astronomy

Guide Star Catalog

Guide Star Catalog 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 Guide Star Catalog rather than just read about it. In short: The Guide Star Catalog (GSC), also known as the Hubble Space Telescope, Guide Catalog (HSTGC), is a star catalog compiled to support the Hubble Space Telescope with targeting off-axis stars. GSC-I contained approximately 20,000,000 stars with apparent magnitudes of 6 to 15.

Key takeaways

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

Reference excerpt

The Guide Star Catalog (GSC), also known as the Hubble Space Telescope, Guide Catalog (HSTGC), is a star catalog compiled to support the Hubble Space Telescope with targeting off-axis stars. GSC-I contained approximately 20,000,000 stars with apparent magnitudes of 6 to 15. GSC-II contains 945,592,683 stars out to magnitude 21. As far as possible, binary stars and non-stellar objects have been excluded or flagged as not meeting the requirements of Fine Guidance Sensors. This is the first full sky star catalog created specifically for navigation in outer space.

History

Version 1.0 The first version of this catalog was published in 1989. The first catalog was created by digitizing photographic plates produced by the Palomar Schmidt Quick-V survey for the northern hemisphere and the UK Schmidt SERC-J survey for the southern hemisphere. This catalog contains objects in the magnitude range 7-16 and the classification was biased to prevent the use of a non-stellar object as a guide star. The photometry is based on a photoelectric sequence (9-15th mag) near the center of each Schmidt plate. Stellar photometry was performed in a manner that would systematically reject galaxies. Astrometry was determined using the AGK3, SAOC or CPC catalog stars depending on plate declination. Although the relative astrometry (required for HST) is about 0.3 arc seconds, there are known systematic errors near the plate edges of 1 to 2 arc seconds.

Version 1.1 The first revision of the catalog was published in 1992. The Tycho Input Catalog was created by the Hipparcos/Tycho international consortia in preparation for the Hipparcos satellite mission. They produced a catalog containing the best available data for all stars to magnitude 11. Adding the bright star data from this catalog to the GSC produced a complete all-sky catalog down to the GSC limiting magnitude. In addition, many of the false objects due to artifacts around the halos and diffraction spikes of the bright stars were identified and corrected as well as a number of reported errors. A number of astrographic plates centered on southern hemisphere bright stars (of magnitude less than 3) were also processed and added to the catalog. This was the version used by HST operations prior to cycle 15.

Version 1.2 Version 1.2 was published in 2001. It was produced in collaboration with the Astronomisches Rechen-Institut in Heidelberg. This version reduces the plate-based position-dependent and magnitude-dependent systematic errors. The PPM and AC reference catalogs were used and absolute position errors have been reduced to between 0.3 and 0.4 arc seconds.

Catalog format When quoting a catalog entry, the format is GSC FFFFF-NNNNN, or alternately, GSCfffff0nnnnn (fffff0nnnnn). The F-sequence references a Hubble sky region code.

Guide Star Catalog II A significant expansion of the catalog, Guide Star Catalog II, was published in 2008. The Guide Star Catalog II (GSC-II) was compiled by the Catalog and Surveys branch of the Space Telescope Science Institute and the astrometry team of the Astronomical Observatory of Torino (Italy). It has entries for 945,592,683 stars, and has positions, classifications, and magnitudes for 455,851,237 stars. The latest revision of this version (2.3.4) is in active use for accurately positioning the Hubble Space Telescope.

See also Hubble Guide Star Catalog - Astrographic Catalog/Tycho (GSC-ACT) Hubble Space Telescope Space Telescope Science Institute Star catalog Fine Guidance Sensor (HST)

References

External links GSC I and GSC II home GSC II

Worked examples

Example 1 — a first encounter with Guide Star Catalog

Start with the simplest possible case. Write down what Guide Star Catalog 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 Guide Star Catalog 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 Guide Star Catalog 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 Guide Star Catalog

In research: Guide Star Catalog 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 Guide Star Catalog 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: Guide Star Catalog is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical catalogues of stars, Hubble Space Telescope, so understanding it makes those chapters shorter.
In everyday life: Look for Guide Star Catalog 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 Guide Star Catalog in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Guide Star Catalog 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 Guide Star Catalog out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Guide Star Catalog in simple terms?

Why does Guide Star Catalog 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 Guide Star Catalog?

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 Guide Star Catalog.