astronomy

TRACE

TRACE 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 TRACE rather than just read about it. In short: Transition Region and Coronal Explorer (TRACE, or Explorer 73, SMEX-4) was a NASA heliophysics and solar observatory designed to investigate the connections between fine-scale magnetic fields and the associated plasma structures on the Sun by providing high-resolution images and observation of the solar photosphere, the transition region, and the solar corona. A main focus of the TRACE instrument was the fine struct…

Key takeaways

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

Reference excerpt

Transition Region and Coronal Explorer (TRACE, or Explorer 73, SMEX-4) was a NASA heliophysics and solar observatory designed to investigate the connections between fine-scale magnetic fields and the associated plasma structures on the Sun by providing high-resolution images and observation of the solar photosphere, the transition region, and the solar corona. A main focus of the TRACE instrument was the fine structure of coronal loops low in the solar atmosphere. TRACE was the third spacecraft in the Small Explorer program, launched on 2 April 1998, and obtained its last science image on 21 June 2010, at 23:56 UTC. It reentered the atmosphere 600 km south of Perth, Australia on 18 July 2025, at 11:37 UTC.

Mission The Transition Region and Coronal Explorer (TRACE) was a NASA small explorer mission designed to examine the three-dimensional magnetic structures which emerge through the Sun's photosphere (the visible surface of the Sun) and define both the geometry and dynamics of the upper solar atmosphere (the transition region and corona). Its primary science objectives were to: (1) follow the evolution of magnetic field structures from the solar interior to the corona; (2) investigate the mechanisms of the heating of the outer solar atmosphere; and, (3) determine the triggers and onset of solar flares and mass ejections.

Spacecraft

The satellite was built by NASA's Goddard Space Flight Center. Its telescope was constructed by a consortium led by Lockheed Martin's Advanced Technology Center. The optics were designed and built to a state of the art surface finish by the Smithsonian Astrophysical Observatory (SAO). The telescope had a 30 cm (12 in) aperture and 1024 × 1024 charge-coupled device (CCD) detector giving an 8.5 arcminute field of view (FoV). The telescope was designed to take correlated images in a range of wavelengths from visible light through the Lyman alpha line to far ultraviolet. The different wavelength passbands corresponded to plasma emission temperatures from 4,000 to 4,000,000 K. The optics used a special multilayer technique to focus the difficult-to-reflect extreme ultraviolet (EUV) light; the technique was first used for solar imaging in the late 1980s and 1990s, notably by the MSSTA and NIXT sounding rocket payloads. TRACE was a single-instrument, three-axis stabilized spacecraft. The spacecraft attitude control system (ACS) utilized three magnetic-torquer coils, a digital Sun sensor, six coarse Sun sensors, a three-axis magnetometer, four reaction wheels, and three two-axis inertial gyros to maintain pointing. In science mode, the spacecraft used an instrument-provided guide telescope as a fine guidance sensor to provide a pointing accuracy of less than 5 arcseconds. Power was provided to the spacecraft through the use of four panels of gallium arsenide (GaAs) solar cells with a total area of 2 m2 (22 sq ft). The solar array actually produced power of around 220 watts, 85 W of which was used each orbit by the spacecraft and 35 W of which was used by the instrument each orbit. The remaining power was used for operational and decontamination heating of the spacecraft and telescope. A 9 A-hour nickel–cadmium battery (NiCd) provided energy during time when the spacecraft was in the Earth's shadow. Communications were provided via a 5 W S-band transponder, providing up to 2.25 Mbit/s downlink data transmission and 2 kbit/s uplink. Data were transmitted up to six times daily. Data were stored onboard using a solid-state recorder capable of holding up to 300 MB. The command and data handling system used a 32-bit 80386/80387 processor.

Experiment

TRACE Imaging Telescope The telescope was of Cassegrain design, 1.6 m (5 ft 3 in) long with an aperture of 30 cm (12 in). The focal length was 8.66 m (28.4 ft). The field of view of the telescope was 8.5 x 8.5 arcminutes with a spatial resolution of one arcsecond. The light was focused on a 1024 x 1024 element CCD detector (0.5 arcseconds/pixel). The temporal resolution of the instrument was less than 1 second, although the nominal temporal resolution was 5 seconds. Exposure times for observations ranged between 2 ms and 260 seconds. The primary and secondary mirrors had normal-incidence coatings specially designed for EUV and UV observations which divide the mirrors into quadrants. These segmented coatings were designed to provide identically sized and perfectly coaligned images. Which mirror quadrant was used for an observation was determined by the position of a quadrant selector shutter mechanism, positioned behind the entrance aperture. Three of the mirror coatings provided for observations in specific iron emission bands: Fe IX (central wavelength/bandwidth: 17.3 nm/0.64 nm); Fe XII (19.5 nm/0.65 nm); and Fe XV (28.4 nm/1.07 nm). The final mirror coating allowed broadband observations in the ultraviolet (centered on 500 nm). Further selection of observations in the UV could be made through the use of a filter wheel, mounted in front of the CCD. The filter wheel permitted continuum observations (170 nm/20 nm) as well as observations in emission bands for C (carbon) I and Fe II (160 nm/27.5 nm), C IV (155 nm/2 nm), and H (Hydrogen) I (Lyman-alpha) (121.6 nm/8.4 nm). The TRACE primary mirror assembly was based on primary mirror support assemblies used in SWATH, a small explorer developed for the U.S. Air Force, and NIXT, a set of rocket flights flown by the Smithsonian Astrophysical Observatory (SAO) five times between 1983 and 1993. Many of the designs and some of the space flight hardware from the MDI instrument on Solar and Heliospheric Observatory (SoHO) was also used.

Image gallery

Illustrations

Worked examples

Example 1 — a first encounter with TRACE

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

In research: TRACE 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 TRACE 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: TRACE is common in secondary-school and first-year university syllabi. It links to neighbouring topics Explorers Program, Missions to the Sun, Solar space observatories, so understanding it makes those chapters shorter.
In everyday life: Look for TRACE 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 TRACE in 20 minutes

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

Frequently asked questions

What is TRACE in simple terms?

Why does TRACE 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 TRACE?

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 TRACE.