Hands-On Universe
TM
Asteroid Search
Choosing and Downloading Images Tutorial
As you gaze at the night sky you may not realize just how much space is out there to explore.
For example, if a line were drawn from your southern horizon to your northern horizon
passing through your zenith (the point directly overhead), it would take 172,800
Asteroid Search Images to cover an area one degree wide along that line.
This would require nearly 700 GB of disk space to store these images alone.
Our collection of images is necessarily limited to a fraction of that space.
We discover asteroids by comparing images of the same region of the sky taken at different
times - typically less than an hour apart. We will show you how to compare two such images
to locate a moving object: the object is observed at one location in the first image and is
observed at a slightly different location in the second image. We may be able to locate the
object in yet another image, and so on.
In that way we build up a collection of observations of an object that - since it appears to
be the same object moving from one place to another
- is a good candidate for identification as an asteroid.
So we start with at least two images. And, typically, in the HOU Asteroid Search,
we examine images taken at the same telescope with the same camera
and with the same CCD detector
(the CCD "Charge Coupled Device" collects the light from which the images are made).
This ensures that the observing characteristics are the same for all images.
HOU Asteroid Search images derive from one of two collections: the Big Throughput Camera
collection and the Deep Lens Survey collection. Typically, you will be downloading and
comparing images from one of these collections, to make sure the images are from the same
telescope, camera, and CCD combination, as just explained.
The next section guides you through the process of selecting and downloading
asteroid candidates from the HOU Asteroid Search collection of images.
- Click the 'Download Images' button in the left sidebar of the
Asteroid Search Home Page.
to begin the process of selecting an image to download.
- You will see a list of observing runs; seven are labelled "DLS" and one is labelled
"BTC".
- Select an observing run. NOTE: The "field of view"
(the area of the sky imaged at one time) is dependent on the Telescope/CCD System.
Therefore you should only compare images which have been taken
by the same Telescope/CCD Camera system.
-
Once you have selected a Telescope/CCD Camera system, you will be asked for the
RA and Dec of the area you wish to search. In addition you will also see the button
"Areas (RA/Dec) Imaged". Clicking on this button will take you to a list of areas
(RA/Dec Coordinates) which have images available. Because of our limited database,
we suggest you choose an area from this list.
NOTE: It is strongly suggested that you choose coordinates (RA/Dec) from the list
provided since we do not have images for most other parts of the sky.
After inputing the desired RA/Dec of the area you wish to search, select the "Enter"
button. This will take you to a 5 X 5 table. The center block of the table corresponds
to the area (RA/Dec) you selected and the surrounding blocks correspond to the area
of the sky surrounding your chosen area.
-
Click on the block at the center of the table. This will take you to a listing of
image files available for the area (RA/Dec) of the sky you have selected. At this
point you should see a listing of files which looks similar to this:
- 013427+1523_970214_0224_V.fts
- 013427+1523_970214_0457a_V.fts
- 013427+1524_960902_0145c_V.fts
- 013427+1524_960902_0345_V.fts
- 013427+1525_970215_0123d_V.fts
- 013427+1525_970215_0353_V.fts
- 013427+1525_970219_0032b_V.fts
- 013427+1525_970219_0215b_V.fts
-
This is what the file name indicates about the image:
IMPORTANT:
The "Section" code (a, b, c, or d) denotes a section of a BTC image.
A full-field BTC image is about 8MB.
When you click one of these full-field BTC images you will be given the option of
downloading either the full-field image or a section of that image.
A section (1/4 of a full-field BTC image) is about 2MB, as shown here:
The images from the Deep Lens Survey ("DLS")are 8MB sections of original 134MB images.
The DLS sections are not subdivided, so you will not see section indicators such
as a, b, c, or d in the name of a DLS image.
A DLS section is about the same size as a full-field BTC image.
Now that you have an understanding of what each file name means, click on the file
you wish to download. This will take you to the final level where you have the option
of downloading either the full field image or a section of it. Simply click on the full
field image or the corresponding section you wish to download.
