astronomy

Tycho-2 Catalogue

Tycho-2 Catalogue 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 Tycho-2 Catalogue rather than just read about it. In short: The Tycho-2 Catalogue is an astronomical catalogue of more than 2.5 million of the brightest stars. Catalogue The astrometric reference catalogue contain positions, proper motions, and two-color photometric data for 2,539,913 of the brightest stars in the Milky Way.

Key takeaways

Tycho-2 Catalogue belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Tycho-2 Catalogue to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Tycho-2 Catalogue from memory before moving on to harder problems.

Reference excerpt

The Tycho-2 Catalogue is an astronomical catalogue of more than 2.5 million of the brightest stars.

Catalogue The astrometric reference catalogue contain positions, proper motions, and two-color photometric data for 2,539,913 of the brightest stars in the Milky Way. Components of double stars with separations down to 0.8 arcseconds are included. The catalogue is 99% complete to magnitudes of V~11.0 and 90% complete to V~11.5. The Tycho-2 positions and magnitudes are based on the observations collected by the star mapper of the European Space Agency's Hipparcos satellite. They are the same observations used to compile the Tycho-1 Catalogue (ESA SP-1200, 1997). However, Tycho-2 is much larger and a bit more precise, because a more advanced reduction technique was used. The U.S. Naval Observatory (USNO) first compiled the ACT Reference Catalog, (Astrographic Catalogue / Tycho) containing nearly one million stars, by combining the Astrographic Catalogue (AC 2000) with the Tycho-1 Catalogue; the large epoch span between the two catalogues improved the accuracy of proper motions by about an order of magnitude. Tycho-2 now supersedes the ACT. Proper motions precise to about 2.5 milliarcseconds per year are given as derived from a comparison with the Astrographic Catalogue (AC 2000) and 143 other ground-based astrometric catalogues, all reduced to the Hipparcos celestial coordinate system. There were only about 100,000 stars for which proper motion could not be derived. For stars brighter than Vt=9, the astrometric error is 7 milliarcseconds. The overall error for all stars is 60 milliarcseconds. The observational period was from 1989.85 to 1993.21 and the mean satellite observation epoch is 1991.5. Photometric accuracy for stars brighter than Vt=9 is 0.013 magnitude; for all stars it is 0.10 magnitude.

Accessing the catalogue To enable rapid access of specific stars in the catalogue, WCSTools software numbers each star using its Guide Star region number (0001 to 9537) and a five-digit star number within each region, separated by a decimal point. sty2 lists Tycho-2 stars by number or sky region. imty2 lists the Tycho-2 stars within an IRAF or FITS image using the world coordinate system defined in its header. A Perl program for extracting data from the catalogue is available from http://archive.eso.org/ASTROM/. Tycho-2 File Formats WCSTools software uses the files catalog.dat and index.dat.

External resources The following FTP sites make the Tycho-2 catalogue available as 20 gzipped files. After retrieving them and the index.dat file, combine the gzipped files into catalog.dat. The resulting files will differ from the files on the CD-ROM in that they will end lines with only a linefeed, while the CD-ROM version for which WCSTools software was written terminates lines with a carriage return and a linefeed. Add the carriage returns to the files using the unix2dos -ascii command. Put the catalog.dat and index.dat files in a subdirectory data/ to the directory pointed to by the TY2_PATH environment parameter or the ty2cd variable in libwcs/ty2read.c.

Centre de données astronomiques de Strasbourg

Double stars A re-analysis of the original Tycho data in 2002 was used to create a catalogue of multiple stars, the 'Tycho Double Star Catalogue.

See also Hipparcos and Tycho catalogues Gaia (spacecraft) Category:Hipparcos objects Star catalogue

References

External links The Tycho-2 Catalogue The Tycho-2 Catalogue as a CSV dataset

Illustrations

Worked examples

Example 1 — a first encounter with Tycho-2 Catalogue

Start with the simplest possible case. Write down what Tycho-2 Catalogue 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 Tycho-2 Catalogue 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 Tycho-2 Catalogue 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 Tycho-2 Catalogue

In research: Tycho-2 Catalogue 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 Tycho-2 Catalogue 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: Tycho-2 Catalogue is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical catalogues of stars, Hipparcos, so understanding it makes those chapters shorter.
In everyday life: Look for Tycho-2 Catalogue 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 Tycho-2 Catalogue in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Tycho-2 Catalogue 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 Tycho-2 Catalogue out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Tycho-2 Catalogue in simple terms?

The Tycho-2 Catalogue is an astronomical catalogue of more than 2.5 million of the brightest stars. Catalogue The astrometric reference catalogue contain positions, proper motions, and two-color photometric data for 2,539,913 of the brightest stars in the Milky Way.

Why does Tycho-2 Catalogue 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 Tycho-2 Catalogue?

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 Tycho-2 Catalogue.