# Season cycle < Year?

Is it possible for a planet's axis to precess or wobble in such a way that its season cycle is of lesser duration than its year? The gyroscopic precession will thus give seasons to one or the other hemisphere during a possibly hundreds-year-long revolution around its star. Earth's precession is very much longer than it's revolution period, but is it possible that these could be reversed and a planet still be habitable?

Is it possible for a planet's axis to precess or wobble in such a way that its season cycle is of lesser duration than its year?

For this, definitely yes, if you tweak some parameters. On the Wikipedia page for Axial Precision, you'll find the set of equations and parameters that allow you to calculate the precessional rate for Earth's axis. Mainly, the Earth's precession is caused by a variety of factors but primarily due to the Moon and Sun (and thus related orbital/body parameters). If you look at those equations, and start tweaking values in them, you'll find you can force the axial precession period to be less than a "year". I'll go through and construct just such a system.

First though, I need to figure out the orbital parameters of the planet such that it has a 100-year long revolution period. This is acheived by using Kepler's Third Law, relating orbital period, orbital distance, and mass of the Sun (and Earth, but that's negligible). The relevant form of the equation, for our purposes is:

$$P^2 = frac{a^3}{M_{mathrm{Sun}}}$$

where, $P$ is the orbital period in years, $a$ is the orbital distance in AU (1 AU is the distance between Earth and the Sun), and $M_{mathrm{Sun}}$ is the mass of the Sun in units of solar masses. If you're dictating that $P=100 mathrm{years}$, then I find I can set $a = 10 mathrm{AU}$ and $M_{mathrm{star}} = 0.1 M_{odot}$ and make this equation true. What that means is that this new planet orbits a star which is 10 times less massive than our own star (making it a red dwarf) and orbits 10 times farther than Earth. My choice of parameters is all serendipitous and you could certainly find other parameters that work as well.

Now, given those parameters above, we can try to calculate the precessional rate for this new planet. I'll assume this new planet has an orbiting moon, just like Earth does. The two important equations for calculating the Earth's precessional rate are to account for the contributions from the Sun and the Moon. The equations are given by:

$$P_{mathrm{Sun}} = frac{3}{2}left(frac{GM_{mathrm{Sun}}}{a_{mathrm{Earth}}(1-e_{mathrm{Earth}})^{3/2}} ight)left(frac{(C-A)}{C}frac{cos epsilon}{omega} ight)$$

$$P_{mathrm{Moon}} = frac{3}{2}left(frac{GM_{mathrm{Moon}}(1-1.5sin^2 i_{mathrm{Moon}})}{a_{mathrm{Moon}}(1-e_{mathrm{Moon}})^{3/2}} ight)left(frac{(C-A)}{C}frac{cos epsilon}{omega} ight)$$

In these equations, $G$ is the Gravitational Constant, $M$ is mass in kg, $a$ is the orbital distance in meters, $e$ is the orbital eccentricity, $i$ is the inclination of the Moon's orbital plane wrt to the ecliptic, $(C-A)/C = 0.003273763$ is a measurement of the Earth's shape, $epsilon$ is the Earth's axis' angle, nominally $23.43928^mathrm{o}$, and finally $omega$ is the rotation rate in rad/s.

Plugging in all the values for the Earth-Moon-Sun system (which you can find on the wiki page), you find that $P_{mathrm{Sun}} + P_{mathrm{Moon}} = 7.789 imes 10^{-12} mathrm{rad/s}$ and to convert to a time scale, you can multiply by $2 imes10^{-7}$. Doing so gives you the nominal Earth precessional period of about 26,000 years.

Given all of that, we can start playing with parameters to get it such that the precessional period for our new system is less than 100 years. I already said that $a_{mathrm{Earth}}$ is 10 times larger and that $M_{mathrm{Sun}}$ is 10 times smaller so we could get the period of 100 years. I found that I could make the following additional changes.

• The moon is now 5.8 times more massive than our Moon.
• The moon is now a quarter of the distance of our Moon.
• The planet is spinning twice as fast.

With those changes, I find that the precessional period falls down to about 50 years, or half an orbit. You can continue to play with the numbers to get a different result.

An important consideration here is whether or not such a system is likely to even form. I think, given the system I've created, it is not outside the realm of possibilities. To have such a large, almost binary planetary system be so far away from a small star is unlikely, but I don't think impossible. The real difficulty here is that you've set the orbital period to such a long timescale. If you were to relax that a bit to something much shorter (say 10 years) you'd get a more realistic (and likely habitable) system.

Earth's precession is very much longer than it's revolution period, but is it possible that these could be reversed and a planet still be habitable?

