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Visibility Tool

This tool plots the visibility of a target on the LCO network in two different ways: seasonal visibility, and daily visibility.


RA and Dec may be entered as decimal degrees (nn.nnn), or hours, minutes, seconds ( for RA and degrees, arcminutes, arcseconds ( for Dec

Seasonal visibility

Daily visibility

Solid lines represent the visibility window; dotted lines represent daytime or hour angle > 4.6. The angle in the legend is the average moon-target distance during the selected night.


Season visibility

Target visibility (as defined below) is shown over the desired range of dates. This is shown as overlapping histograms with one bin per day, (though this may not always be obvious because the bins do not have contours). The vertical axis spans a full day, from midnight UT to midnight UT on the following day. The bottom of a colored bin corresponds to the time in UT at which the target begins to be visible at the site represented by that color. The top of a colored bin corresponds to the time in UT at which the target stops being visible at the site represented by that color. Target airmass and hour angle are calculated every 10 minutes, which should be taken as the uncertainty in bin height.

Overlap of different color histograms indicates time ranges during which the target is visible from multiple sites.

Note that midnight UT occurs during night time at Sutherland, and during part of the year at Cerro Tololo as well. This means that at these sites a target may be visible both at the beginning and at the end of a UT day.

Daily visibility

Target visibility is shown for each site on a given date. The vertical axes correspond to altitude (right-hand side) and airmass (left-hand side).

Visibility is defined by the following constraints:

  • Observations cannot be scheduled at airmass higher than 11.47 (horizon) or hour angle greater than 4.6. Targets above these limits are not viewable. Both visibility plots take those limits into account.
  • The times of sunrise and sunset correspond to nautical twilight (Sun is 12 degrees below the horizon).