This diagram shows the position of the Earth, in relation to the Sun, at the time of the Summer Solstice, as well as the Winter Solstice and the Spring and Autumnal Equinoxes of the year.
[Graphic Source: ©1999, Eric G. Canali, former Floor Operations Manager of the original Buhl Planetarium and Institute of Popular Science / Buhl Science Center (America's 5th major planetarium & Pittsburgh's science and technology museum from 1939 to 1991) and Founder of the South Hills Backyard Astronomers amateur astronomy club. Permission granted for non-profit use only, with credit to author.]
By
Glenn A. Walsh
Reporting
for SpaceWatchtower
Friday
night, Summer begins in the Northern Hemisphere of Earth, while at
the same time, Winter begins in the Southern Hemisphere.
For
A.D. 2025, the season of Summer begins 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: Friday Evening, 2025 June 20 at 10:42 p.m. Eastern Daylight
Saving Time (EDT) / June 21, 2:42 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): Monday Afternoon, 2025 September 22 at
2:19 p.m. EDT / 18:19 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.
In
Etymology, the word Solstice comes from the Latin
terms Sol (Sun) and Sistere (to
stand still). In ancient times, Astronomers / Astrologers / Priests
recognized that on one day of the year (in the Northern Hemisphere,
on or near the day we now call June 21), the Sun would appear to
stand-still (regarding the Sun's apparent move higher or
lower in the sky, from day-to-day) as Sol reaches its highest point
in the sky for the entire year. The motion of the Sun's apparent path
in the sky (daily motion higher or lower in the sky, what is known
astronomically, today, as the Sun's Declination) would
cease on this day, before appearing to reverse
direction.
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. The Earth's closest approach to the Sun (Perihelion)
each year is around January 2. Hence, 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
year, Earth Aphelion will occur early on Thursday Afternoon, 2025
July 3 at 4:00 p.m. EDT / 20:00 UTC. At that moment, Earth will be
the farthest from the Sun for the whole year: 94,502,714.14936769
statute miles / 152,087,376 kilometers.
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
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 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, but as a
sphere of hot plasma the rotation rate varies by Latitude (at the
Solar Equator - Sidereal Rotation Period: 24.47 Earth days, Synodic
Rotation Rate: 26.24 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.
Hence,
as the Earth arrives at the point in its orbit around the Sun, when
the north polar axis is most directly inclined toward the Sun, this
marks the Summer Solstice in the Northern Hemisphere and the Winter
Solstice in the Southern Hemisphere.
Alternately,
the Winter Solstice in the Northern Hemisphere (the Winter Solstice
is always on or near, what we now refer to as, December 21) occurs
when the Earth reaches the point in its orbit when the North Pole is
most directly inclined away from the Sun (and, the South Pole is most
directly inclined toward the Sun). And, conversely, at this time
Summer begins in the planet's Southern Hemisphere.
For
Earth observers at the North Latitude which matches the Earth's Axial
Tilt or Obliquity, at the moment of the June Solstice, the Sun will
appear to shine directly overhead. The line around the Earth at the
North Latitude which matches the Earth's Axial Tilt or Obliquity is
known as the Tropic of Cancer (a.k.a. Northern Tropic). Likewise, the
South Latitude which matches the Earth's Axial Tilt or Obliquity is
located at the Tropic of Capricorn (a.k.a. Southern Tropic), where
the Sun appears directly overhead at the moment of the December
Solstice.
However,
as the tilt of the Earth is dynamic, and changes minutely over the
years, the location of the Tropic lines also change. Currently, these
Tropic lines are moving north at the rate of 0.47 arc-seconds / 49.21
feet / 15 meters per year.
The
names Tropic of Cancer and Tropic of Capricorn were coined in the
last centuries B.C., when the Sun would appear in the Constellation
Cancer the Crab on the June Solstice and in the Constellation
Capricornus the Horned Goat on the December Solstice. However today,
hours after the June Solstice, the Sun enters the Constellation
Gemini the Twins, 30 degrees from Cancer. And at the December
Solstice, the Sun is now in the Constellation Sagittarius the Archer.
