Pappus' plane

A collection of space gifs. Now only occasional updates.

[christinetheastrophysicist]

The Movement of Barnard’s Star 

The fourth closest known star to our Sun (following the Alpha Centauri stars), Barnard’s Star is famous for having the largest known proper motion of any star. Proper motion is the measure of the observed changes in a star’s position against the distant background stars and in 1916, E. E. Barnard measured this star’s proper motion to be 10.3 arcseconds per year. This corresponds to a speed of 90 km/s across our line of sight.

This movie by RickJ, posted in the CosmoQuest forums, shows the movement of Barnard’s Star over 9 years. Each frame represents one year between 2007 and 2015. 

Image: The proper motion of Barnard’s Star over the last 9 years. (Credit: RickJ)

[pappubahry]

Clouds on Saturn, photographed by Cassini, 3 April 2014.

[pappubahry]

Ringlets in the Encke Gap of Saturn's rings.  Photographed by Cassini, 14 December 2006.

Wait, 2006?  Why wasn't this gif posted a year or two ago?

In the olden days (before March 2014), Tumblr's animated gif limits were an utterly confusing nightmare.  Officially you were limited to 1MB filesize and some pixel limits, but there was obviously something more going on.  With one exception, gifs longer than 99 frames would (for me) fail to upload.  Sometimes I'd have to cut the frame number to below 50.  It was horribly inconsistent.

The gif in today's post is 154 frames long, and it, like so many other long gifs, failed to upload when I first made it.  Then a few weeks ago I stumbled across a post from the Tumblr Engineering blog, saying that they'd fixed the gif irregularities!  

The old problem had been caused by a couple of limits imposed by Tumblr: not only did the uploaded gif have to be below 1MB, but all resized gifs also had to be below 1MB.  Furthermore, the resizes had to take less than 20 seconds.

The linked blog post doesn't say if they used to use ImageMagick for these gif resizes, but it wouldn't surprise me.  It's what I use, and a) it can be very slow to convert long gifs, especially with the -layers Optimize option, and b) it does some very strange things to file sizes sometimes (e.g., making the file bigger when you shrink it)

Tumblr worked with Gifsicle to get a tool which was fast, gave good results on resizing, and didn't bizarrely increase file sizes.  And so today we belatedly see these Encke Gap ringlets in gif form.

(I don't have any other old long gifs waiting to be uploaded; all others I just truncated as much as necessary.)

[pappubahry]

A dark Saturn and rings, photographed by Cassini, 11 January 2014.

[pappubahry]

Wonderfully smooth wagon-wheel effect from Saturn's polar hexagon.  Photographed by Cassini, 22 March 2014.

[pappubahry]

Saturn's polar hexagon (some edges of which are just visible) and the vortex at the pole.  Photographed by Cassini, 31 March 2014.

Cassini's been orbiting a long way off the ring plane lately, which for the most part doesn't generate many gif-able sequences, but does give us lots of views of the hexagon.  I had originally planned to have new posts every fortnight or so (ha!); perhaps one a month from here on is more realistic.

[ageofdestruction]

close watch: Clouds and their shadows on Mars, photographed 5 times by Mars Express, 12th September 2010.

At 38°S, 27°E, on the northeast plains of Noachis Terra. This gif covers about one minute of real time. For scale, the larger crater is 35km across; I particularly like the little puffball of cloud that moves across it.

The contrast of landscape flickers slightly because the images are taken sequentially through different filters, intended to be combined into a single colour image.

Image credit: ESA. Animation: AgeOfDestruction.

[pappubahry]

Saturn, photographed by Cassini, 12 August 2013.

[pappubahry]

Another look at the polar vortex on Saturn (previously featured here), photographed by Cassini, 14 June 2013.

[pappubahry]

Saturn and some of its moons, photographed by Voyager 2, 1 September 1981.

After the Saturn flyby, Voyager 2's scan platform got stuck, which meant that it couldn't change where its camera was pointing.  As a result, it just sat there taking photos of Saturn for a while, some of which are seen in the gif above.  (Obviously the camera could move a little bit, as seen by the way the top of the picture moves.)

