July 4
Aphelion Day
Sun Position
The Sun is in Cancer at approximately +22.9° declination. Northern midsummer; Southern Hemisphere midwinter. On this day Earth reaches aphelion (maximum distance from the Sun) making it the slowest point in Earth's annual orbit.
Sky Highlight
Earth reaches aphelion on approximately July 4 each year, sitting about 152.1 million km from the Sun. At this point Earth moves at its slowest orbital speed (roughly 29.3 km/s versus 30.3 km/s at perihelion), so Northern Hemisphere summer is actually the longer of the two seasons by a few days, the year's second half, from aphelion back to perihelion, takes slightly longer. No hemisphere asymmetry for aphelion itself.
Deep Sky Object
M13 (NGC 6205), the Great Hercules Cluster, a globular cluster roughly 22,000 light-years away in Hercules. It contains several hundred thousand stars and is one of the brightest globular clusters visible from the Northern Hemisphere; binoculars show a fuzzy patch, while a small telescope begins to resolve its edges. In 1974, the Arecibo message was broadcast toward M13.
Featured Star
Albireo (β Cyg) is a celebrated double star in Cygnus about 430 light-years away, consisting of an orange giant (K3II) and a blue main-sequence companion (B8Ve). The color contrast (amber and blue-white) is often cited as the most striking color pair visible in a small telescope, and the stars are probably gravitationally bound despite their wide apparent separation.
Around This Date
- July 4, 1054Chinese astronomers first recorded the supernova in Taurus that produced the Crab Nebula, noting it as a 'guest star' visible in full daylight for roughly three weeks.
- July 4, 1997NASA's Mars Pathfinder spacecraft landed on Mars, deploying the Sojourner rover, the first wheeled vehicle to operate on another planet.
On the day Earth drifts farthest from the Sun, the sky still puts on the same show, distance, it turns out, is less decisive than tilt.