Monthly time use

Non-sidereal target observations

Beginning in late 2023 the HET has begun supporting a limited mode of non-sidereal observations. As we expect this mode to be utilized by a limited number of users in relatively specialized cases, it has not yet been incorporated into TSL. If you require non-sidereal observations, please contact the Resident Astronomers at astronomer@het.as.utexas.edu in advance of your institution's proposal deadline to discuss and coordinate.

Briefly, our technical approach to this limited non-sidereal tracking is to use one of our guide cameras to move the guide star fiducial in an equal and opposite direction to the target's non-sidereal motion. This will drag the telescope along the sky at the same rate as the non-sidereal object. We are limited to the ~20" field of view of the guide cameras, but should be able to observe at least ~10" of motion (more with careful coordination). Given the maximum track length of 72 minutes for objects on the ecliptic (at Dec = +23deg), 10" of motion is adequate for the Jovian and Saturnian satellites (the intended targets of our observations).

As mentioned, there is no way to request this mode in TSL, so we advise that you do the following:

1. Contact astronomer@het.as.utexas.edu to discuss your science needs/plans and we will help you.

2. Submit your proposal to your TAC, and get an approved program in the queue.

3. In coordination with the RAs, generate a list of targets for the nights when you anticipate the target to be observed, and its coordinates at the time it is available, with SYNDATE restrictions for each night.
    For example, if you were hoping to observe Enceladus during the month of May 2024, you might submit something like this in your TSL file's TRACK_LIST block:

OBJECT             RA         DEC          SYNDATE
Enceladus_20240501 23:12:24.4 -07:00:05.2  =20240501
Enceladus_20240502 23:12:47.5 -06:58:18.3  =20240502
Enceladus_20240503 23:13:05.6 -06:56:25.7  =20240503
... etc

4. Make sure the RAs are aware of your target in the queue, and if necessary, help generate an Ephemeris file (e.g. from https://ssd.jpl.nasa.gov/horizons/app.html#/) that has high time resolution for the target's coordinates as observed from McDonald Observatory. In our testing we used 1-minute time steps, but depending on the object's speed 5- or 10-minute steps may also be fine.

On the night your target will be observed, the RA will use a script called "nst.py" to interpolate the ephemeris file to the exact moment when the guider camera is activated and apply non-sidereal corrections at a specified time step. We've done this with 1-minute updates in our tests, but again depending on the motion of your target it might be fine to do 2-minute or longer as well.

Further technical details are available on our internal page here:

Basically we are excited to help support your non-sidereal observing requests! Our approach is limited in its capabilities for now, but can be developed further if additional needs arise.

Last updated: Tue, 23 Jan 2024 15:58:55 +0000 stevenj


The Telescope

Technical Overview

Object Observability


Non-sidereal observations



LRS2 Summary

LRS2 Details

LRS2 Fiber Layout and Position Angle

LRS2 Throughput

LRS2 Observing details


VIRUS - Summary

VIRUS - Setting up on targets

VIRUS - Misc details

VIRUS - Throughput and sensitivity

VIRUS - low surface brightness sensitivity

VIRUS - Dithers, IFUs, Tiling

VIRUS - Tiling observations

Habitable Zone Planet Finder (HPF)

HPF Details

HPF Setting up on targets

HPF Throughput and Exposure Meter

HPF Data Reductions

HRS-2 (in development)

HRS-2 Summary

HRS-2 Details

HRS-2 configurations

HRS-2 exposure meter

HRS-2 Position Angle and Fiber layout

HRS-2 Throughput

Old Instruments

HRS - old

LRS - old

MRS - old

Program Preparation

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