Public Event Explorer


open-data fd-camera-viewThe public event display of the Pierre Auger Observatory is hosted at CNEA in Argentina (please note that it does take a while to to load up).

The CNEA website allows browsing over the events collected since 2004, and is updated daily. You can enter an event Id in the search window, search for an event with the event selection menu, or display an event already in cache. You can also download an ascii file with all events.


Guide To Downloading and Formatting Pierre Auger Observatory Data

Guide To Making an Energy Histogram Using Pierre Auger Observatory Surface Detector Data


Downloading and Formatting Data

Guide To Downloading and Formatting Pierre Auger Observatory Data


NOTE: This set of instructions was created using a PC running Microsoft Excel 2007. Some of these instructions will likely be different for Mac users

  1. Go to Event Display
  2. In this page there are several ways to view event data. The way you choose to display this data depends largely on what you wish to accomplish with it. This guide is focused on the use of data for ALL EVENTS
  1. To download data on all events you must click on the ascii file link on the second paragraph. This will download a .txt file containing data for every public event since January 1st 2004. The file should look something like this:

The data may be analyzed using any software of your choosing. Microsoft Excel is a reasonably good choice. The following steps describe how to copy all the data to an Excel File.

  1. Open Microsoft Excel click on the office icon , click and choose the .txt file from the location in which you saved it.
  2. Choose Delimited, since the data fields are separated by spaces in the text file.

  1. Click
  2. In the next screen deselect “Tab” and select “Space”. This will tell Excel to interpret information separated by spaces as separate columns.

In this same window Excel will show a small preview of what the data will look like. Scroll down in this preview window to make sure your data are organized correctly. If your data look as shown in this picture it should be ok

  1. Click and select “General” in the following screen then click

  1. Your data should be neatly organized in a spreadsheet. You’ll notice that the data columns are not directly labeled. What you have is a legend at the top identifying each “field”. Each “field” is essentially a column. If you wish to simplify reading the data you may label the columns directly.

What the data labels mean

  1. Event ID – Every time an event is recorded it is assigned it’s own identification number to help distinguish it from the rest
  2. Number of stations in event – when a cosmic ray produces a shower it “hits” a number of stations in the Auger array of stations.
  3. Theta of incoming cosmic ray– zenith angle
  4. Phi of incoming cosmic ray– azimuth angle
  5. Reconstructed Energy – energy of the original particle that caused the shower in EeV.
  6. Unix time – time elapsed in seconds from January 1st 1970 at 12:00 am to the moment the event was recorded.
  7. Galactic Longitude and Latitude – direction of the original cosmic ray with respect to the Milky Way Plane

Energy Histogram

Guide To Making an Energy Histogram Using Pierre Auger Observatory Surface Detector Data



A histogram is essentially a graphical representation of the frequency or distribution of a variable over specific intervals known as “bins”. In other words is a graph that shows how often a specific number or range of numbers comes up in a data set. This manual focuses on building a histogram that shows the frequency at which the Pierre Auger Observatory Surface Detector has recorded cosmic ray showers of certain energies.


Before you start you should know that:

  • This set of instructions only assumes a very minimal level of proficiency with computers and Microsoft Excel. It is written mostly with teachers in mind not just as a learning tool but as a document that could be adapted for student use.
  • These instructions are written using Microsoft Excel 2007 for PC. Some screens may look different in other versions.
  • In order to complete the following steps you may need to install Data Analysis Tool Pack to Excel. If so you may use Microsoft Office Help options or visit this website and follow their directions.



Download and organize the data

  • Use the instructions in the Data Centre to download the data into an Excel file
  • Go to the “Sheet 1” and “Sheet 2” tabs and rename them “Data” and “Energy Histogram” respectively. This manual will refer to these as spreadsheets. These spreadsheets are all part of the same document and will be saved as such.

First things first! In order to generate a histogram that shows anything meaningful the data must be presented in a log10 scale.
Otherwise the histogram looks like this:

This is not very informative. The axes need to be scaled appropriately so the data get better spread out among more bins.
Our data will have a power distribution so using a log scale will work just fine.


Calculate the log10 of the energy data

  • Label a new column for your log data

  • Type the log10 function in your new column. Apply the calculation to all the energy data

    : the traditional way of applying a calculation to all cells usually involves some kind of “copy/paste” or “drag down” process that due to the large amount of data in your spreadsheet may be inconvenient. Instead try the following trick:

  • Highlight the third cell of any of the other columns. For this example I will chose to use the energy column which is in E3.

