The “Dog Days” of summer have arrived. This popular saying refers to what are traditionally the hottest and most oppressive days of the season.
Rooted in astronomy, the phrase is linked to Sirius, the brightest star seen from Earth. As part of the constellation Canis Major, it is known as the Dog Star. During most of July and August, Sirius rises and sets with our Sun. Ancient Greeks and Romans believed it acted like a second Sun, adding extra heat to summer days. Today, we know that light from this distant star does not affect our weather, but the name has endured.
Varying by latitude around the globe, the so-called “Dog Days” of summer typically run from July 3 to August 11 in the United States.
Sirius, the “Dog Star”. Credit: EarthSky/Tom Wildoner
The Earth will reach its farthest point from the Sun today – an event known as the aphelion. It will officially take place at 20:11 UTC, which is 4:11 PM Eastern Daylight Time.
This annual event is a result of the elliptical shape of the Earth’s orbit and the slightly off-centered position of the Sun inside that path. The exact date of the Aphelion differs from year to year, but it’s usually in early July – summer in the northern hemisphere.
While the planet’s distance from the Sun is not responsible for the seasons, it does influence their length. As a function of gravity, the closer the planet is to the Sun, the faster it moves. Today, Earth is about 152 million kilometers (94 million miles) away from the Sun. That is approximately 5 million kilometers (3 million miles) further than during the perihelion in early January. That means the planet will move more slowly along its orbital path than at any other time of the year. As a result, summer is elongated by a few days in the northern hemisphere.
The word, aphelion, is Greek for “away from the sun”.
Earth is farthest from the Sun during summer in the northern hemisphere. Credit: TimeandDate.com