nadir zenith

Image Credit: ESO/S. Brunier

Figure 1.

Sky Frame:
Galactic coordinates:

This image shows the entire sky, viewed from Earth. Our galaxy, the Milky Way, is the dominant feature (click the "Hide All" button to the right), with the galactic center at the center of the image and the galactic plane aligned horizontally. The image spans the full 360 degrees of galactic longitude ranging from 180 to 0 degrees from extreme left to the center, and from 0 to -180 degrees from the center to the extreme right. The vertical direction spans -90 to +90 degrees galactic latitude from bottom to top. Since we want to include the maximum number of stars in each scan, we're limiting our search to galactic latitudes near the galactic plane where most of the stars in our galaxy can be found. Our search will be limited to the region of sky between the two horizontal dashed lines (uncheck the "SETI survey limits" box to the right) in this image, at -5 and +5 degrees galactic latitude.

At any given time, only half of the sky can be seen from a fixed point on Earth, such as the location of the DSS28 telescope. Anything below the horizon (sub-horizon) at the location of the DSS28 antenna can't be observed (by DSS28). Since the Earth is rotating on it's axis but the background of stars is not, the portion of the galaxy which is visible changes with time, so you'll have to pick a sky frame which covers a portion of the sky which is visible for the duration of your observation.

The idealized horizon at the location of the DSS28 telescope, disregarding terrain features like mountains, is shown as a white curve (uncheck the "Horizon at ts" box). The position of the horizon 40 minutes (about the time require to scan a sky frame) after the specified time is shown as a gray curve (uncheck the "Horizon at ts+40" box). The obstructed part of the sky in each case (i.e., below the horizon at that time) is shaded in red. Markers are shown for the nadir and zenith points at DSS28 (uncheck the "Nadir marker" and "Zenith marker" boxes). The zenith point is directly overhead and nadir is directly below the telescope location (looking straight down toward the center of the Earth).

Image Credit: NASA/JPL-Caltech

Figure 2. This is an artist's representation of our current (as of 2008) understanding of the large-scale structure of our Milky Way galaxy, if we could view it from high above the galactic plane. The location of our solar system (including the Sun, Earth, and the DSS28 telescope) is indicated by the white "x".

During a typical SETI observation, the DSS-28 telescope scans a selected small patch of sky we refer to as a sky frame. As you move your cursor over Figure 1 (within our SETI survey limits), the sky frame number is displayed in the box above, the sky frame is outlined in Figure 1 (you'll have to zoom in to see this) and the highlighted region in Figure 2 indicates the direction and galactic longitude coverage of the sky frame scan.

If you instead move your cursor over Figure 2, you are selecting the longitudinal direction of the scan. However, a direction in Figure 2 can't uniquely determine the sky frame because there is no latitude information in the figure. Therefore, a vertical band is highlighted in Figure 1 showing the longitude range that will be covered by a scan but without identifying a specific sky frame within the latitude range of our search region.

Plan Your Scan

Pick the date and time of your scheduled observation to reveal the part of the sky from which you'll be able to select a sky frame to scan.

Start Date/Time

Set/Update to current time

User-specified Time







Date/Time of Displayed View







Rate of Simulated Time Passage


100 times normal

1000 times normal


Obstructed sky at ts

Obstructed sky at ts+40

SETI survey limits

Zenith marker

Nadir marker

Previous scan coverage

ts is the simulation time (the time shown under the "Date/Time of Displayed View" heading)
ts+40 is 40 minutes (the time required for a standard sky frame scan) after the simulation time ts