"Dog Days" of Summer Begin Today, July 3, Through August 11

The “Dog Days” of Summer officially start today, Thursday, July 3. Most people casually refer to the "Dog Days" as a period of hot and humid weather. But did you know that the dog days are a 40-day period which lasts from early July through mid-August?

The dog days of Summer run from July 3 through August 11 in the Northern Hemisphere and have to do with the star Sirius, known as “the dog star.” Sirius is the brightest star in the Northern Hemisphere other than the Sun, and it is found in the constellation Canis Major; thus the name “dog star.”

In the Summer, Sirius rises and sets with the Sun. During late July, Sirius is in “conjunction” with the Sun. The ancients believed that its heat added to the heat of the Sun, creating a stretch of hot and sultry weather. They named this period of time, from 20 days before the conjunction to 20 days after, the “Dog Days” after the dog star.

In ancient times, when the night sky was unobscured by artificial lights and smog, different groups of peoples in different parts of the world drew images in the sky by “connecting the dots” of stars. The images drawn were dependent upon the culture.

The Chinese saw different images than the Native Americans, who saw different pictures than the Europeans. These star pictures are now called constellations, and the constellations that are now mapped out in the sky come from our European ancestors.

They saw images of bears (Ursa Major and Ursa Minor), twins (Gemini), a bull (Taurus), and others, including dogs (Canis Major and Canis Minor). The brightest of the stars in Canis Major (the big dog) is Sirius. The star can be seen prominently in the Winter in the Northern Hemisphere, adjacent to Orion the Hunter.

The conjunction of Sirius with the Sun varies somewhat with latitude. Also, the constellations today are not in exactly the same place in the sky as they were in ancient Rome. Although we are in the middle of the dog days of Summer right now, the heat is not due to the added radiation from a far-away star, regardless of its brightness. The heat of Summer is a direct result of the earth’s 23.5 degree tilt on its axis, meaning the Northern Hemisphere is tilted toward the Sun during the Summer.

Welcome to the "Dog Days."

Paul

Earth at Farthest Point from the Sun During Its Annual Elliptical Orbit

Despite the hot weather this week, our planet is actually at its farthest point from the Sun today. According to the U. S. Naval Observatory, the Earth reaches a point in its orbit called "aphelion" at 3:54 p.m. EDT. The Earth's aphelion is the point where it is the farthest from the Sun than at any time during the year at a distance of 94,510,539 miles.

The Earth is typically about 93 million miles from the Sun. However, because our planet's orbit is not a perfect circle but an ellipse, it has a farthest point and a closest point to the Sun. In case you're wondering, the Earth's closest approach to the Sun is called perihelion, and that occurs in early January. The Earth is exactly 3,104,641 miles (or 3.28 percent) farther from the Sun than at its closest approach. The Earth actually receives about seven percent less heat at its aphelion than at its perihelion, according to researchers.

Although the date for both will vary from year to year, the Earth will always be closest to the Sun in early January and the farthest away in early July. Not surprisingly, that comes as a shock to most people. At perihelion, our planet is about 91 million miles from the Sun. It moves outward to about 95 million miles from the Sun at aphelion. Naturally, some people have the mistaken impression that our seasons are caused by the changes in Earth's distance from the Sun, but this is not the case.

The temperatures and the seasons are not affected by the proximity of the Earth to the Sun or even the rotation of the planet on its axis. Rather, it is the tilt of the Earth that determines the climate. When it is at perihelion in January, the Northern Hemisphere is tilted away from the Sun, However, when it is at aphelion in July, the Northern Hemisphere is tilted toward the Sun.

Happy Aphelion Day.

Paul