science

HM 1

HM 1 is a science 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 HM 1 rather than just read about it. In short: HM 1, also known as Havlen-Moffat 1, is an open cluster located in the constellation of Scorpius, close to the galactic plane. It was first observed by R.

Key takeaways

HM 1 belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect HM 1 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of HM 1 from memory before moving on to harder problems.

Reference excerpt

HM 1, also known as Havlen-Moffat 1, is an open cluster located in the constellation of Scorpius, close to the galactic plane. It was first observed by R. J. Havlen and A. F. J. Moffat in 1976. HM 1 is thought to be 9,500 to 12,700 light-years (2,900 to 3,900 parsecs) away from the Earth, beyond the Carina–Sagittarius Arm. It is heavily reddened by interstellar extinction, so although it comprises mostly blue-colored stars, it appears brighter for longer-wavelength passbands. It is projected against the H II region known as RCW 121, and appears to be the source of ionization for the nearby regions RCW 122 and RCW 123.

Properties The extinction value for HM 1 is calculated to be EB−V = 1.85 magnitudes, and its distance was first estimated to be around 2.9 ± 0.4 kiloparsecs away. Later estimates put the cluster at around 3.3 kiloparsecs away; this is still one of the more closer massive star clusters. HM 1 is fairly young for an open cluster; it is estimated to be 1 to 2, or 2 to 4 million years old. This is indicated by the presence of Of stars, which have relatively short lives. However, a red supergiant with a bolometric magnitude of −6.6 and a mass of about 20 M☉ was discovered near the cluster, contradicting the supposed age of the cluster. However, subsequent work showed the star is likely in the foreground.

Composition HM 1 is noted for its components, including several Wolf–Rayet stars and Of stars. Both types of stars are fairly rare and very massive, and their coexistence in star clusters was unexpected. The evolution of Wolf–Rayet stars and Of stars in star clusters is currently unclear. Very few Wolf–Rayet stars have been found in star clusters, and a possible explanation is that the formation of these cluster Wolf–Rayet stars requires a binary star system containing two Of stars. Alternatively, cluster Wolf–Rayet stars may simply be rare because they represent a short stage in the evolution of Of stars, whether single or binary. Many of the stellar components are extremely blue-colored O-type stars that are among some of the most luminous stars known. Some of the candidate members listed have masses of over 20 M☉, making this cluster one of the richest known. Examples include the peculiar star LSS 4067, an O-type supergiant with a spectral type of O4If+. WR 89, another luminous star, is a strong X-ray source and is possibly a colliding-wind binary, based on data from XMM-Newton. In contrast, WR 87 has a high plasma temperature consistent with that of a colliding-wind binary but otherwise appears to be a single star (similar to WR 136).

Gallery

See also Cygnus OB2, an OB association containing many massive stars List of most massive stars

References

Notes

Illustrations

Worked examples

Example 1 — a first encounter with HM 1

Start with the simplest possible case. Write down what HM 1 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, 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 HM 1 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 HM 1 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 HM 1

In research: HM 1 appears in science 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 HM 1 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: HM 1 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Open clusters, Scorpius, so understanding it makes those chapters shorter.
In everyday life: Look for HM 1 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.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “HM 1” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study HM 1 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what HM 1 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 HM 1 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is HM 1 in simple terms?

HM 1, also known as Havlen-Moffat 1, is an open cluster located in the constellation of Scorpius, close to the galactic plane. It was first observed by R.

Why does HM 1 matter?

Because it connects several science 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 HM 1?

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 HM 1.