as our Sun. Even in ancient times, astronomers were able to use mathematics to determine the rising and setting times of a star in the daytime sky.
The Romans believed that heat from Sirius, added to the heat from the Sun, caused the Summer months to be so much hotter than the rest of the year. Hence, the middle of the Summer season in Earth's Northern Hemisphere, now during July 3 to August 11 (the actual dates varied, somewhat, in ancient times), has become known as the Dog Days of Summer.
Today, we realize that a star 8.611 light-years away, no matter how bright, can never provide enough heat to affect life on Earth. Further, even the annual, variable distance between Earth and our own Sun is not the reason for the additional heat in the Northern Hemisphere during the Summer months.
Earth Aphelion
Although the Summer months in the Northern Hemisphere are known for the year's warmest weather, the Earth is actually at the point in its orbit farthest from the Sun (astronomically known as the point of Aphelion) around July 5. This Friday morning, just one day after the day we celebrate the 248th year of American Independence on July 4 and a couple weeks after the Summer Solstice on June 20, will mark Aphelion for 2024, the location in Earth's annual orbit around the Sun where our planet is farthest from the Sun for the entire year!
This year, Earth Aphelion will occur early on Friday Morning, 2024 July 5 at 1:06 a.m. Eastern Daylight Saving Time (EDT) / 5:06 Coordinated Universal Time [UTC – International time used by scientists; previously referred to as Greenwich Mean Time (GMT) or Greenwich Civil Time (GCT)]. At that moment, Earth will be the farthest from the Sun for the whole year: 94,510,539 statute miles / 152,099,968 kilometers.
Earth's closest approach to the Sun this year (known astronomically as Perihelion) occurred on 2024 January 2 at 7:38 p.m. Eastern Standard Time (EST) / January 3 at 0:38 UTC, at a distance of 91,404,095 statute miles / 147100631.86 kilometers. Next year, Perihelion occurs on 2025 January 4 at 8:28 a.m. EST / 13:28 UTC, at a distance of 91,405,993 statute miles / 147103686.4 kilometers.
In general, the distance from the Earth to the Sun is not the major factor determining the heat of Summer or the cold of Winter. This is true, despite the fact that Earth receives about 7 per-cent more solar radiation from the Sun during the time of Earth Perihelion in January, than at the time of Earth Aphelion in July.
Solar radiation, and hence the heat from the Sun, depends on the length of daylight and the angle of the Sun above the horizon. The tilt of the planet's axis, about 23.44 degrees toward the Sun, determines the additional and more direct solar radiation received by a planet's Northern or Southern Hemisphere, and hence, the warmer season of the respective hemisphere.
While the Sun does have motions (the Sun rotates on its own axis about once every 27 Earth days; our Solar System revolves around the center of the Milky Way Galaxy once every 225 million-to-250 million Earth years), it is actually the motion of the Earth tilted on its axis, away from the plane of the ecliptic (Earth's orbital plane around the Sun), while revolving around the Sun, that causes the Earth's seasons.
The Earth's Perihelion in January, and Aphelion in July, are due to the elliptical nature of the Earth's orbit around the Sun. Perihelion and Aphelion would not occur if the Earth's orbit was a true circle.
The dates of Earth Perihelion and Earth Aphelion are not fixed. Due to the Earth's Precession of the Equinoxes, these days shift forward approximately one day every 58 years. About 800 years ago, the Earth Perihelion was on the date of the Winter Solstice, around December 21; Earth Perihelion will be on the Vernal Equinox, the beginning of Spring around March 20, about 4,300 years from now. Earth's Axial Precession (often described as a "wobble" in the Earth's orientation, like a spinning top or a gyroscope) gradually changes the orientation of the Earth's Rotational Axis, which completes one rotational cycle once every 25,772 years.
However, because Earth is farther from the Sun during our Spring and Summer seasons, people in Earth's Northern Hemisphere actually benefit from a few extra days of warmth (on average), than the number of days in the Autumn and Winter seasons of the year. When Earth is closer to the Sun, the Earth travels faster in its elliptical orbit around the Sun (during the Autumn and Winter months); and, when Earth is farther than average from the Sun (during the Spring and Summer seasons) the Earth travels a little more slowly (Kepler's Second Law of Planetary Motion) --- again, this refers to the Northern Hemisphere. Hence, the Spring and Summer seasons, in the Northern Hemisphere, have a few more days than the Autumn and Winter seasons.
In fact, the late Jay Pasachoff, who was Field Memorial Professor of Astronomy at Williams College in Williamstown, Massachusetts and author of widely-used, college astronomy text-books, precisely calculated the duration of each season in the Northern Hemisphere:
* Summer: 93 days, 15 hours
* Spring: 92 days, 19 hours
* Autumn / Fall: 89 days, 20 hours
* Winter: 89 days, 0 hours
Internet Links to Additional Information ---
Dog Days of Summer -
Link 1 >>> https://wilstar.com/dogdays/
Link 2 >>> https://en.wikipedia.org/wiki/Dog_days
Star Sirius: Link >>> https://en.wikipedia.org/wiki/Sirius
Constellation Canis Major: Link >>> https://en.wikipedia.org/wiki/Canis_Major
Science Experiments Children & Teens Can Do At Home During Summer Break !
"Summer Begins Thursday Afternoon at Solstice." Mon., 2024 June 17.
"Earth Farthest from Sun for Year: Thursday." Mon., 2023 July 3.
1st U.S. Female Professional Astronomer: Leading Women's Suffragist." Wed., 2020 Aug. 26.
"Astronomical Mid-Point of Summer." Tue., 2013 July 30.
Source: Glenn A. Walsh Reporting for SpaceWatchtower, a project of Friends of the Zeiss
"Dog Days of Summer Begin, As Earth Farthest from Sun!"
Wednesday, 2024 July 3.
Artificial Intelligence not used in the writing or production of this article.
© Copyright 2024 Glenn A. Walsh, All Rights Reserved
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Glenn A. Walsh, Informal Science Educator & Communicator (For more than 50 years! - Since Monday Morning, 1972 June 12):
Link >>> http://buhlplanetarium2.tripod.com/weblog/spacewatchtower/gaw/
Electronic Mail: < gawalsh@planetarium.cc >
Project Director, Friends of the Zeiss: Link >>> http://buhlplanetarium.tripod.com/fotz/
SpaceWatchtower Editor / Author: Link >>> http://spacewatchtower.blogspot.com/
Formerly Astronomical Observatory Coordinator & Planetarium Lecturer, original Buhl Planetarium & Institute of Popular Science (a.k.a. Buhl Science Center), America's fifth major planetarium and Pittsburgh's science & technology museum from 1939 to 1991.
Formerly Trustee, Andrew Carnegie Free Library and Music Hall, Pittsburgh suburb of Carnegie, Pennsylvania, the fourth of only five libraries where both construction and endowment funded by famous industrialist & philanthropist Andrew Carnegie.
Author of History Web Sites on the Internet --
* Buhl Planetarium, Pittsburgh: Link >>> http://www.planetarium.cc Buhl Observatory: Link >>> http://spacewatchtower.blogspot.com/2016/11/75th-anniversary-americas-5th-public.html
* Adler Planetarium, Chicago: Link >>> http://adlerplanetarium.tripod.com
* Astronomer, Educator, Optician John A. Brashear: Link >>> http://johnbrashear.tripod.com
* Andrew Carnegie & Carnegie Libraries: Link >>> http://www.andrewcarnegie.cc
* Other Walsh-Authored Blog & Web-Sites: Link >>> https://buhlplanetarium.tripod.com/gawweb.html
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