astronomy

Segue 1

Segue 1 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 Segue 1 rather than just read about it. In short: Segue 1 is a dwarf spheroidal galaxy or globular cluster situated in the Leo constellation and discovered in 2006 by the Sloan Digital Sky Survey. It is located at a distance of about 23 kpc (about 75,000 light years) from the Sun and moves away from the Sun with a velocity of about 206 km/s.

Key takeaways

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

Reference excerpt

Segue 1 is a dwarf spheroidal galaxy or globular cluster situated in the Leo constellation and discovered in 2006 by the Sloan Digital Sky Survey. It is located at a distance of about 23 kpc (about 75,000 light years) from the Sun and moves away from the Sun with a velocity of about 206 km/s. Segue 1 has a noticeably elongated (ratio of axes ~ 2:1) shape with a half-light radius of about 30 pc. This elongation may be caused by tidal forces from the Milky Way galaxy if Segue 1 is being disrupted now. The name is due to the fact that it was found by the SEGUE program, the Sloan Extension for Galactic Understanding and Exploration.

Properties Segue 1 is one of the smallest and faintest satellites of the Milky Way—its integrated luminosity is about 300 times that of the Sun (absolute visible magnitude of about −1.5), which is much smaller than the luminosity of a typical globular cluster. Observations indicate its mass is about 600,000 solar masses, which means that Segue's 1 mass to light ratio is around 3400. Segue 1 had the highest known mass-to-light ratio of any observed galaxy as of 2011. A high mass to light ratio implies that Segue 1 may be dominated by dark matter. It is difficult, however, to estimate the mass of such faint objects due to significant foreground contamination, which inflates the velocity dispersion. In addition, any mass estimate is based on an implicit assumption that an object is gravitationally bound, which may not be true if it is being disrupted. The stellar population of Segue 1 consists mainly of old stars formed more than 12 billion years ago. The metallicity of these old stars is also very low at [Fe/H] ≈ −2.5 ± 0.8, which means that they contain 300 times less heavy elements than the Sun. Currently there is no star formation in Segue 1. Measurements have so far failed to detect neutral hydrogen in it—the upper limit is 13 solar masses. The object is estimated to contain 1000 stars. Of these, seven have been found to be in the red giant stage. The chemical composition of Segue 1 indicates no substantial chemical evolution has occurred since the galaxy formed, supporting the idea that it may be a surviving first galaxy that experienced only one burst of star formation, a fossil galaxy from the early universe. Segue 1 is located in the middle of the Sagittarius Stream and at approximately the same distance from the Sun. It may once have been a globular cluster of the Sagittarius Dwarf Elliptical Galaxy, which was later stripped from it by the tidal forces acting from the Milky Way galaxy. However, more recent studies concluded that Segue 1 is not actually associated with the Sagittarius stream and that it is not being tidally disrupted. If Segue 1 is a galaxy it may have been a satellite of the Sagittarius Dwarf Elliptical Galaxy in the past. In the work published in 2025 the authors claim that the stellar dynamics of Segue 1 are best modeled by a point-like mass in its center with mass of (4.5±1.5)×105 M☉ rather than dark matter. This point-like mass is interpreted as a supermassive black hole.

Notes

References

External links "Found:Heart of Darkness". W.M. Keck Observatory. Archived from the original on 10 March 2016. Retrieved 4 November 2011.

Worked examples

Example 1 — a first encounter with Segue 1

Start with the simplest possible case. Write down what Segue 1 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 Segue 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 Segue 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 Segue 1

In research: Segue 1 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 Segue 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: Segue 1 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 2006, Dwarf spheroidal galaxies, Globular clusters, so understanding it makes those chapters shorter.
In everyday life: Look for Segue 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.

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How to study Segue 1 in 20 minutes

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

Frequently asked questions

What is Segue 1 in simple terms?

Why does Segue 1 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 Segue 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 Segue 1.