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HIPASS galaxy catalogue (HICAT) animations


A series of animations constructed from the HIPASS galaxy catalogue (HICAT) and its northern extension to declination +25° (NHICAT) depicts the three-dimensional distribution of galaxies in the nearby universe (z < 0.03) as seen by a hypothetical observer who travels geometrically through them.


One frame of the 720 in nhicat-DVD-111a.flc shown at 85% actual size. True 3-D structure only becomes evident upon animation although clustering is clearly discernible in this 2-D view.


The celestial sphere is shown in a zenithal perspective projection at unit radius corresponding to a recession velocity of 3000 km/s (z = 0.01, 40 Mpc, 140 Mly). A little over half the catalogue lies within this sphere, thereafter the density falls rapidly to about 12000 km/s (z = 0.04, 170 Mpc, 540 Mly).

Galaxies are represented by coloured spheres with volume proportional to M(HI), the neutral hydrogen mass. To enhance the perspective effect, the marker size is corrected for its distance from the observer with appropriate object occlusion.

Marker hue represents recession velocity starting at blue for 0 km/s and cycling through cyan, green, yellow, and orange to red at the surface of the celestial sphere (3000 km/s) and beyond:
Colour km/s z Mpc Mly
blue 0 0.0000 0 0
cyan 750 0.0025 10 35
green 1500 0.0050 20 70
yellow 2250 0.0075 30 105
red ≥3000 0.0100 40 140
This provides an additional visual cue for identifying the members of particular structures. The table uses Hubble constant H0 = 72 km/s/Mpc:

The Milky Way at the centre of the celestial sphere is located by a fiducial marker with arms that point to the celestial poles and ra = 0, 6, 12, and 18h on the celestial equator; that which points to 0h is coloured yellow.

The celestial sphere is inscribed with a 15° equatorial graticule in grey, with IAU constellation boundaries in magenta labelled with their standard three-letter abbreviation. These are useful for orientation and identification of particular structures, particularly when aligned with the fiducial marker. Constellations associated with particular clusters or superclusters are marked in maroon. These are Virgo (Vir), Hydra (Hya), Centaurus (Cen), Fornax (For), Eridanus (Eri), Pavo (Pav), and Indus (Ind).

The supergalactic equator is marked on the celestial sphere in yellow with the galactic equator in green. The observer is in the equatorial plane of one of these systems when its equator is projected as a straight line intersecting the central marker. HICAT looks straight through the galactic plane which is not an obstacle for HI observations of distant galaxies.

The observer traverses a path that describes one or more figures-of-eight when projected onto the celestial sphere (marked in dark blue). In 3-D this motion is composed of three independent cycles:


  • Rotation of the celestial sphere on its polar axis.
  • The observer's orbit in a fixed plane containing the polar axis.
  • The distance of the observer from the centre of the celestial sphere. Depending on the animation, this varies between 0.05 and 5.0 radii as recorded in the table below.
The three digits in the name of each animation indicate the number of these cycles completed in the course of the animation.

In the "a", "i" and "o" animations the observer's trajectory is circular, whereas in the "s" animations the observer spirals in very close to the centre then out again.

The "i" (inner) animations show the region close to the Milky Way, while the "o" (outer) animations skim past the surface of the celestial sphere (at 3000 km/s, z = 0.01) mainly showing its contents. In these animations the observer moves gradually allowing plenty of time to appreciate the 3-D structure.

On the other hand, the "a" and "s" (spiral) animations cover a wide range of distances and angles in order to depict both the near- and far-field galaxy distribution. Consequently, the motion in these animations is much more dynamic, particularly in the latter, and they may seem like a roller-coaster ride in parts!