This
is due to “Precession of the Equinoxes” of Earth, which is
analogous to the wobbling of a spinning top. In the case of the
Earth, this 25,772-year wobble causes observers to view the Sun in
different parts of the sky over the centuries, at the same time of
year while remaining in the same geographical location. As the Earth
wobbles over the centuries, the North Pole Star also changes.
Currently, Polaris is our North Pole Star; around A.D. 13,700, Vega
will be our North Pole Star, due to the Precession of the Equinoxes.
No
matter which hemisphere, the day of the Summer Solstice always has
the most hours and minutes of daylight (the length of time between
Sunrise and Sunset) for the year, while the Winter Solstice always
has the least number of hours and minutes of daylight for the year.
The exact number of hours and minutes of daylight, for a particular
location, depends on the locale's geographic Latitude on the Earth.
Astronomers, amateur ("ham") radio operators, and
long-distance radio enthusiasts (“radio DXers”), all of whom
mostly depend on non-daylight hours to ply their craft, often prefer
the days closer to the Winter Solstice.
The
Vernal Equinox, when the season of Spring begins in the Northern
Hemisphere (and the season of Autumn begins in the Southern
Hemisphere), occurs between the Winter and Summer Solstices when the
Earth reaches the point in its orbit around the Sun when the Earth's
axis is inclined neither toward nor away from the Sun. Likewise, when
the Earth reaches the point in its orbit around the Sun, between the
Summer and Winter Solstices, when the Earth's axis is inclined
neither toward nor away from the Sun, this is known as the Autumnal
Equinox (beginning of Fall or Autumn) in the Northern Hemisphere; at
this time Spring begins in the Southern Hemisphere. And, half-way
between the beginning points of each season are Cross-Quarter Days,
each related to traditional holidays: Groundhog Day (February 2), May
Day (May 1), Lammas Day (traditionally, the first harvest festival of
the year on August 1), and Halloween (October 31).
In
ancient times, the Summer Solstice was known as Mid-Summer Day, in
early calendars observed around June 24. At that time, May 1 to
August 1 (i.e. the two Cross-Quarter Days) was considered the season
of Summer. Such early European celebrations were pre-Christian in
origin. Many will associate this ancient holiday with the famous
William Shakespeare play, “A Midsummer Night's Dream.” Some
speculate that the play was written for the Queen of England, to
celebrate the Feast Day of Saint John.
As
with the Roman Catholic Church's decision to Christianize the pagan
Winter Solstice festivals with the introduction of Christmas Day on
December 25 (by an early calendar, December 25 was reckoned as the
Winter Solstice), the Church began to associate the Mid-Summer
festivals with the Nativity of Saint John the Baptist on June 24. In
the Christian Bible, the Gospel of Saint Luke implies that Saint John
was born six months before the birth of Jesus, although no specific
birth dates are given.
The
most famous celebration of the Summer Solstice occurs each year at
the Stonehenge pre-historic monument in England. Constructed between
3,000 B.C. and 1,600 B.C. in three phases, the actual purpose of the
landmark is still unclear. However, it seems to have been associated
with burials, originally. It was also used as a type of astronomical
observatory, particularly for observing the Sun, which was important
to help early cultures make annual decisions regarding agriculture.
Stonehenge
is known as a way for pre-historic peoples to mark both the Summer
and Winter Solstices. From inside the monument, a viewer facing
northeast can watch the Sun rise (weather-permitting) above a stone
outside the main circle of rocks, known as the Heel Stone, on the day
of the Summer Solstice in the Northern Hemisphere. Although today,
due to serious erosion of the stones, visitors on the Summer Solstice
can only walk around the landmark from a short distance away during
this annual event.
Although
not as prominent as Stonehenge, a calendar ring using smaller rocks
was also constructed at Nabta Playa in southern Egypt, perhaps as
early as 7,000 years ago! As with Stonehenge, some stones aligned
with Sunrise on the day of the Summer Solstice.
Today,
a Stonehenge-like event occurs each year at the University of Wyoming
(UW) Art Museum in Laramie, Wyoming, free-of-charge to the general
public. At 12:00 Noon Mountain Daylight Saving Time (MDT) / 2:00 p.m.