Certainly there's nothing to say a planet with a precessional period shorter than the revolution period is uninhabitable. What will make it uninhabitable is being too far from the star. The extreme orbital time you've provided necessitated having a planet that is likely too far from the star to be in the "habitable zone". You just have to play with all the parameters and find something that fits all your needs.

Another thing to consider is that if a planet has such a large and close moon as I've constructed, it will likely cause the planet to slow its rotation rate over short (astronomical) timescales. The planets rotation rate has a significant affect on the precessional rate and slowing it down over short timescales may mean your system doesn't keep the precessional rate under the rotation period for too long.

## Minor lunar standstill and Harvest Moon

Every year at this time, we in the Northern Hemisphere have our full Harvest Moon, the full moon closest to the autumn equinox. In 2016, the full Harvest Moon comes on September 16 at 1905 UTC. The Harvest Moon phenomenon consists of the moon looking nearly or entirely full, and rising close to the time of sunset, for several evenings in a row. That’s unlike most full moons, which rise on average about 50 minutes later each night. In 2016, though, the yearly phenomenon of the Harvest Moon will be somewhat less grand than usual due to what is called a minor lunar standstill. It’s all about the inclination of the moon’s orbit to the plane of the Earth’s equator, which determines when and where on the horizon we see the moonrise. Follow the links below to learn more:

Lunar standstill calendar at the National Museum of the American Indian at Washington D.C. Image via Flickr user catface3.

Inclination of moon’s orbit to Earth’s equator. Unlike Earth’s moon, many moons in the solar system orbit above the equator of their respective planets. If our moon did likewise – orbited around the Earth’s equator – then the moon would rise due east and set due west every day. Our moon’s orbit is inclined to the plane of Earth’s equator, however. Our moon orbits Earth on nearly the same plane that Earth orbits the sun (aka the plane of the ecliptic).

That’s why, as it rises and sets each day, Earth’s moon spends about two weeks rising and setting south of due east and west, and then two weeks rising and setting north of due east and west.

This inclination of the moon’s orbit also creates the grand parade of moonlit nights, the moon rising close to the time of sunset – the Harvest Moon phenomenon – we mentioned earlier.

Typically, for several nights around the Harvest Moon, there will be bright moons ascending in the east, around the time of dusk. It’s as though, in the month of the Harvest Moon, we have a full moon for several nights in a row.

But this year that effect is diminished, because this year is only one year after the minor standstill year of 2015, when the moon swung minimally south and north of the celestial equator in its 18.6-year standstill cycle. When the moon reached its southern standstill – farthest south – on September 21, 2015, it was only be 18.134 o south of the equator. One fortnight later, when the moon swung to its northern standstill – farthest north – it was only 18.140 o north of the equator on October 3, 2015.

This year won’t be much different, as the moon swings from 18.451 o south to 18.475 o north of the celestial equator during the fortnight period between September 10 to September 23, 2016.

Midway between the southern standstill on September 10, 2016, and the northern standstill on September 23, 2016, the Northern Hemisphere will have its full Harvest Moon on September 16, 2016. The moon is going eastward in its orbit – as well as northward. Each day, the moon rises farther north along the eastern horizon, and that’s what is responsible for the full Harvest Moon phenomenon in the Northern Hemisphere. When the moon rises farther north of where it did the day before, the moon also rises sooner than the average 50 minutes later daily.

But this year, in 2016, the northward movement of the moonrises along the eastern horizon is not as great as it could be, due to the minor lunar standstill. The several nights of dusk-till-dawn moonlight that you’d normally expect from the Harvest Moon are not as pervasive as in other years.

To recap: The September 2016 full Harvest Moon occurs when the moon’s orbital inclination to the equator is at a near minimum in the moon’s 18.6-year standstill cycle. The shallower inclination of the moon’s orbital plane, relative to the plane of the Earth’s equator, reduces the impact of the Harvest Moon in 2016. See 18.6-year lunar cycle impacts Harvest Moon, below, for a fuller explanation.

The table below helps to illustrate moonrise times for Fairbanks, Alaska. The azimuth reads 90 o when the moon is rising due east, more than 90 o when rising south of due east and less than 90 o when rising north of due east.

Fairbanks, Alaska (65 o north latitude)

2016 Full Harvest Moon: September 16

18.6-year lunar cycle impacts Harvest Moon. The inclination of the moon’s orbital path to the plane of the Earth’s equator changes over a cycle of 18.6 years. For instance, in the year 2006 – and again in the year 2025 – the moon in its monthly travels swings from about 28.5 o south to 28.5 o north of the Earth’s equator. Sometimes this extreme inclination is called a major lunar standstill. The greater inclination of the moon’s orbit accentuates the effect of the Harvest Moon.

Throughout the year 2016, in contrast, the moon’s monthly travels take the moon from roughly 18.5 o south to 18.5 o north of the Earth’s equator. This shallow inclination of the moon’s orbit to the celestial equator acts to lessen the effect of the Harvest Moon.

