Besides being Independence Day, Monday is also aphelion day when Earth is farthest from the sun at 94.5 million miles.
There is a slight flexure in the Earth’s orbit from the gravitational interaction with the moon and, by a smaller amount, the planets, so the precise aphelion value changes. Tomorrow it will be 94,509,598 miles but next year it will be slightly less at 94,506,364 miles and in 2024, it will be 94,510,539 miles.
The fact that aphelion occurs during our summer shows that the distance from the sun is not the reason for the seasons. The steeper angle of the sunlight striking our part of the Earth in the summer concentrates the sun’s energy and the longer time the sun is above the horizon during the summer, means it will be warmer in the summer than the winter (greater baking power and baking time means it bakes in the Bakersfield summer).
In June, early morning risers had a great view of all of the naked-eye planets in the eastern sky. On June 24, the lineup including the crescent moon had all of the objects beautifully displayed in the same order as their distance from the sun and all roughly equally spaced.
Monday morning or the morning after will probably be the last time to see all of the planets at the same time. They are still displayed in the same order as their distance from the sun. Mercury is dropping quickly back toward the sun, so it will be soon lost in the twilight glow.
The separation between the two ends, Mercury and Saturn has increased to the point where they won’t fit on the same star chart. The accompanying chart focuses on the more easily visible planets: Venus, Mars, Jupiter and Saturn. The moon is in the evening sky as a waxing crescent in the west. It will be at first quarter (half lit up) on Wednesday night and at full phase on the night of July 13.
Setback for Psyche
In space exploration news, there was a setback for the Psyche mission that will explore the metallic asteroid of the same name. A delay in getting the spacecraft’s flight software pushed back the testing of the systems to beyond the launch window that runs from Aug. 1 to Oct. 11. That launch window would have had Psyche using a gravitational assist from Mars to boost the spacecraft to arrive at the asteroid in 2026. The launch windows in 2023 and 2024 will be paths that do not include a Mars boost, so Psyche won’t arrive until 2029 or 2030.
The asteroid Psyche is about 130 miles across and resides in the asteroid belt about three times farther out from the sun than Earth. What is so unusual about Psyche is that it is composed mostly of metallic iron and nickel, like our planet’s core. Other asteroids are mostly rocky or icy bodies. Psyche might be an exposed core from an early planetesimal that lost its outer rocky mantle and crust from the numerous violent collisions that pounded all solid objects in the early solar system. Beyond its scientific value, a metal world might be an attractive source of materials.
On a positive note, the James Webb Space Telescope is scheduled to release its first images and spectroscopy data on July 12 at 7:30 a.m. Pacific Daylight Time. There will be a live press conference with simultaneous release on the major social media platforms and on the website nasa.gov/webbfirstimages.
On July 13 at noon, Webb experts will answer questions about the first images and data in a NASA Science Live show on YouTube and Facebook. People can submit questions on Twitter using the hashtag #UnfoldtheUniverse or in the YouTube/Facebook chat sections.
Contributing columnist Nick Strobel is director of the William M. Thomas Planetarium at Bakersfield College and author of the award-winning website AstronomyNotes.com.