September

Key takeaways

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

Reference excerpt

September is the ninth month of the year in the Julian and Gregorian calendars. Its length is 30 days.

September in the Northern Hemisphere and March in the Southern Hemisphere are seasonally equivalent. In the Northern Hemisphere, the beginning of the meteorological autumn is on 1 September. In the Southern Hemisphere, the beginning of the meteorological spring is on 1 September. September marks the beginning of the ecclesiastical year in the Eastern Orthodox Church. It is the start of the academic year in many countries of the northern hemisphere, in which children go back to school after the summer break, sometimes on the first day of the month. Some Libras and Virgos are born in September, with Virgos being born on September 1st through September 22nd and Libras September 23rd through September 30. September (from Latin septem, "seven") was originally the seventh month in the oldest known Roman calendar, the calendar of Romulus c. 750 BC, with March (Latin Martius) being the first month of the year until perhaps as late as 451 BC. After the calendar reform that added January and February to the beginning of the year, September became the ninth month but retained its name. It had 29 days until the Julian reform, which added a day.

Events Ancient Roman observances for September include Ludi Romani, originally celebrated from September 12 to September 14, later extended to September 5 to September 19. In the 1st century BC, an extra day was added in honor of the deified Julius Caesar on 4 September. Epulum Jovis was held on September 13. Ludi Triumphales was held from September 18–22. The Septimontium was celebrated in September, and on December 11 on later calendars. These dates do not correspond to the modern Gregorian calendar. September was called the "harvest month" in Charlemagne's calendar. September corresponds partly to the Fructidor and partly to the Vendémiaire of the first French republic. September is called Herbstmonat, harvest month, in Switzerland. The Anglo-Saxons called the month Gerstmonath, barley month, that crop being then usually harvested. In 1752, the British Empire adopted the Gregorian calendar. In the British Empire that year, September 2 was immediately followed by September 14. On Usenet, it is said that September 1993 (Eternal September) never ended. In the United States, September is one of the most common birth months (third most popular after August and July, which both have 31 days), as all but one Top 10 most common birthdays are in September, based on the National Center for Health Statistics statistics on births between 1994 and 2014. The most common birthday is September 9 (#1), least common is September 1 (#250).

Astronomy and astrology The September equinox takes place in this month, and certain observances are organized around it. It is the Autumn equinox in the Northern Hemisphere, and the Vernal equinox in the Southern Hemisphere. The dates can vary from 21 September to 24 September (in UTC). September is mostly in the sixth month of the astrological calendar (and the first part of the seventh), which begins at the end of March/Mars/Aries.

Symbols September's birthstone is the sapphire. The birth flowers are the forget-me-not, morning glory and aster. The zodiac signs are Virgo (until September 22) and Libra (September 23 onward).

Observances This list does not necessarily imply either official status or general observance.

Non-Gregorian List of observances set by the Bahá'í calendar List of observances set by the Chinese calendar List of observances set by the Hebrew calendar List of observances set by the Islamic calendar List of observances set by the Solar Hijri calendar

Month-long Amerindian Heritage Month (Guyana) Childhood Cancer Awareness Month (United Kingdom) Gynecologic Cancer Awareness Month Leukemia and Lymphoma Awareness Month Ovarian Cancer Awareness Month Thyroid Cancer Awareness Month National Suicide Prevention Month Vegetable Month

United States Better Breakfast Month Food Safety Education Month National Childhood Obesity Awareness Month Hydrocephalus Awareness Month Pain Awareness Month National Preparedness Month National Prostate Health Month National Sickle Cell Awareness Month National Yoga Month

Food months National Bourbon Heritage Month California Wine Month National Chicken Month National Honey Month National Mushroom Month National Italian Cheese Month National Papaya Month National Potato Month National Rice Month National Whole Grains Month National Wild Rice Month

Movable Gregorian

Engineering Day (Egypt) White Balloon Day Day of the Programmer Te Wiki o te Reo Māori (Māori Language Week) (New Zealand) See also Movable Western Christian observances See also Movable Eastern Christian observances

First Wednesday Administrative Professionals' Day (South Africa)

First Thursday Engineer's Days (Tanzania)

First Friday Engineer's Days (Tanzania) Labor Day (Marshall Islands) Teachers' Day (Singapore)

First Sunday Brazilian Day (International observance) Father's Day (Australia, Fiji, New Zealand, Papua New Guinea) Memorial of the Holy Guardian Angels (Roman Catholic Church, October 2 in most locations, first Sunday in September by special dispensation)

First Sunday after September 4 Wakes Week (Parts of England and Scotland) Abbots Bromley Horn Dance (Abbots Bromley, Staffordshire, England)

Week of the first Monday National Payroll Week (United States, Canada, United Kingdom)

Week of September 10 National Suicide Prevention Week (United States)

First Monday Labour Day (Canada, Palau, United States)

Nearest weekday to September 12 Saragarhi Day (Sikhism)

Second Saturday Day of the Workers in the Oil, Gas, Power, and Geological Industry (Turkmenistan)

Saturday after first Monday Carl Garner Federal Lands Cleanup Day (United States)

Second Sunday Auditor's Day (Church of Scientology) Father's Day (Latvia) National Grandparents' Day (Canada, Estonia, Philippines) Tanker's Day (Russia) Turkmen Bakhshi Day (Turkmenistan) International Crane Day

First Sunday after first Monday National Grandparents' Day (United States)

Week of September 17 Celebrate Freedom Week (Kansas and Texas, United States)

Third Tuesday Prinsjesdag (Netherlands)

September 17 but observed on previous Friday if it falls on a Saturday or following Monday if on a Sunday Constitution Day and Citizenship Day (United States)

Third Friday National POW/MIA Recognition Day (United States)

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with September

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

In research: September 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 September 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: September is common in secondary-school and first-year university syllabi. It links to neighbouring topics Months, September, so understanding it makes those chapters shorter.
In everyday life: Look for September 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.

How to study September in 20 minutes

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

Frequently asked questions

What is September in simple terms?

September is the ninth month of the year in the Julian and Gregorian calendars. Its length is 30 days.

Why does September 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 September?

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 September.