  • Press CTRL+SHIFT+DOWN on your keyboard. This will select every number in that column from E3 down.
  • Hit CTRL+C to copy these numbers

  • Select the second cell down in your “log Energy” column which is I3 in this example. Then press CTRL+V to paste the copied data in this column

  • Select the first number in your “log Energy” column. This is the number that was actually calculated in Step 2.

  • Press CTRL+C to copy the log function in this cell then press CTRL+SHIFT+DOWN to select every number in this column then press CTRL+V to paste the log function in every cell in this column. PRESTO you are now ready to create your histogram.

Note: Aside from speeding up the calculation process this also allows you to perform the calculations on only cells that have numbers in them.

  1. Determine the minimum and maximum values in your “log Energy” column – this will help you determine your “Bin” values later
  • Label two new columns in Min and Max

  • Under the “Min” label type the min function then select the first value in the “log Energy” column

  • Don’t close parenthesis yet! Now press CTRL+SHIFT+DOWN to select every value in this column. Press Enter.

  • Repeat this process in the “Max” Column only this time use the Max function instead

  1. Create your “Bins”

The “Bins” are essentially placeholders in the horizontal axis in which Excel will graph a specific range of numbers. For example this manual uses a “Bin Size” of 0.1. This means that any number between 0.1 and 0.2 will be graphed in the same column.

  • For organizational purposes this guide starts the histogram the “Energy Histogram” spreadsheet. Go to this spreadsheet by clicking on the “Energy Histogram” tab created at the beginning of this manual.

  • In your new sheet label a column “Bins”.

  • Fill the “Bins” column with a range of numbers with reasonable increments. Since the Min and Max in this Manual’s example are -0.95713 and 1.61352 respectively we will use bin values starting at -0.9 and ending at 1.6 with 0.1 increments

Note: Choosing the right bins can be tricky depending on the minimum and maximum values of your data and the kind of data distribution desired. Experimenting with the bin values to observe differences in data distribution is recommended.

  1. Find the Frequency of Occurrences
  • Click on the “Data” tab in the Excel menu then click on “Data Analysis”

  • From the pop up menu choose “Histogram” then click “OK”

  • Click on the “Input Range” collapse box. The window will become smaller and will be awaiting your input.

  • Go to the “Data” spreadsheet and select the “log Energy” data by selecting the first cell and using pressing CTRL+SHIFT+DOWN

  • Click the collapse box to return to the input window.

  • Click the the “Bin Range” Collapse box . This process will be similar to the Input range process.
  • Go to the “Energy Histogram” spreadsheet and select the “Bin Range” numbers created in step 4.

  • Click the collapse box to return to the input window.

  • Click the “Output Range” Collapse box . With this you will select the cells you with the data to generate in.
  • Select any reasonable cell in your “Energy Histogram” spreadsheet.

  • Click the collapse box to return to the input window.
  • Click “OK” . Your Frequency Range and bins should appear. This is the data that will be graphed in your histogram.

  1. Generate Graphical Histogram
  • Select the first value in the “Bins” column. DO NOT SELECT BOTH COLUMNS; this will cause the X axis values to be displayed incorrectly.
  • Go to the “Insert” tab in Excel and Click on “Column” in the graph menu, then choose “Clustered Column” from this list. Excel should automatically generate a table.

  • Your graph should look something look this

  1. Insert Titles and Labels
  • Click your graph to select it. Go to the “Layout” tab.
  • Go to “Axis Titles”, select “Primary Horizontal Axis Title” and click on “Title Below Axis”

  • Type in an appropriate name for the Horizontal Axis
  • Repeat this process for the Vertical Axis
  • The Title Can be typed in directly into the graph

  • The amount of detail that can be observed in each axis can also be edited and it mainly depends on the size of the graph. The larger the graph the more detail can be seen. To increase the size of the graph, simply click on the bottom right corner of the graph and while holding the mouse button “drag” the corner of the graph until desired size is obtained.

  • You’ll notice that you now see a larger number of “Bins” on the x axis.

Sensitivity of the Observatory

When observing the histogram, you’ll notice that the graph seems to almost grow linearly and then decreases exponentially. This is due to the sensitivity range of the detector. As the energy of the cosmic ray showers increases the detector becomes more sensitive until it reaches a maximum. When reporting their results scientists only report using the data at which the detector is 100% reliable. The circled section of the graph below is usually ignored when reporting data.

Observatorio Pierre Auger
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Malargüe, Mendoza, Argentina

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