astronomy

SU Ursae Majoris

SU Ursae Majoris 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 SU Ursae Majoris rather than just read about it. In short: SU Ursae Majoris, or SU UMa, is a close binary star in the northern circumpolar constellation of Ursa Major. It is a periodic cataclysmic variable that varies in magnitude from a peak of 10.8 down to a base of 14.96.

Key takeaways

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

Reference excerpt

SU Ursae Majoris, or SU UMa, is a close binary star in the northern circumpolar constellation of Ursa Major. It is a periodic cataclysmic variable that varies in magnitude from a peak of 10.8 down to a base of 14.96. The distance to this system, as determined from its annual parallax shift of 4.53 mas, is 719 light-years. It is moving further from the Earth with a heliocentric radial velocity of +27 km/s. The variable nature of this star was discovered at the Moscow Observatory by Lidiya Tseraskaya (L. Ceraski) in 1908. It was classified as a U Geminorum-type variable, or dwarf nova. Observation since 1926 showed that this variable undergoes two different types of eruptions: a short maxima lasting around two days that ranged in brightness between 11.6–12.9 magnitude, and a longer maxima extending for 13 days that ranged between 10.4–11.8 magnitude. The later event came to be referred to as 'supermaxima' or 'superoutbursts'. Similar dwarf novae of this class have since been discovered, and SU UMa is now the prototype for this sub-category of variable stars. This is a single-lined spectroscopic binary with an orbital period of 1.83 hours. It consists of a white dwarf star that is acquiring matter from its close companion via an accretion disk. This disk is unstable and undergoes periodic outbursts which increase the luminosity of the system. For SU UMa, the accretion rate from the companion is 9.8×10−13 M☉·yr−1. X-ray emission has been detected in the vicinity of the white dwarf, which drops by a factor of four during outbursts. This emission is theorized to come from the boundary layer between the white dwarf and its accretion disk.

Illustrations

Worked examples

Example 1 — a first encounter with SU Ursae Majoris

Start with the simplest possible case. Write down what SU Ursae Majoris 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 SU Ursae Majoris 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 SU Ursae Majoris 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 SU Ursae Majoris

In research: SU Ursae Majoris 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 SU Ursae Majoris 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: SU Ursae Majoris is common in secondary-school and first-year university syllabi. It links to neighbouring topics Dwarf novae, Objects with variable star designations, Spectroscopic binaries, so understanding it makes those chapters shorter.
In everyday life: Look for SU Ursae Majoris 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 SU Ursae Majoris in 20 minutes

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

Frequently asked questions

What is SU Ursae Majoris in simple terms?

Why does SU Ursae Majoris 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 SU Ursae Majoris?

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 SU Ursae Majoris.