Identificación de asteroides cercanos a la Tierra
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Frequently Asked Questions

1) What are the needed system requirements?

The only requirement is for you to have Java installed on your computer.  This is necessary because to view the images a program called Aladin is needed, which uses Java. There is no need to install Aladin, as it launches from within your web browser. However, you must ensure you have the Sun-Oracle version, as the other version may not work correctly. For Ubuntu (Linux) users, an installation guide is available with instructions on how to install Java, as well as choosing which Java version is to be installed.

2) I already have a password. What do I do now?

Go to the system’s main page and type in your username and password to log in. Once this is done you can visit the “Help” section if you require any further information or visit the “Asteroids” section if you feel confident enough to start identifying asteroids.

3) Is there a blog/forum to discuss opinions and comments with other users?

Unfortunately, there isn’t one at this point in time. However, we hope to have one soon.

4) I’m already in the “Asteroids” section. What do I have to do to start identifying asteroids?

Choosing an Object

Once you’re in the “Asteroids” section you will see a list of objects with potential discoveries from which you must choose one. Upon clicking on the object, a list with all the images from the SDSS (Sloan Digitized Sky Survey), in which the object is likely to be in, will appear.

  • Images appear grouped in bundles of up to 5 images from the same sky zone,  taken at slightly different times (a couple of minutes apart) and at different photometric bands (i.e. at different wavelengths)
  • For each image, a table with the following information will be displayed
    • Band (r,i,u,z,g photometric bands)
    • MJD (Modified Julian Date of the observation)
    • RA, DEC (Position in which the object is meant to be at the time of the observation)
    • Mag (apparent magnitude expected from the object)
  • There will also be an empty RA/DEC field where the default object status will be “---“. Filling these fields in is your task.

Visual Inspection

The task in hand is to check if the asteroid is in fact in the image (in some cases it may be too faint to detect, or even out of the image) and to measure its exact position. In order to do this you must click on the link “View with Aladin”.

  • Once you have clicked on this link, the Aladin applet should launch. Aladin is a Java app developed by the Strasbourg astronomical Data Centre (CDS), which, amongst other things, allows the user to work with images from the Virtual Observatory. In order to do this, a framework called webstart is used, which essentially downloads the Java app on your computer from the CDS server.
  • IMPORTANT: In order to open the applet directly with this link, once the browser asks you what to open the app with, you should choose “Java webstart by Sun”. Other webstarts will launch Aladin, but will not execute the appropriate commands.
  • If this step works correctly, Aladin will launch and the corresponding images will load (this may take a while depending on the speed of your connection, although information will be displayed detailing what image is being loaded and what percentage has been completed). Once loaded, the approximate position of the object will appear. You will be able to see a slight shift in the object’s position with respect to other images, while other points, such as stars, will remain stationary, effectively showing that the point that has moved is the asteroid.
  • Certain tools such as “zoom” (right) or “match” (bottom) may aid your inspection.

Saving Data in the System

Once the position of each object (RA and DEC) has been found, return to the website and follow these instructions:

  1. Fill in the information in the RA/DEC field, separating the values with a space.
  2. Change the status to “confirmed”. If the object cannot be seen in the image, change the status to either “too faint” or “outside of the image”
  • Too faint: This is not uncommon, especially in the “u” band.
  • Out of field: At times, asteroid’s orbits are not known to a high precision, which may lead to the estimated position being quite far from the real one. This is particularly true for asteroids discovered recently (2011 onwards) due to the lack of associated observations, leading to high uncertainties in their orbits. For example, 2011HS54 only has 7 observations to date, taken over a spread of two days, which totally insufficient data as to obtain precise orbital parameters. Therefore, it is likely that the position given as an estimate is very far from its real position. In these scenarios, if no objects can be seen displaying apparent movement, it is best to change their status to “out of field”.

It is not necessary for you to do this process for every group of images of an object, although it is compulsory for you to do this for every image from a specific group. Once a whole group has been done, click on “Save Data” and the information will be saved in the system. This information will then be checked by personnel of the Spanish Virtual Observatory, and, if found to be correct, sent to the Minor Planet Centre, who will publish it in one of their electronic bulletins and will use it to refine their orbital parameters of the asteroid. As well as this, it will be noted that you have found this information, and will also appear in the “Hall of Fame” section in our website.

To get information on this process in more detail, follow the “Step by step example”.

5) How can I obtain a statistic on the images that I have worked with and the asteroids I have identified?

Every time you log in, the system will show a summary of all the images you have worked with and their current statuses. You can access this information at the “Summary” section .

6) If I take incorrect readings, will I lose my account?

Of course not. Most users will never have some something similar and it is perfectly understandable for people to make mistakes, especially on their first couple of times. In fact, the system takes this into account and only displays results if a significant number of people agrees on the same results.

However, if a user were to not use the system properly, saving random data for example, the possibility of losing that account would exist.

7) If the object is long, round or large, what bit of the dot should I use to mark its position?

As a general guideline, it is best to point at the middle of what looks to be an asteroid. If it is a “fat dot”, use the middle of the point and if it is a long dot i.e. line shaped, use the midpoint. The idea is for the MJD of the observation which appears in table of data to be the mid-time of the observation, i.e. the middle of the dot.

Some graphic examples:


8) If the asteroid can’t be found in the image, when should the status be “too faint” and when “out of field”?

See examples.

9) I’m having trouble using Aladin in Chrome, what should I do?

Some users have reported this problem as well and the problem seems to be chrome not recognising .jnlp files. Try Internet Explorer or Mozilla Firefox, or contact us at

10) When launching Alading, the applet runs but the images don’t load. Is the version of Aladin outdated? What can I do?

The problem actually lies with Java, and therefore webstart, not with Aladin. When you click on the link we provide, a .jnlp file is sent, which contains two pieces of information: What remote app needs to be launched (Aladin) and what specific set of instructions needs to be sent. Your computer tries to open this file with webstart. However, for some reason, not all versions of Java send the correct instructions to Aladin, and instead only launch the app without telling it what to do.

This problem may occur depending on your operative system and/or the version of Java you’re running. We’ve found version 1.8 by Sun/Oracle may lead to problems in Linux, although most users report version 1.8 works in Windows.

By default, Windows comes with its own version of Java. Some users have reported problems with the Windows 8 version of Java, but not with 7. If you do encounter any problems, you could try downloading the Sun version of Java at (click on “do I have Java?” to check if you are unsure as to whether you have installed this version of Java or not).

11) In my Summary section I can see the detailed information of my measurements. However, when I click on “Search in the ADS” no results are shown.

This problem has occurred for some collaborators. It seems as though ADS cuts the authors list short when it is too long. We have contacted them and are waiting for their response.

Of course, this doesn’t mean that the data supplied has not been used for the project. A detailed description of how useful your work is, is given under the “Summary” section.

12) I can’t find anything in the estimated position but I can find an object that moves in a position further away. I can measure its position but the app doesn’t allow the data to be saved, as it is “too far from the estimated position”. What should I do?

It is possible that for a given image, more than one asteroid shows up in positions very far from the estimated one. These objects should not be taken into account as they don’t correspond to the asteroid that we are trying to locate. If it is a NEA (near-Earth asteroids) it will feature in the list we provide you with, and if it is a main belt asteroid, which is the more likely out of the two, it should be ignored as this program is only interested in identifying NEAs.

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