Stereoscopy is an obvious extension for representing 3-D structure. This is provided here in two ways; by stereo pairs, which require stereo projection equipment; and a red/cyan anaglyph which requires anaglyphic glasses (red on the left). In each the depth has been set so that the Milky Way at the centre of the celestial sphere is in the focal plane whence galaxies in the foreground appear to fly out of the screen. In earlier animations (produced several years ago) the stereo calculation was based on a simple rotation, the so-called "toe-in" method, which introduces vertical parallax and is not strictly correct. This has now been fixed by using a proper "off-axis" calculation.

The 3-D representation is generated by applying a parallax transformation to the galaxy distribution as seen from Earth to simulate what the observer would see in the night sky. That is, the distance and direction to each galaxy as seen from Earth is transformed to the distance and direction as seen by the observer. The distribution on the observer's celestial sphere is then projected onto the map plane using a gnomonic projection; it can be shown that this sequence of operations is equivalent to computing a zenithal perspective projection of the Earth-bound galaxy distribution with the observer at the point of projection.

However, the question naturally arises of using something other than the gnomonic projection to map the observer's sky. In particular, the choice of a cylindrical projection would allow the whole sky to be mapped, including the galaxies behind the observer. This is done, mainly out of mathematical interest, in nhicat-XGA-111C using Gall's stereographic projection - which is unrelated to stereoscopy!


Animations currently available:
Name R Max R Min Stereo view Resolution Frames Duration (mm:ss) FLC size (MiB) bzip2 size (MiB) No. files
nhicat-DVD-111a (sampler) 3.0 0.5 mono 720 x 576
5:4 ratio
720 0:29 108 35 4
nhicat-XGA-140i 0.5 0.5 mono 1024 x 768
4:3 ratio
2880 1:55 690 217 22
nhicat-XGA-141o 1.2 0.9 mono 2880 1:55 814 266 27
nhicat-XGA-410i 0.5 0.5 mono 2880 1:55 715 210 21
nhicat-XGA-411o 1.2 0.9 mono 2880 1:55 835 262 27
nhicat-XGA-165s 4.0 0.05 mono 4320 2:53 881 283 29
nhicat-XGA-475a 4.0 0.5 mono 5040 3:22 844 278 28
nhicat-XGA-475s-l nhicat-XGA-475s-r (stereo pairs) 4.0 0.05 left /
5040 3:22 1088 345 35
nhicat-XGA-111A (anaglyph) 1.1 0.5 red/cyan anaglyph 720 0:29 225 75 8
nhicat-XGA-411A (anaglyph) 1.2 0.9 red/cyan anaglyph 2880 1:55 965 326 33
nhicat-XGA-111C (cylindrical proj.) 3.0 0.5 mono 720 0:29 83 27 3
nhicat-SXGA-475s (large format) 5.0 0.05 mono 1280 x 1024
5:4 ratio
5040 3:22 1352 420 43


Notes on each animation


A number of structures are common to all of the animations:

  • The supergalactic plane, seen to good effect when the supergalactic equator is projected as a straight line through the central marker.
  • The local supercluster which fills most of the sphere to 3000 km/s; it has a characteristic arrow-head shape with the Virgo cluster at its tip when seen from locations in the supergalactic plane at northerly declinations.
  • The Virgo cluster, in cyan and green, at 1200 km/s (z = 0.004, 16 Mpc, 50 Mly).
  • The Fornax-Eridanus cluster, mostly in green at about 1500 km/s (z = 0.005, 20 Mpc, 65 Mly).


  • Pavo-Indus supercluster in red at about 4500 km/s (z = 0.015, 60 Mpc, 200 Mly).
  • Hydra-Centaurus supercluster in red at about 6000 km/s (z = 0.02, 80 Mpc, 280 Mly).
  • The Centaurus wall which appears to connect Centaurus to Indus through Norma.
  • The "Big Y" - a structure composed of three filaments stretching between about 1000 and 2500 km/s in the void towards Ophiuchus/Aquila easily seen in many of the animations.
  • Local Group and other nearby galaxy groups, in blue close to the Milky Way. Many low HI-mass galaxies can be seen in this region.

