astronomy

Tau Canis Majoris

Tau Canis 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 Tau Canis Majoris rather than just read about it. In short: Tau Canis Majoris is a multiple star system in the constellation Canis Major, consisting of five stars. Its name is a Bayer designation that is Latinized from τ Canis Majoris, and abbreviated Tau CMa or τ CMa.

Key takeaways

Tau Canis 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 Tau Canis Majoris to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Tau Canis Majoris from memory before moving on to harder problems.

Reference excerpt

Tau Canis Majoris is a multiple star system in the constellation Canis Major, consisting of five stars. Its name is a Bayer designation that is Latinized from τ Canis Majoris, and abbreviated Tau CMa or τ CMa. This system is approximately 5,000 light years distant from Earth and is the brightest member of the open cluster NGC 2362. This star is sometimes known as the 'Mexican Jumping Star' by amateur astronomers, because it can appear to 'jump around' with respect to the other stars in the cluster because of its marked contrast in brightness.

System

τ Canis Majoris lies at the center of the very young open cluster NGC 2362, which contains several hundred stars. It is by far the brightest member of the cluster and none of the other members have evolved away from the main sequence. A number of stars were catalogued by John Herschel as companions of the primary, τ CMa A: component B is a 10th magnitude star 8.6 arc-seconds distant; component C is a 14th magnitude star 14.2 arc-seconds away; and component D is an 8th magnitude star at 85 arc-seconds. These stars are all thought to be main sequence members of NGC 2362. A period of 94,000 years has been suggested for the AB pair assuming they are gravitationally bound. In 1951, component A was resolved into a double separated by only 0.15". The companion is an O-type bright giant with an orbital period between 300 and 400 years and a mass estimated at 25 times that of the Sun. The Washington Double Star Catalog lists the pair as magnitude 4.89 Aa and magnitude 5.33 Ab, but the CCDM designates the components as A and P. Component E was discovered in 2010; it is less than 1" away from the 4.89 magnitude main component and is 9th magnitude.

The primary component A is itself a spectroscopic binary with a period of 154.9 days. Its variable radial velocity was discovered in 1906 and the first orbital elements published in 1928. More recently, Hipparcos satellite data revealed the existence of a 1.282 day eclipsing binary within the system, with two equal minima where the brightness dips by half a magnitude. The eclipsing binary was later revealed to be the secondary component, Aa2, with its subcomponents being named Aa2a and Aa2b. The spectrum and luminosity are dominated by component Aa which is now considered to be an O8.5 supergiant. It is thought to have a mass around 30 solar masses, a radius 17.7 times that of the Sun, temperature of 32,500 K, and a luminosity 280,000 times that of the Sun. The two eclipsing stars are almost identical, rapidly-rotating B-type stars, with masses of 19 solar masses. They are so close to each other that they share a common envelope, systems with such a characteristic are called overcontact binaries. The properties of the minor components of the τ CMa grouping are poorly known. Spectral types of B2Vn, B5Vnn, B0.7V and B2: V have been assigned to the components B, C, D and E, respectively. UW Canis Majoris is another 4th magnitude star less than half a degree away, and is itself an eclipsing binary system associated with NGC 2362. It has been catalogued as τ2 CMa, but that name is now rarely used.

References

External links The Mexican Jumping Star

Illustrations

Worked examples

Example 1 — a first encounter with Tau Canis Majoris

Start with the simplest possible case. Write down what Tau Canis 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 Tau Canis 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 Tau Canis 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 Tau Canis Majoris

In research: Tau Canis 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 Tau Canis 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: Tau Canis Majoris is common in secondary-school and first-year university syllabi. It links to neighbouring topics B-type main-sequence stars, Bayer objects, Beta Lyrae variables, so understanding it makes those chapters shorter.
In everyday life: Look for Tau Canis 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 Tau Canis Majoris in 20 minutes

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

Frequently asked questions

What is Tau Canis Majoris in simple terms?

Why does Tau Canis 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 Tau Canis 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 Tau Canis Majoris.