[poll] Did you know? #MercuryRetrograde is when Mercury:
For a really great explainer of what #MercuryRetrograde actually means, check out this video by @JossFong vox.com/2016/9/10/1286…
The short version is that because Mercury is closer to the Sun, it orbits faster than us, and so if we were to chart its sky position relative to distant stars, when it’s scooting between us and the Sun it’ll look like it’s going the “wrong” way. But it’s a trick of perspective.
You can play around with this website theplanetstoday.com to see the positions of the planets now and on different days. The site helpfully highlights when retrograde occurs! But also correctly points out that, being an illusion, it has no real significance to astronomers. 🙃
Apparent retrograde motion had a BIG significance to astronomers when it was first discovered (for Mars, not Mercury; Mercury’s always been a bit tricky to observe), because it helped to prove that the planets all revolve around the Sun — not us.
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