So we’re only one year past the minor lunar standstill year in 2015. Therefore, the diminished inclination of the moon’s orbit to the equator lessens the impact of this year’s 2016 Harvest Moon. In fact, the next major lunar standstill year won’t be forthcoming until 2025. (See table at the bottom of this post.)

The plane of the moon’s orbit is inclined at 5 o to the ecliptic (plane of the Earth’s orbit). In a year when the moon’s orbit intersects the ecliptic at the March equinox point, going from north to south, we have a minor lunar standstill year. Thereby, the lunar standstill points are 5 o closer to the equator than are the solstice points (23.5 o – 5 o = 18.5 o declination).

What is a Harvest Moon? The full moon occurring most closely to the autumnal equinox (the Northern Hemisphere’s September equinox/Southern Hemisphere’s March equinox) enjoys the designation of Harvest Moon. The full Harvest Moon will come on September 16, 2016, in the Northern Hemisphere – and to the Southern Hemisphere on March 12, 2017.

There is no Harvest Moon at the equator and not enough of one to say so in the tropical regions of the globe. You really have to be well north (or south) of the tropics to observe the year’s grandest parade of moonlit nights around the time of the autumn equinox. The farther north or south of the Earth’s equator that you live, the longer the procession of moonlit nights accompanying the harvest season.

The term Harvest Moon might be of European origin, because northern Europe is much closer to the Arctic than the tropics. Before the advent of artificial lighting, people planned nocturnal activity around the moon, knowing the moon provides dusk-till-dawn moonlight on the night of the full moon. But farmers of old were also aware that the Harvest Moon – the closest full moon to the autumn equinox – could be relied upon to provide dusk-till-dawn moonlit for several days in a row at mid-temperate latitudes, or even as long as a week straight at far-northern latitudes.

This bonanza of moonlight in the season of waning daylight remains the legacy of the Harvest Moon.

Beautiful twilight photo a Harvest Moon by Amy Simpson-Wynne in Virginia.

Some peculiarities of the Harvest Moonrise In the Northern Hemisphere, the moon rises farther north along the horizon each evening for a number of days following the appearance of the full Harvest Moon. This northward movement along the horizon reduces the lag time between successive moonrises, so the moon rises at or near the time of sunset for several days in succession.

In the Southern Hemisphere, by the way, the full Harvest Moon will occur in March 2017, as the moon is moving maximally southward from night to night.

In fact, it’s even possible – in or near a major standstill year – for the moon to rise at an earlier time than on the previous day at high northern (or southern) latitudes. For a prime example, see the chart below for Anchorage, Alaska, noting the moonrise times in September 2025, a major lunar standstill year.

Also, note the moonrise times for September 2016 in Anchorage, Alaska, during the year of the minor lunar standstill. Obviously, the minor lunar standstill lessens the impact of the Harvest Moon.

Seattle, Washington (48 o north latitude)

2016 Full Harvest Moon: September 16 * 2025 Full Harvest Moon: September 7

 Date in 2016 Moonrise Sunset Date in 2025 Moonrise Sunset September 16 7:31 p.m. 7:20 p.m. September 7 7:42 p.m. 7:39 p.m. September 17 8:04 p.m. 7:18 p.m. September 8 7:59 p.m. 7:37 p.m. September 18 8:37 p.m. 7:16 p.m. September 9 8:17 p.m. 7:35 p.m. September 19 9:18 p.m. 7:14 p.m. September 10 8:38 p.m. 7:33 p.m.

Anchorage, Alaska (61 o north latitude)

2016 Full Harvest Moon: September 16 * 2025 Full Harvest Moon: September 7

Harvest Moon by Annie Lewis in Spain.

Bottom line: The diminished inclination of the moon’s orbit to Earth’s equator shortens the procession of moonlit nights accompanying this year’s Harvest Moon.

## Season

A season is a period of the year that is distinguished by special climate conditions. The four seasons—spring, summer, fall, and winter—follow one another regularly. Each has its own light, temperature, and weather patterns that repeat yearly.

In the Northern Hemisphere, winter generally begins on December 21 or 22. This is the winter solstice, the day of the year with the shortest period of daylight. Summer begins on June 20 or 21, the summer solstice, which has the most daylight of any day in the year. Spring and fall, or autumn, begin on equinoxes, days that have equal amounts of daylight and darkness. The vernal, or spring, equinox falls on March 20 or 21, and the autumnal equinox is on September 22 or 23.

The seasons in the Northern Hemisphere are the opposite of those in the Southern Hemisphere. This means that in Argentina and Australia, winter begins in June. The winter solstice in the Southern Hemisphere is June 20 or 21, while the summer solstice, the longest day of the year, is December 21 or 22.