The story of Voyager 2's Saturn flyby is told in this (half-hour) contemporary documentary, which shows some of the daily press conferences, including early speculation about the physical processes behind what they were seeing in the pictures being sent back, and a demonstration of the scan platform.  It concludes by talking about the future for the Voyagers, saying that before its power runs out, Voyager 1 should reach the edge of the solar system.

A bit after the 3-minute mark, it also shows a video of spokes in Saturn's B Ring.  That very video (cropped, truncated, and processed a little) was the subject of my first Tumblr post.

And, having started with Voyager 2 at Saturn, I'll now end the daily updates of this blog with this gif from Voyager 2 leaving Saturn.  I might still update occasionally, especially since Cassini will continue to send photos back from Saturn for years, but I've mined the archives of the older spacecraft as much as I have the will to do so.

Thanks to the followers who've joined me along the way; I hope that these little time-lapse animations have increased your admiration for humanity's space programmes, as they certainly have for me.

The blog hasn't quite made it to 400 gifs (my original optimistic goal was 200!), but it got pretty close.  You can navigate through them by mission or object from the right-hand margin.

[pappubahry]

Io transiting Jupiter, photographed by Voyager 1, 31 January 1979.  South is up, which is why the Great Red Spot's in the upper hemisphere.

(As with yesterday's gif, I'm not fully certain I've identified the moon correctly: it looks like Io to me, and the orbital speed seems about right, but for the life of me I can't get HORIZONS to agree with the pictures: at the time of the first frame (C1541036), my spreadsheet tells me that none of the Galilean moons should even be in the frame.  The problem's fixed if I pretend that the z-coordinate of every position is zero, but that's cheating....)

[pappubahry]

Ganymede transiting Jupiter, photographed by Voyager 1, 31 January 1979.  South is up.

(I'm not completely sure that it's Ganymede: it looks like Ganymede to me, and estimating its orbital speed from the photos gives a decent match to the true value, but I've had issues getting moon positions to match the photos from Voyager 1's approach to Jupiter.)

[pappubahry]

Galileo, which spent the better part of a decade orbiting Jupiter, being launched from the Space Shuttle Atlantis during STS-34, 18 October 1989.

Galileo gifs have occasionally been featured on this Tumblr, though not as often as we'd like.  Its main antenna didn't unfurl properly, and with a much-reduced bandwidth, only a bare minimum of photos were sent back to Earth from Jupiter.  That bare minimum was still sufficient for pretty mosaics (e.g., Europa; Io), but not enough for the smooth time-lapse sequences that Cassini spoils us with.

[pappubahry]

Tall structures, presumably caused by moonlets, near the outer edge of Saturn's A Ring, photographed by Cassini, 26 July 2009.  (The photos in this sequence weren't taken frequently enough to actually follow the motion of individual peaks.)  More descriptions here; the tallest of the peaks is about 2.5km above the ring plane.

[pappubahry]

In orbit from the Space Shuttle Discovery during mission STS-31, 26 April 1990, starting near Mauritania and Western Sahara.  I believe the altitude here was around 600km (it was the mission which launched Hubble), about twice as high as the altitude from which we see most photos of Earth from space.  (Mission-roll-frame STS031-151-15ff.)

[pappubahry]

More of the Crab Pulsar sending waves into the surrounding nebula, photographed by the Hubble Space Telescope.  The first sequence is from December 1995 to February 1996 (Proposal ID 6129); the second is from February till March 2000 (Proposal ID 8552).  I earlier posted an eight-month long sequence of the same phenomenon.

I used raw exposures an did my best to get rid of the (substantial amount of) noise, with partial success; if I had my time over I'd have used the HLA's "Level 2" products.

[pappubahry]

The SBS-4 satellite being deployed from the Space Shuttle Discovery during mission STS-41-D, 30 August 1984.  (Mission-roll-frame STS41D-36-14ff.)