July 3
The Retired Pole Star
Sun Position
The Sun is in Cancer at roughly +23° declination. Northern midsummer holds; Southern Hemisphere nights are long and cold, excellent for observing circumpolar objects from southern latitudes.
Sky Highlight
Earth reaches aphelion around July 4, its farthest point from the Sun each year. On July 3 the planet is within a day of that maximum distance. The roughly 3.3% difference between aphelion and perihelion distances has essentially no effect on seasonal temperatures, which are governed by axial tilt, not distance.
Deep Sky Object
NGC 6543, the Cat's Eye Nebula, a planetary nebula in Draco roughly 3,000 light-years away. It has a complex, concentric shell structure that Hubble imaging has made iconic, likely produced by a binary central star shedding layers at irregular intervals. Circumpolar from most of the Northern Hemisphere and well-placed on July evenings.
Featured Star
Kochab (β UMi) is an orange giant about 130.9 light-years away in Ursa Minor, classified K4III. Due to Earth's axial precession, Kochab served as the north pole star for several thousand years centered around 1500 BCE (Homer's sailors would have steered by it) before the celestial pole drifted away toward Polaris.
Around This Date
- July 3, 1969The Soviet N1 moon rocket, designed to carry cosmonauts to the Moon, exploded 10 seconds after launch at Baikonur, the largest non-nuclear explosion in history at the time, destroying the launch pad.
- July 5, 1687Isaac Newton's Principia Mathematica was published, providing the mathematical framework for universal gravitation that allowed future astronomers to predict the positions of every body in the solar system.
Kochab has not moved, but the Earth has tilted away from it, a quiet reminder that even the fixed stars are only fixed for a while.