#Tag · 𑐴𑐶𑐟𑐶

Phil Stooke @PhilStooke@mastodon.social · 5 months ago

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No - Schiaparelli saw Mars like this - with south at the top. Until the dawn of the space age most planetary maps were drawn with south at the top as seen in an inverting astronomical telescope. Only when maps might be used for direct physical exploration did the convention change to avoid potential confusion. Rather than turn our screens upside down, let's do a 'rotate 180 degrees' in Photoshop. Simples! #maps #Mars #Hubble

This is the previous Hubble Space Telescope image turned upside down to match the view from a astronomical telescope, which inverts the image.

Phil Stooke @PhilStooke@mastodon.social · 5 months ago

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We need a bit of a mind-flip to understand how Schiaparelli developed his naming scheme. We start with a map of Mars - let's use a modern one from the Hubble Space Telescope. But Schiaparelli didn't see Mars like this... #maps #Mars #Hubble

A map of Mars made by combining several images taken by the Hubble Space Telescope into a cylindrical projection. The poles are cloudy but the rest of the planet has its characteristic orange colour (iron oxides) with various darker markings.

Phil Stooke @PhilStooke@mastodon.social · 5 months ago

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Now we need to look back in time to the classical understanding of the world. How better to do that than with Ptolemy's map of the world known to him at the time? None of Ptolemy's maps survived into the medieval world, but his list of places - a sort of gazetteer - did. 8000 places with his estimates of their latitude and longitude, from which his maps have been reconstructed. See the similarity? No, nor do I, but Schiaparelli found a way to link them. #maps #Mars #Ptolemy

A map of the world (as know to him) by Claudius Ptolemaeus, or Ptolemy, c. the year 150. It didn't survive but has been reconstructed from lists of places and their latitude and longitude.

Phil Stooke @PhilStooke@mastodon.social · 5 months ago

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I answered my first map question in a separate post. Back to Herschel: his map has no coordinates but coordinates can be approximated. I projected the Herschel map into a cylindrical projection and then into two equator-centred azimuthal projections making the best match I could to modern coordinates. My intention was to take a variety of historical and recent maps in different projections and display them all in a common format for comparison. #maps #Mars #Herschel

William Herschel's map of Mars reprojected into an equator-centred pair of azimuthal projections, roughly matched to modern coordinates.

Phil Stooke @PhilStooke@mastodon.social · 5 months ago

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Here is Herschel's actual map (left). I compare it with a mid-20th Century map in the same projection (azimuthal, extending from the south pole at centre to the mid-latitudes in the northern hemisphere). There's no coordinate grid but it vaguely resembles the more modern map. It's the first map of Mars, but not the first map of another planet. Anyone care to speculate who made the first map of another planet, and which one? #maps #Mars #Herschel

William Herschel's 1784 map of Mars (left) and a mid-20th Century map in the same (approximate) geometry (right). I will identify the more modern map when we get to it in the sequence.

Phil Stooke @PhilStooke@mastodon.social · 5 months ago

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The next stop on our history of Mars mapping is the German astronomers Beer and Mädler. Working in the 1830s and 40s, they took Mars maps a significant step further, establishing a coordinate system and a prime meridian which is essentially what we use today. Here is the map made from observations in 1830 (published 1831) when the southern hemisphere was visible (as for Herschel). The south pole in in the middle, 30 north at the outer edge. #maps #Mars #Beer #Mädler

A map of Mars made in 1830 by German astronomers Beer and Mädler. it shows the south pole at the centre and 30 degrees north at the outer edge in an interrupted azimuthal projection.

Phil Stooke @PhilStooke@mastodon.social · 5 months ago

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This map is what you get if you transform the Beer and Mädler map into the same projection I used for Herschel a few posts ago. Both polar azimuthal maps were transformed to cylindrical and combined to give global coverage (taking the opportunity to fix that pesky mistake), then transformed again to an equator-centred azimuthal equidistant projection. Now it gets a bit easier to compare with modern maps. #maps #Mars #Beer #Mädler

The Beer and Mädler map of the previous post is shown here in another azimuthal projection, this time centred on the equator in two hemispheres.

Phil Stooke @PhilStooke@mastodon.social · 5 months ago

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In 1841 Beer and Mädler published a map of the whole planet after the north pole became visible later in the 1830s (it all depends which pole is tilted towards us when Mars is closest to Earth). They stuck with polar projections which led them into a clumsy mistake. I'm just glad I'm not the only one - you can't be out there as much as I am without making public mistakes. Look at the longitude of feature 'f' (= Syrtis Major) in the two hemispheres. One (north) is wrong. #maps #Mars #Beer #Mädler

Mars mapped by Beer and Mädler in 1841. The whole planet is shown in two pole-centred hemispheres. Splitting the map at the equator caused a mistake. A feature labelled 'f' (it is what we would call Syrtis Major) is at about longitude 70, but in their northern hemisphere it is at about 100 degrees. Mädler drew the map, and he must have kicked himself when he noticed.

Phil Stooke @PhilStooke@mastodon.social · 5 months ago

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Do these features match things we see today? (a faithful reader asks). Yes, and here are a few names - the traditional telescopic feature names like Meridiani Sinus (Sinus = Bay), not the modern topographic names like Meridiani Planum (Planum = plateau), though they are obviously related. And Meridiani refers to the dark spot Beer and Mädler chose to mark the prime meridian.

These maps are from my first Mars atlas. I won't show every historic Mars map, just a few interesting ones. #maps #mars

This is the map in the previous post with some feature names added to help orient yourself.

Phil Stooke @PhilStooke@mastodon.social · 5 months ago

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Here is a modern (i.e. Cassini) map of Rhea with feature names:

https://asc-planetarynames-data.s3.us-west-2.amazonaws.com/rhea_comp.pdf

If you want to explore all such solar system names, go here:

https://planetarynames.wr.usgs.gov/

Use the menu bar underneath the banner image to explore names on maps of many worlds. You will notice asteroids are included. But interestingly, for some reason, not comets. I don't know why not. Even Rosetta's amazing comet 67P, which did get names in publications, never got official status for them. #maps #planets