astronomy

ROSAT

ROSAT 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 ROSAT rather than just read about it. In short: ROSAT (short for Röntgensatellit; in German X-rays are called Röntgenstrahlen, in honour of Wilhelm Röntgen) was a German Aerospace Center-led satellite X-ray telescope, with instruments built by West Germany, the United Kingdom and the United States. It was launched on 1 June 1990, on a Delta II rocket from Cape Canaveral, Florida, on what was initially designed as an 18-month mission, with provision for up to five…

Key takeaways

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

Reference excerpt

ROSAT (short for Röntgensatellit; in German X-rays are called Röntgenstrahlen, in honour of Wilhelm Röntgen) was a German Aerospace Center-led satellite X-ray telescope, with instruments built by West Germany, the United Kingdom and the United States. It was launched on 1 June 1990, on a Delta II rocket from Cape Canaveral, Florida, on what was initially designed as an 18-month mission, with provision for up to five years of operation. ROSAT operated for over eight years, shutting down on 12 February 1999. In February 2011, it was reported that the 2,400 kg (5,291 lb) satellite was unlikely to burn up entirely while re-entering the Earth's atmosphere due to the large amount of ceramics and glass used in construction. Parts as heavy as 400 kg (882 lb) could impact the Earth's surface. ROSAT eventually re-entered the Earth's atmosphere on 23 October 2011 over the Bay of Bengal.

Overview The Roentgensatellit (ROSAT) was a joint German, U.S. and British X-ray astrophysics project. ROSAT carried a German-built imaging X-ray Telescope (XRT) with three focal plane instruments: two German Position Sensitive Proportional Counters (PSPC) and the US-supplied High Resolution Imager (HRI). The X-ray mirror assembly was a grazing incidence four-fold nested Wolter I telescope with an 84-cm diameter aperture and 240-cm focal length. The angular resolution was less than 5 arcsecond at half energy width (the "angle within which half of the electromagnetic radiation" is focused). The XRT assembly was sensitive to X-rays between 0.1 and 2 keV (one thousand Electronvolts). In addition, a British-supplied extreme ultraviolet (XUV) telescope, the Wide Field Camera (WFC), was coaligned with the XRT and covered the energy band from 0.042 to 0.21 keV (30 to 6 nm). ROSAT's unique strengths were high spatial resolution, low-background, soft X-ray imaging for the study of the structure of low surface brightness features, and for low-resolution spectroscopy. The ROSAT spacecraft was a three-axis stabilized satellite which can be used for pointed observations, for slewing between targets, and for performing scanning observations on great circles perpendicular to the plane of the ecliptic. ROSAT was capable of fast slews (180 deg. in ~15 min.) which made it possible to observe two targets on opposite hemispheres during each orbit. The pointing accuracy was 1 arcminute with stability less than 5 arcsec per sec and jitter radius of ~10 arcsec. Two CCD star sensors were used for optical position sensing of guide stars and attitude determination of the spacecraft. The post facto attitude determination accuracy was 6 arcsec. The ROSAT mission was divided into two phases:

After a two-month on-orbit calibration and verification period, an all-sky survey was performed for six months using the PSPC in the focus of XRT, and in two XUV bands using the WFC. The survey was carried out in the scan mode. The second phase consisted of the remainder of the mission and was devoted to pointed observations of selected astrophysical sources. In ROSAT's pointed phase, observing time was allocated to Guest Investigators from all three participating countries through peer review of submitted proposals. ROSAT had a design life of 18 months, but was expected to operate beyond its nominal lifetime.

Instruments

X-ray Telescope (XRT) The main assembly was a German-built imaging X-ray Telescope (XRT) with three focal plane instruments: two German Position Sensitive Proportional Counters (PSPC) and the US-supplied High Resolution Imager (HRI). The X-ray mirror assembly was a grazing incidence four-fold nested Wolter I telescope with an 84 cm (33 in) diameter aperture and 240 cm (94 in) focal length. The angular resolution was less than 5 arcsec at half energy width. The XRT assembly was sensitive to X-rays between 0.1 and 2 keV.

Position Sensitive Proportional Counters (two) (PSPC) There are two Position Sensitive Proportional Counters (PSPC), PSPC-B and PSPC-C, mounted on a carousel within the focal plane turret of ROSAT. PSPC-C was intended to be the primary detector for the mission and was used for the bulk of the All-Sky Survey until it was destroyed during the AMCS glitch on 25 January 1991. After the glitch, PSPC-B was used for all further observations. Two more PSPCs (PSPC-A and PSPC-D) were mounted on ROSAT for ground calibration. Each PSPC was a thin-window gas counter. Each incoming X-ray photon produced an electron cloud whose position and charge were detected using two wire grids. The photon position was determined with an accuracy of about 120 micrometers. The electron cloud's charge corresponded to the photon energy, with a nominal spectral bandpass 0.1-2.4 keV.

High Resolution Imager (HRI) The US-supplied High Resolution Imager used a crossed grid detector with a position accuracy to 25 micrometers. The instrument was damaged by solar exposure on 20 September 1998.

Wide Field Camera (WFC) The Wide Field Camera (WFC) was a UK-supplied extreme ultraviolet (XUV) telescope co-aligned with the XRT and covered the wave band between 300 and 60 angstroms (0.042 to 0.21 keV).

Highlights

X-ray all-sky survey catalog, more than 150,000 objects. XUV all-sky survey catalog (479 objects). Source catalogs from the pointed phase (PSPC and HRI) containing ~ 100,000 serendipitous sources. Detailed morphology of supernova remnants and clusters of galaxies. Detection of shadowing of diffuse X-ray emission by molecular clouds. Detection of pulsations from Geminga. Detection of isolated neutron stars. Discovery of X-ray emission from comets. Observation of X-ray emission from the collision of Comet Shoemaker-Levy with Jupiter.

Catalogues 1RXS – an acronym which is the prefix used for the First ROSAT X-ray Survey (1st ROSAT X-ray Survey), a catalogue of astronomical objects visible for ROSAT in the X-ray spectrum.

Illustrations

ROSAT: Earth's Moon on 29 June 1990 by ROSAT — Earth's Moon on 29 June 1990 by ROSAT

Worked examples

Example 1 — a first encounter with ROSAT

Start with the simplest possible case. Write down what ROSAT 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 ROSAT 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 ROSAT 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 ROSAT

In research: ROSAT 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 ROSAT 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: ROSAT is common in secondary-school and first-year university syllabi. It links to neighbouring topics ROSAT objects, Satellites of Germany, Space telescopes, so understanding it makes those chapters shorter.
In everyday life: Look for ROSAT 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 ROSAT in 20 minutes

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

Frequently asked questions

What is ROSAT in simple terms?

Why does ROSAT 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 ROSAT?

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 ROSAT.