astronomy

NASA Infrared Telescope Facility

NASA Infrared Telescope Facility is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand NASA Infrared Telescope Facility rather than just read about it. In short: The NASA Infrared Telescope Facility (NASA IRTF) is a 3.2-meter (10 ft) telescope optimized for use in infrared astronomy and located at the Mauna Kea Observatory in Hawaii. It was first built to support the Voyager missions and is now the US national facility for infrared astronomy, providing continued support to planetary, solar neighborhood, and deep space applications.

Key takeaways

NASA Infrared Telescope Facility belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect NASA Infrared Telescope Facility to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of NASA Infrared Telescope Facility from memory before moving on to harder problems.

Reference excerpt

The NASA Infrared Telescope Facility (NASA IRTF) is a 3.2-meter (10 ft) telescope optimized for use in infrared astronomy and located at the Mauna Kea Observatory in Hawaii. It was first built to support the Voyager missions and is now the US national facility for infrared astronomy, providing continued support to planetary, solar neighborhood, and deep space applications. The IRTF is operated by the University of Hawaii under a cooperative agreement with NASA. According to the IRTF's time allocation rules, at least 50% of the observing time is devoted to planetary science.

Telescope

The IRTF is a 3.2 m (126") classical Cassegrain telescope. The Cassegrain focus f/ratio is f/38 and the primary mirror f/ratio is 2.5. Several aspects of the design of IRTF are optimized for IR observations. The secondary mirror is undersized to prevent the instrument from seeing the thermal emission from the telescope structure around the primary mirror. A small mirror in the center of the secondary mirror prevents the instrument from seeing its own thermal emission. The f/ratio is long to have a small secondary mirror, again to minimize the telescope's thermal emission. The mirror coatings are chosen to have minimal thermal emission. The emissivity of the telescope is usually below 4%. The secondary mirror is mounted on a chopping mechanism to rapidly switch the pointing of the telescope from target to sky at up to 4 Hz. The IRTF is mounted on a large English yoke equatorial mount. The mount is very stiff, reducing flexure and allowing for accurate pointing of the telescope. Since the telescope is on an equatorial mount, the telescope can observe targets through the zenith without concern for field rotation. The yoke mount prevents the telescope from pointing north of +69 degrees declination. Since the telescope was primarily intended for planetary science, this restriction was considered to be acceptable. Since the telescope is on a heavy mounting, it is relatively immune from vibration or wind shake.

Instrumentation The IRTF hosts three facility instruments: SpeX/MORIS, iSHELL, and MIRSI/MOC. IRTF also hosts a number of visiting instruments.

SpeX SpeX is a medium-resolution 0.7-5.4 μm spectrograph built at the Institute for Astronomy (IfA), for the NASA Infrared Telescope Facility (IRTF) on Mauna Kea. The primary scientific driver of SpeX was to provide maximum simultaneous wavelength coverage at a spectral resolving power which is well-matched to many planetary, stellar and galactic features, and at resolving power which adequately separates sky emission lines and disperses sky continuum. This requirement has resulted in an instrument which provides spectral resolutions of R~1000-2000 across 0.8-2.4 μm, 2.0-4.1 μm, and 2.3-5.5 μm, using prism cross-dispersers (15 arcsec-long slits). Single order long slit (60 arcsec) modes are also available. A high throughput prism mode is a provided for 0.8-2.5 μm spectroscopy at R~100 for solid state features and SEDs. A Teledyne 2048x2048 Hawaii-2RG infrared detector array is used in the spectrograph. SpeX also contains an infrared slit-viewer/guider covering a 60x60arcsec field-of-view at 0.12arcsec/pixel. A Raytheon Aladdin 2 512x512 InSb array in the infrared slit-viewer. The infrared slit viewer can also be used for imaging or photometry. SpeX is used for a wide array of planetary and astrophysical research programs and is the most requested instrument on IRTF. MORIS is a CCD camera fed by a dichroic in SpeX. It is used for visible imaging and as a visible guider for SpeX.

iSHELL iSHELL is a 1 - 5.3 μm high resolution cross-dispersed echelle spectrograph which uses a 2048x2048 Hawaii-2RG infrared detector array. It replaced CSHELL; by using a larger array and a cross disperser, iShell has much larger wavelength coverage per setting than did CSHELL. iShell uses a silicon immersion grating to achieve a high dispersion with a relatively small grating, which in turn allows the optics and the whole instrument to be much smaller than if it used a conventional grating. Thus, despite having much higher spectral resolution than SpeX, iShell will be slightly smaller. There will be two immersion gratings, one optimized for K band and one optimized for L band. Due to the silicon grating, iShell will not be sensitive to light shorter than 1 μm. Each pixel is 0.125" on the sky and the spectroscopic dispersion is 80,000 when used with a 0.375" slit. Five slits from 0.375" to 4.0" are available for use. iSHELL also has an IR imaging mode and IR guiding camera, which covers a 42" diameter field. As of 2019, iSHELL was the second-most heavily used instrument at IRTF (after SpeX).

MIRSI MIRSI is a 2.2 to 25 μm thermal infrared imaging camera with grism spectrographic capability. MIRSI was built by Boston University and upgraded by IRTF staff. The optics operate at 20k and the 320x240 Si:As BIB detector at 5K with cooling from a Sumitomo closed-cycle cooler. MIRSI has a selection of broad-band and narrow-band filters, as well as a CVF. MOC is a CCD camera fed by a dichroic in MIRSI. Simultaneous visible and MIR photometry with MOC and MIRSI is used to measure asteroid albedos and hence sizes.

MORIS MORIS (MIT Optical Rapid Imaging System) s a high-speed, visible-wavelength camera for use on IRTF using an electron multiplying CCD. MORIS is mounted on the side window of SpeX, and is fed by the internal cold dichroic in SpeX. The design is based on POETS (Portable Occultation, Eclipse, and Transit Systems), which were developed by a collaboration between MIT and Williams College. MORIS is available for open use on IRTF and its user interface has been converted to the IRTF standard interface. In addition to visible light photometry, MORIS is also used as a visible light guider for SpeX, allowing guiding on targets as faint as V=20. The guiding software includes atmospheric dispersion correction to move the visible light guide box to keep the IR image on the SpeX slit.

Visiting instruments IRTF also hosts a number of visitor instruments, usually thermal infrared spectrographs. These have included TEXES, EXES, BASS, and HIPWAC.

Future instruments The IRTF staff are currently developing SPECTRE, a one-shot 0.4 - 4.2 μm seeing-limited integral field unit R=150 spectrograph .

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Illustrations

Worked examples

Example 1 — a first encounter with NASA Infrared Telescope Facility

Start with the simplest possible case. Write down what NASA Infrared Telescope Facility claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to NASA Infrared Telescope Facility before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about NASA Infrared Telescope Facility ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of NASA Infrared Telescope Facility

In research: NASA Infrared Telescope Facility appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses NASA Infrared Telescope Facility in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: NASA Infrared Telescope Facility is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical observatories in Hawaii, Buildings and structures in Hawaii County, Hawaii, Infrared telescopes, so understanding it makes those chapters shorter.
In everyday life: Look for NASA Infrared Telescope Facility outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study NASA Infrared Telescope Facility in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NASA Infrared Telescope Facility means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain NASA Infrared Telescope Facility out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NASA Infrared Telescope Facility in simple terms?

Why does NASA Infrared Telescope Facility matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study NASA Infrared Telescope Facility?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on NASA Infrared Telescope Facility.