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Introduction to SalsaJ
Powers of 10
This exercise has benefited from the help of Thomas Boudier for the biological images and Nicolas
Rambaux for the Solar System images.
 Open SalsaJ 2.0. Once the software is opened, the SalsaJ toolbar appears:

Scaling in biology:
1. Open the image images_power10/biology/mouse.jpg with File/open or “Open Image File”
2. When you move the (computer) mouse on the image the X,Y positions (in pixel units) are
displayed in the bottom left corner of the SalsaJ toolbar. This enables you to perform
position measurements on the image.
3. Click on the « straight line selection » icon
, then draw a line between the two eyes, the
angle and length appear next to the pixel position The “Plot Profile” tool
grey intensity along this line.
, displays the
4. Derive the corresponding length in pixels.
5. We know that the spacing between the two eyes is 1cm. Calculate the scale of the image in
mm/pixel, then set it with Analyse/Set Scale. Then the X,Y positions which appear in the
bottom left corner of SalsaJ toolbar are in the unit system you provide, instead of pixels.
6. Draw a scaling bar of 1cm with Analyse/Scale Bar.
This project has been funded with support from the European Commission.
This publication [communication] reflects the views only of the author,
and the Commission cannot be held responsible for any use which may be made of the information contained therein.
7. Estimate the size of the head and of the ears.
8. This image is a colour image, a so-called RGB image. Hence, next to the position (X,Y),
which appears at the bottom left corner of the SalsaJ toolbar, are displayed 3 values of
intensity corresponding to the images associated respectively to the Red, Green and Blue
colours. Click on “Image/Color/RGB Split”: 3 grey images taken in different filters appear.
You can get the original RGB image with “Image/Color/RGB Merge”.
9. Open the image “images_power10/biology/neurone_rat.png”.
10. Estimate the size of the Soma of the rat neuron.

Scaling on the Moon:
1. Open2 the image “images_power10/Moon/orth90east400m_km.tif” with “File/open” or the
“Open Image File” icon. This is a single colour image: only one intensity value is displayed.
2. Use the “Magnifying glass”
to zoom in and out with the left and right button on the
mouse. Zoom in until you can see the individual pixels.
3. Use the “Scrolling Tool”
window.
to move around. It is also possible to manually enlarge the
4. The pixel size of this image is 400 m/pixel. Check with “Analyse/Set Scale” that this is
properly set.
5. Click on the button “Brightness & Contrast”
in the toolbar. A new window appears. On
the top, an histogram with the values of the pixels of the image is displayed. Here, we have
an 8bit image, so the pixel values are spread between 0 and 256 (in arbitrary units). It is
possible to adjust the minimum and maximum values displayed using the corresponding
sliders. Close the window “Brightness & Contrast”. Click on Image/Lookup Tables/Show
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This image is quite large, if there is an « out of memory » message, close SalsaJ, and re-open « SalsaJ for webcam »,
which allocates 256 Mbytes of memory.
LUT. A palette (the so-called LookUp Table) appears with the corresponding between the
colour coding and the intensity in pixel count. It is possible to change the colour coding of
the active image with “Image/LookUp Tables”.
6. In which direction is the Sun?
7. Identify what are the black and white features on the image.
8. Humboldt crater is located at the position x=1504km y=2518.4km. Find it and measure its
diameter in km. Calculate its surface in km2.
Image observed from space (LROC)
Mosaic of 3700 images
Image observed from Earth
9. Count the number of small craters (with a diameter larger than 1km and larger than 4km)
inside the Humboldt crater. This requires some method to store the measured diameters, e.g.
in an Excel or other spreadsheet (or simply note them down on paper).
Density (number of craters with a diameter larger
than 1km per km2) as a function of absolute age in
Gyr. Linda M. V. Martel 2010 (Hawaii Institute of
Geophysics and Planetology).
Density (number of craters with a diameter
larger than 4km per km2) as a function of
absolute age in Gyr (or billion year).
Horz et al. (1991).
10. Calculate the density of small crates inside the Humboldt crater and then use the above
figures to estimate the age of the Humboldt crater.
Artist view of Cassini orbiting around Saturn.
Trip of Cassini from Earth to Saturn, which lasted 17 years.

