Retrograde planetary perihelion precession refers to the phenomenon where the perihelion, or the closest point of an orbiting body to the Sun, shifts direction during its orbit. Typically, perihelion precession occurs in a prograde motion, aligning with the orbit's direction. However, in retrograde perihelion precession, the perihelion moves opposite to the orbit's direction. This concept highlights the complexities of orbital mechanics and gravitational influences. Understanding these motions is essential for comprehending planetary dynamics.
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magheera
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I know what each word mean independently, I'm just confused as to what sort of motion is trying to be described as a whole.
Is a homemade radio telescope realistic?
There seems to be a confluence of multiple technologies that makes the situation better than when I was a wee lad: software-defined radio (SDR), the easy availability of satellite dishes, surveillance drives, and fast CPUs.
Let's take a step back - it is trivial to see the sun in radio. An old analog TV, a set of "rabbit ears" antenna, and you're good to go. Point the antenna at the sun (i.e. the ears are perpendicular to it) and there is...
3I/ATLAS, also known as C/2025 N1 (ATLAS) and formerly designated as A11pl3Z, is an iinterstellar comet. It was discovered by the Asteroid Terrestrial-impact Last Alert System (ATLAS) station at Río Hurtado, Chile on 1 July 2025.
Note: it was mentioned (as A11pl3Z) by DaveE in a new member's introductory thread.
https://www.physicsforums.com/threads/brian-cox-lead-me-here.1081670/post-7274146
https://earthsky.org/space/new-interstellar-object-candidate-heading-toward-the-sun-a11pl3z/
One...
Partial solar eclipse from Twizel, South Isl., New Zealand ...
almost missed it due to cloud, didnt see max at 0710 NZST as it went back into cloud.
20250922, 0701NZST
Canon 6D II 70-200mm @200mm,
F4, 100th sec, 1600ISO
Makeshift solar filter made out of solar eclipse sunglasses