HET Object Observability

Useful CGI scripts

  • Try our Object Observability and Feasibility Calculator .

  • See when the HET can observe your target, i.e. the first date when fully half of a target's eastern trajectory is observable just before dawn 18 degree twilight, until the last date when fully half of its western trajectory remains observable just before dusk 18 degree twilight.

  • Determine the longest possible track time for your target.

  • To get the specific dates over an entire year when a target is available try our yearlong observing calendar, or try our trimester-based observing calendar.

  • To see the effect of changing exposure times in a moving aperture try the HET Filling Factor Calculator.

    The Theory

    Because the HET has a fixed elevation of 55°, and a tracking radius of 8.4°, it can only observe objects that fall within a certain zenith distance. This means that the air mass with the tracker centered will always be 1.222. Translating to astronomical coordinates, we derive the following target accessibility locus on the sky:

    Objects are available within the region between the inner and outer limiting altitude curves. The maximum track time occurs at a declination of 63°. The length of time a given object can be observed varies with declination and telescope azimuth. The following figure shows the maximum time that can be spent on an object at a given declination with the telescope at the optimal azimuth:

Last updated: Sun, 08 Jan 2012 01:56:11 -0600 caldwell


The Telescope

Technical Overview

Object Observability




HRS Instrument Summary

HRS - Details

HRS Configurations

HRS Throughput

HRS Wavelength Calibration


MRS Instrument Summary

MRS Configurations

MRS Throughput

MRS Wavelength Calibration


LRS Instrument Summary

LRS Configurations

Multi-object Unit

LRS Throughput

LRS Spectral Resolution

LRS Wavelength Calibration

Visitor Filter Information

LRS Position Angles

Blind Offsetting

Guide Stars Limits

LRS Update from Gary Hill

Program Preparation

Web Management System

Other HET Documentation