  • nhicat-DVD-111a A relatively small sampler that covers a range of distances providing a view of larger and smaller scales. Larger scale sheets (red) are seen edge-on in frames 100-170, the Virgo cluster (green) is visible behind the Milky Way in frames 380-390, and the supergalactic plane (blue-cyan-green-yellow) is edge-on at around frame 400.

  • nhicat-XGA-140i The observer travels at a fixed distance of 0.5 radii from the centre moving smoothly, mainly in declination. The observer's relatively close proximity to the Milky Way allows the sky to be seen approximately as from Earth. Virgo (green) is visible behind the Milky Way in frames 1-50, and Fornax-Eridanus (green) in frames 410-470. The "Big Y" is behind the Milky Way in frames 730-760.

  • nhicat-XGA-141o The observer travels close to the surface of the celestial sphere moving smoothly, mainly in declination, providing a clear view of the structure out to about 30 Mpc. In frames 2180-2300 isolated filaments (green-yellow) can be seen running through the void. These form the characteristic "Big Y" structure when seen face-on in many of the animations.

  • nhicat-XGA-410i Akin to nhicat-XGA-140i except that now the observer travels mainly in right ascension. Frames 1-1000 show the local neighbourhood out to Virgo particularly well, including the Southern Local Supervoid. In frames 1160-1250 the observer flies through Fornax (cyan/green) looking back on the Milky Way and then likewise through Virgo (green) in frames 1400-1500. The Hydra-Centaurus supercluster is visible in the distance (red) behind the Milky Way in frames 1800-1880. Shortly afterwards, Pavo-Indus (red) is seen in frames 1970-2000 slightly above centre.

  • nhicat-XGA-411o Akin to nhicat-XGA-141o except that now the observer travels mainly in right ascension. The Milky Way is seen through the Virgo cluster between frames 1450-1470. Between frames 280 and 460 the observer flies through the near side of the Hydra-Centaurus supercluster.

  • nhicat-XGA-165s Faster-paced than the previous animations, and travelling mainly in declination and over a wider range of radial distances. Starting from 12000 km/s (z = 0.04, 170 Mpc, 550 Mly) large-scale structure (red) is evident in frame 200 with Pavo-Indus (red) seen edge-on below and right of centre and Hydra-Centaurus (red) above centre. The observer skims past the latter in frames 250-300, and then Virgo (green) in frames 350-400 heading precipitately towards the Milky Way but then pulling out. A sheet formed by Hydra-Centaurus and Pavo-Indus is seen edge-on briefly in frames 950-960 and thereafter the "Big Y" (green-yellow) is prominent in frames 970-1030, the observer grazes past the end of its yellow arm in frames 1110-1130. The supergalactic plane is edge-on in frame 1660 towards the lower left, with the Southern Local Supervoid towards the upper left. The Sculptor Group (blue) is behind the Milky Way in frame 2100, and the local neighbourhood (blue) is seen well against the vacant northern hemishpere in frames 2200-2400. Thereafter the "arrow-head" converging on Virgo unfolds between frames 2500 and 2680. The observer is in the intersection of the galactic and supergalactic planes at frame 2638, and flys through Pavo-Indus in frames 3690-3750.

  • nhicat-XGA-475a Similar to nhicat-XGA-165s but travelling much faster in right ascension, though without spiralling towards the centre.

  • nhicat-XGA-475s This stereo pair is similar to nhicat-XGA-165s but moves at a faster pace in right ascension - a long roller-coaster ride provided mainly for the stereo projector system at the visitor's centre of the Parkes radio telescope. The supergalactic plane is seen nicely edge-on in frames 2750-2770, with Virgo (green) at lower left, Hydra-Centaurus (red) in the background just left of centre, and Pavo-Indus (red) just to its right.