Scaling with Saturn, its rings and its satellites :
This application requires some critical thinking... What are you measuring? Does it make sense?
1. Open the image “images_power10/SaturnAndAround/Saturn_rings_HST.jpeg” using the
shortcut “File/open” or the “Open Image File” icon. This image has been taken in 1996 by
the Hubble Space Telescope (HST), orbiting the Earth.
2. Knowing that the spatial resolution of the HST is 0.1 arcsec (1 arcsec=1/3600 degree) and
the distance of Saturn from the Sun is 1,429,400,000 km (= 9.54 AU ) 3, can you measure
the thickness of the rings?
3. Now, open the four images :
images_power10/SaturnAndAround/Saturn_PIA12677.tif
Saturn_PIA08158.tif
Saturn_PIA08196.tif
Saturn_PIA12513.tif
by clicking on shift and the left button of the mouse. Use “Window/Tile” to organise them
on the desk.
4. Knowing the resolution at Saturn and the view point (distance from Saturn) given in the
table below, you should be able to give a new estimate for the thickness of the rings. What
can you conclude?
Image
Pixel size on Saturn
Saturn_PIA12677.tif
Saturn_PIA*****.tif
116km/pixel
17km/pixel
Saturn-Cassini
distance
2.0 106 km
2.9 106 km
5. The thickness of Saturn rings is difficult to measure: they are unresolved on all the
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1 Astronomical unit=1 AU=149.6 109m.
photographs and thought to be as thin as 10 m (even if, considering they are not perfectly
planar, their effective thickness could be between 200 m and 3 km).
6. Open the file “images_power10/SaturnAndAround/Saturn_rings_cassini.jpeg”.
7. Knowing the diameter of Saturn is 120,536 km, estimate the total extension of the rings.
8. Saturn has more than 50 named satellites. We provide images for some of them. The pixel
size (given below) is different for each image, as the observing spacecraft is at a different
distance from each satellite. Estimate the size in km of each satellite as well as its shape
(defined as the ratio of the X/Y axis size). How do these two properties relate?
Image
Pixel size
Lapetus.tif
Hyperion.tif
Helene.tif
Enceladus.tif
Dione.tif
Pandora.tif
Epimetheus.tif
Telesto.tif
Lapetus2.tif
Janus.tif
Titan.tif
Tethys.tif
Mimas.tif
EnceladusPlumes.tif
EnceladusAndGring.tif
EpimetheusAndJanus.tif
RheaAndTitan.tif
9 km/pixel
2.5 km/pixel
117 m/pixel
796 m/pixel
6 km/pixel
603 km/pixel
641 m/pixel
214 m/pixel
8 km/pixel
448 m/pixel
6 km/pixel
4 km/pixel
613 m/pixel
4 km/pixel
6 km/pixel
2 km/pixel
Rhea:
7 km/pixel
Titan:
14 km/pixel
Titan:
17 km/pixel
Tethys:
12 km/pixel
TethysAndTitan.tif
Size in pixel
Size in km
Shape/Axis
ratio
9. Depending on the time, students have to work on this activity and how the work is organized
(small groups or not), it may be easier to use a macro to open the images of Saturn’s Moons.
Click on “Plugins/Macros/Saturn’s Moons”. The previous images are all opened and tiled
and those displaying a single object are scaled in km.

Beyond the Solar System
1. In order to close all image windows, click on “Plugins/Macro/Close All Image Windows”.
2. Open the image images_power10/BeyondSS/m16.tif with “File/Open” or the “Open Image
File” icon. This is an image taken with the Hubble Space Telescope. It displays gas pillars,
which are part of the "Eagle Nebula" Messier 16, a nearby star-forming region 7,000 lightyears4 away in the constellation Serpens.
3. Zoom in on the top of the columns of gas. Those areas are the birthplace of new stars. The
stars are embedded inside finger-like protrusions extending from the top of the nebula and
produced by a process called "photo-evaporation". Small globules of especially dense gas
are buried within the cloud are thus uncovered and have been named "EGGs" for
"Evaporating Gaseous Globules". The shadows of the EGGs protect gas behind them,
resulting in the finger-like structures at the top of the cloud. Some new stars form in this
process.
4. Knowing that the pixel size is 0.1 arcsec, and the distance to the Eagle Nebula 2 kpc ( =
2,000 pc 5), estimate the size of one EGG. (You can take advantage of the image below).
5. Open the two images “power10/BeyondSS/ref.fts” and “power10/BeyondSS/bpic.fts”.
Compare and describe them.
6. One of the two images shows a circumstellar disk around a star named Beta Pictoris. Try to
display it with a subtraction between the two frames. Use “Process/Image Calculator” to
perform the subtraction between the two images and display the result in a new window.
Click on the “Brightness & Contrast” icon to adjust the threshold to the optimal intensities.
It can be helpful to use the button “set” to set by hand the minimum and maximum values.
7. If you do not succeed to find the circumstellar disk, launch the macro with
“Plugins/Macros/Circumstellar Disk Around Beta Pictoris”.
8. Discuss the ratio between the intensity at the edge of the star and the circumstellar disk.
9. Beta Pictoris is located at 20 pc from the Sun and these images have a resolution of
0.1 arcsec/pixel. Estimate the size of the circumstellar disk.
10. Open the file “power10/BeyondSS/m101.jpg”.
11. Use what you have learned to estimate the diameter of this galaxy.
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1 light year = 9.461 1015m
1 parsec = 1 pc = 3.086 1016 m