EDT / 18:00 UTC on the day of the Summer Solstice, visitors can see a
single beam of sunlight shine through a solar tube in the ceiling of
the UW Art Museum's Rotunda Gallery; the beam of sunlight then shines
onto a 1923 Peace Silver Dollar embedded in the floor of the Museum's
Rotunda Gallery. Visitors are encouraged to arrive at the museum by
11:30 a.m. MDT / 1:30 p.m. EDT / 17:30 UTC, to view this rather
unique architectural feature.
The
bright Star Spica (Alpha Virginis), the brightest star in the
Constellation Virgo the Virgin and the 16th brightest
star in Earth's night sky (Apparent Visual Magnitude: + 0.97), may
have helped develop another one of civilization's early calendars.
A calendar of ancient Armenia used the year's first sighting of Spica
in the dawn sky, a few days before the Summer Solstice, to mark the
beginning of the New Year for this particular calendar. The
development of this calendar somewhat coincided with the beginning of
agriculture in Armenia.
Like
clock-work, a well-known asterism (pattern of stars in the sky, not
officially recognized as a constellation) of three stars shaped as a
triangle is visible nearly overhead around local midnight during the
Summer months (weather-permitting). And logically, as Star
Trek's Mr. Spock might say, this asterism is known as the Summer
Triangle!
Three
of the brightest stars in the Summer sky constitute the Summer
Triangle ---
Vega
(Alpha Lyrae - brightest star in the Constellation Lyra the Harp);
brightest of the three stars and closest to the zenith (highest
point in the sky);
Altair
(Alpha Aquilae - denotes the eagle eye and brightest star in the
Constellation Aquila the Eagle); second brightest star of the trio;
Deneb
(Alpha Cygni - denotes the tail star, is the brightest star in the
Constellation Cygnus the Swan, and is the “head” star of the
asterism known as the Northern Cross).
The
term Summer Triangle was popularized in the 1950s by American author
H.A. Rey and British astronomer Patrick Moore, although constellation
guidebooks mention this triangle of stars as far back as 1913. And,
during World War II, military navigators referred to this asterism as
the “Navigator's Triangle.”
Regardless
of city light pollution, the three bright stars of the Summer
Triangle should be visible to nearly everyone in Earth's Northern
Hemisphere (weather-permitting). So, just look overhead late-evening
or early-morning throughout the Summer for these annual visitors to
our Summer sky!
Internet Links to Additional Information ---
Axial Tilt / Obliquity:
Link 1 >>> https://www.timeanddate.com/astronomy/axial-tilt-obliquity.html
Link 2 >>> https://en.wikipedia.org/wiki/Axial_tilt
Summer Solstice:
Link 1 >>> http://scienceworld.wolfram.com/astronomy/SummerSolstice.html
Link 2 >>> http://en.wikipedia.org/wiki/Summer_solstice
Season of Summer: Link >>> http://en.wikipedia.org/wiki/Summer
History of Mid-Summer: Link >>> http://en.wikipedia.org/wiki/Midsummer
Summer "Solstice Day" Annual Free-of-Charge Day (With Snowballs !), 1985 to 1991, at the original Buhl Planetarium and Institute of Popular Science (a.k.a. Buhl Science Center), America's 5th Major Planetarium and Pittsburgh's science and technology museum from 1939 to 1991:
Link >>> http://spacewatchtower.blogspot.com/2015/06/snowballs-on-first-day-of-summer.html
Stonehenge: Link >>> https://en.wikipedia.org/wiki/Stonehenge
Star Spica: Link >>> https://en.wikipedia.org/wiki/Spica
Precession of the Equinoxes: Link >>> https://en.wikipedia.org/wiki/Axial_precession
Tropic of Cancer: Link >>> https://en.wikipedia.org/wiki/Tropic_of_Cancer
Tropic of Capricorn: Link >>> https://en.wikipedia.org/wiki/Tropic_of_Capricorn
Summer Triangle: Link >>> https://en.wikipedia.org/wiki/Summer_Triangle
Science Experiments Children & Teens Can Do At Home During Summer Break !
Source: Glenn A. Walsh Reporting for SpaceWatchtower, a project of Foriends of the Zeiss
"Summer Begins at Solstice Friday Night"
Wednesday, 2025 June 18.
Artificial Intelligence not used in the writing or production of this article.
© Copyright 2025 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