  • nhicat-XGA-111A This red-cyan anaglyph, although lacking the colour-cues of the other animations, when combined with the observer's motion produces a powerful 3-D effect that is particularly effective in showing the voids. The stereo parallax geometry, as for nhicat-XGA-475s, has the focal plane positioned on the Milky Way at the centre of the celestial sphere, and an ocular separation of 0.01 radii (30 km/s).

  • nhicat-XGA-411A A red-cyan anaglyph version of nhicat-XGA-411o.

  • nhicat-XGA-111C This animation is for connoisseurs of spherical map projections! As explained above, the 3-D representation is generated by applying a parallax transformation to the galaxy distribution as seen from Earth to simulate what the observer would see in the night sky. This may then be mapped using any spherical projection; Gall's projection, used here, allows the whole sky to be seen with reduced distortion at mid-latitudes.

  • nhicat-SXGA-475s Very similar to nhicat-XGA-475s except in mono and in a larger image format that fills the screen of most desktop monitors and projector systems. The slightly greater maximum radial distance (15000 km/s, z = 0.05) allows the full radial extent of the HIPASS galaxy catalogue to be seen in the opening frames. (Motion artifacts at the right edge of some frames are apparently due to a bug in the graphics software.)



The animations have been produced in FLC format with reverse play capability when using the xanim player on unix/X11 systems. This player also allows on-the-fly speed adjustment and frame-by-frame stepping in each direction which is very useful for investigating 3-D structure. Suitable players are said to be available for Macs and Windows.

Some animations have both left and right stereo pairs, but if you do not have a stereo viewer there is little point in getting both views. Because of their size they have been bzip2'd and then split into 10 MiB files for download.

Firstly download the split files. You might find wget useful for this but recursive fetches are disallowed


by our robots.txt so follow the instructions in the links given in the table.

When playing the animations, particularly the larger ones, using xanim on my Dell Latitude D600 laptop (512 MiB, Debian sarge) I find that it is much better not to buffer them to memory; the i/o rate from harddisk (i.e. not network mounted) is more than adequate. (The i/o rate for the 60 GiB Fujitsu MHT2060AT internal disk, as measured by hdparm -tT /dev/hda, was 24 MiB/s with DMA enabled, though it was too slow without DMA.)

Thus use

  xanim +f nhicat-DVD-111a.flc
This should start playing in under 5 seconds, while nhicat-XGA-475a takes about 30 seconds to begin.


Converting to other animation formats


The venerable FLC format was found to be the most suitable for these computer animations. While MPEG provides better compression it does so at the expense of image quality, particularly in losing the fine grid lines. Although MPEG image quality may be improved by increasing the bit-rate, the MPEG file size then becomes comparable to the bzip'd FLC files without achieving the same quality.

Since FLC animations use lossless compression they may be decomposed into individual frames for conversion to other formats. The unflick utility undoes the operation of ppm2fli which was used to create them. (However, to support more than 4000 frames for the larger animations you will need to increase FLI_MAXFRAMES in upro.h and apro.h before compiling.)

Version 2.1 of unflick supports output filtering so, for example, to extract the frames as GIFs rather than the default


PPM, you could use

  unflick -f"ppmtogif -sort" -v \
    animation.flc animation- gif
which uses the netpbm filter, ppmtogif.

Once you have the separate frames you can recompose the animation in another format. The 720 x 576 image size was chosen to match that of PAL DVD which is based on MPEG2.

For example, a unix shell script was used to produce the 8 Mib/s MPEG-1 video nhicat-DVD-111a.mpg using the netpbm utility, ppmtompeg. However, although much more compact, image quality is notably inferior to FLC.

MPEG-2 and MPEG-4 video can be produced with mplayer/mencoder, unix shell scripts flctompeg2 and flctompeg4 may be used for this. However, the resulting MPEG-2 and MPEG-4 videos at the same bit rate (8 Mib/s) as the MPEG-1 video are virtually indistinguishable from it.


Dr. Mark R. Calabretta ( mcalabre@atnf.csiro.au)
Last modified: 2006/06/14