I couldn't help it and had a go at that awesome MeerKAT image of the Milky Way centre recently released by @SKA_Africa Rather than just plotting the intensity, I've used a colour palette to map the spectral index. 🌈 For those who wanted a high-resolution version and/or a colourbar mapping the spectral index, I've uploaded it to Flickr:

flickr.com/photos/astro_j…

Just click on the download button to the lower right and pick whatever resolution you prefer, up to 7.5k by 4.7k pixels.

1/ Today’s APOD is this beautiful shot by Gerardo Ferrarino (g.ferra on Instagram), featuring the Andromeda galaxy, the closest spiral galaxy. You may have read tweets saying this is how Andromeda would look like if it was brighter, but that’s not quite true. Thread! 2/ Andromeda spans 3 degrees on the sky. How much is that? Well, one finger at arm’s length is about 1 degree wide. So if you extend your arm you would be able to cover the entire galaxy with 3 fingers. That’s big, but not *that* big!

1/ I took this picture of @ESO’s UT4 telescope back in January. You may have read that we use lasers to correct atmospheric turbulence, but how does this work exactly? And why do we need several lasers rather than just one? Thread! 2/ Ground-based observations are affected by atmospheric turbulence, which blurs the images of astronomical sources. But we can use high speed deformable mirrors to counteract this turbulence and get very sharp images, as I explained here:

https://twitter.com/astro_jcm/status/1229398249699774465

1/ I have the feeling that all those Musk followers who want to move to Mars have extremely romanticised and unrealistic expectations of what it's like to live in another planet. Since I (kind of) live of Mars, let me tell you my own experience...

https://twitter.com/AstroKatie/status/1223265967196819459

2/ The Atacama desert looks a lot like Mars, to the point that our colleagues from the European Space Agency often come here to test Mars rovers:
eso.org/public/announc…

1/ Every once in a while clouds pay us an unwelcome visit at Paranal. This can ruin our observations, but on the other hand we can enjoy amazing Moon halos like this one I saw in November. Do you want to learn how these haloes form? Thread! 2/ These haloes are created by hexagonal ice crystals in the atmosphere. Incident light rays are refracted twice as they go through two faces of the crystals at 60º with each other. The beam then emerges at a certain deviation angle relative to the incident beam.

What I love about this chart is that back in the XIX century we actually thought that there was indeed a mysterious planet inside Mercury's orbit. We even gave it a name: Vulcan.

https://twitter.com/xkcdComic/status/1220063691317510144

As you know, planets follow elliptical orbits around the Sun. But Mercury's orbit is weird, as the ellipse itself rotates. This is called "precession", and other bodies do that too. Except the precession of Mercury's orbit can't be explained with Newton's laws.

1/ This is a wide-field picture of Orion I took last night with a diffraction grating in front of my camera lens. It's a great way to visually compare the spectra of different astronomical sources. Let me explain what we're seeing here, because there's a lot to unpack here... A diffraction grating is a piece of glass, plastic or a similar transparent material with lots of lines engraved on it, very close to each other. When light goes through a diffraction grating it gets decomposed into its constituent colors.

Image credit: opentextbc.ca/universityphys…

I'm reading some comments saying that, as Starlink satellites are getting fainter to the naked eye, astronomers should stop complaining. Apart from the fact that they still flare, here's a short thread explaining why even faint satellites are an issue for us. 1/ Under dark conditions your pupil is, at most, 8 mm wide. Telescopes like VLT, Keck, Subaru, GTC or LSST are 8-10 m wide. The light collecting area goes as the diameter squared, so these telescopes collect 1 million times more light than your pupil in the same amount of time.