[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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More from @AstroKatie

2 Oct
Hello I am an astronomer, I have a small telescope and I’ve done lots of stargazing. I’ve never seen Mercury (it’s very close to the Sun) and I never pay attention to where it is in its orbit. The only impact it has on my life is unfortunate people blaming it for their troubles.
The thing people call “Mercury retrograde” is an accident of perspective by which if you WERE observing Mercury every night, sometimes it would appear a little east of where it was yesterday & sometimes a little west, from our perspective. But it’s just orbiting; nothing changes.
Unless you’re out there with a telescope and a sextant making charts of the position of a small dot near the Sun, you won’t observe apparent retrograde motion. Even if you were ON MERCURY you wouldn’t notice anything unless you were tracking Earth. It’s just not really a thing.
Read 5 tweets
10 Sep
I’m totally fine and there is no need to worry or anything like that (honestly!!) but I will not be answering e-mails today Me sitting in a hospital bed in a hospital gown, wearing an
Anyway if I tweet weird later, it’s just the anesthesia 😅
Thanks everyone for the well wishes! Surgery and post-op went fine and I’m home now and resting, looked after by @cavaticat. Still not answering any e-nails today 🙅‍♀️ Me peeking my face out of a giant mass of white blankets in Me reclining on a sofa at home looking woozy but smiling, we
Read 5 tweets
27 Aug
The seating chart makes it especially clear that defining a “close contact” as “within six feet for more than 15 minutes” is absurdly insufficient in the context of (1) an indoor space and (2) the Delta variant. Being close is worse but indoors the whole room is at risk.
The above kind of story is why I cringe every time I see a press conference or other event in which everyone is masked EXCEPT the speaker at the front. You create the most droplets and aerosols when you’re speaking — that’s when you need the mask MOST!
The official advice is “masks work best when everyone is wearing them.” They can be helpful protection for uninflected people to wear but they’re MOST helpful as source control: worn by infected people. With Delta, most transmissions happen BEFORE SYMPTOMS APPEAR. Please mask up.
Read 4 tweets
19 Aug
“74% of infections with Delta took place during the presymptomatic phase — a higher proportion than for previous variants”

Get vaccinated, get tested. You don’t know whether or not you’re contagious, and no one around you knows either.
Rapid testing can be a very useful tool to help reduce spread. Rapid tests like these (about $20 for two tests) aren’t perfect & can give false negatives BUT if used widely & often they can catch infections before symptoms show up. (Some govts subsidize them; the US should too.) Three boxes of the “BinaxNOW” brand Covid-19 antigen sel
<looks meaningfully in the direction of the US government>
Read 4 tweets
14 Aug
Thanks everyone for your questions! I have stopped answering now but check out the tweets below to see if any of your own questions have been asked by someone else and answered here! I'll quote tweet a few.
Read 11 tweets
10 Aug
TBH I would rather risk hurting someone’s feelings by changing my behavior in response to a choice they have made than risk inadvertently passing a potentially deadly virus on to anyone I might come in contact with
Isolation from your friends is terrible but an isolation ward in a hospital is worse
So anyway yes I will be rude to you if that rudeness might down the road save the life of a stranger; I wish you a speedy and painless recovery from the slight
Read 4 tweets

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