Seasons occur because Earth is tilted on its axis relative to the orbital plane, the invisible, flat disc where most objects in the solar system orbit the sun. Earth’s axis is an invisible line that runs through its center, from pole to pole. Earth rotates around its axis.

In June, when the Northern Hemisphere is tilted toward the sun, the sun’s rays hit it for a greater part of the day than in winter. This means it gets more hours of daylight. In December, when the Northern Hemisphere is tilted away from the sun, with fewer hours of daylight.

Seasons have an enormous influence on vegetation and plant growth. Winter typically has cold weather, little daylight, and limited plant growth. In spring, plants sprout, tree leaves unfurl, and flowers blossom. Summer is the warmest time of the year and has the most daylight, so plants grow quickly. In autumn, temperatures drop, and many trees lose their leaves.

The four-season year is typical only in the mid-latitudes. The mid-latitudes are places that are neither near the poles nor near the Equator. The farther north you go, the bigger the differences in the seasons. Helsinki, Finland, sees 18.5 hours of daylight in the middle of June. In mid-December, however, it is light for less than 6 hours. Athens, Greece, in southern Europe, has a smaller variation. It has 14.5 hours of daylight in June and 9.5 hours in December.

Places near the Equator experience little seasonal variation. They have about the same amount of daylight and darkness throughout the year. These places remain warm year-round. Near the Equator, regions typically have alternating rainy and dry seasons.

Polar regions experience seasonal variation, although they are generally colder than other places on Earth. Near the poles, the amount of daylight changes dramatically between summer and winter. In Barrow, Alaska, the northernmost city in the U.S., it stays light all day long between mid-May and early August. The city is in total darkness between mid-November and January.

Illustration by Mary Crooks

Sometimes, seasons are determined by both natural and man-made activity. In the U.S. state of Alaska, people like to say there are three seasons: "winter, still winter, and construction season."

Ritu
A ritu is a season in the traditional Hindu calendar, used in parts of India. There are six ritu: vasanta (spring) grishma (summer) varsha (rainy or monsoon) sharat (autumn) hemant (pre-winter) and shishira (winter).

'Tis the Season
The word 'season' can be used to signify a time of year when an activity or process is allowed to happen. Seasons can be natural, like hurricane season, which is the time of year when hurricanes are most likely to develop. Seasons can also be artificially created, like hunting season, which is the time of year a community allows people to hunt certain wild animals.

Meteorological Seasons
Meteorologists, scientists who study the weather, divide each of the seasons into three whole months. Spring begins March 1, summer June 1, autumn September 1, and winter December 1.

## Earth and the sun

The cycle of seasons is caused by Earth's tilt toward the sun. The planet rotates around an (invisible) axis. At different times during the year, the northern or southern axis is closer to the sun. During these times, the hemisphere tipped toward the star experiences summer, while the hemisphere tilted away from the sun experiences winter, according to the National Oceanic and Atmospheric Administration (NOAA).

At other locations in Earth's annual journey, the axis is not tilted toward or away from the sun. During these times of the year, the hemispheres experience spring and autumn.

The astronomical definition of the seasons relates to specific points in Earth's trip around the sun. The summer and winter solstice, the longest and shortest day of the year, occur when Earth's axis is either closest or farthest from the sun. The summer solstice in the Northern Hemisphere occurs around June 21, the same day as the winter solstice in the Southern Hemisphere, according to NOAA. The south's summer solstice occurs around December 21, the winter solstice for the north. In both hemispheres, the summer solstice marks the first day of astronomical summer, while the winter solstice is considered the first day of astronomical winter.

Equinoxes are another significant day during Earth's journey around the Sun. On these days, the planet's axis is pointed parallel to the Sun, rather than toward or away from it. Day and night during the equinoxes are supposed to be close to equal. The spring, or vernal, equinox for the northern hemisphere takes place around March 20, the same day as the south's autumnal equinox. The vernal equinox in the southern hemisphere occurs around September 20, when people in the north celebrate the autumnal equinox. The vernal equinox marks the first day of astronomical spring for a hemisphere, while the autumnal equinox ushers in the first day of fall. [Infographic: Earth's Solstices & Equinoxes Explained]

But changes in the weather often precede these significant points. The meteorological seasons focus on these changes, fitting the seasons to the three months that best usher them in. December to February marks meteorological winter in the Northern Hemisphere and meteorological summer in the southern. March, April, and May are lauded as spring or autumn, depending on the location, while June through August are the months of summer for the north and winter for the south. September, October, and November conclude the cycle, ushering in fall in northern regions and spring in southern, according to NOAA.

The seasons can bring a wide variety to the year for those locations that experience them in full. The weather in each one may allow people to engage in activities that they cannot perform in others — skiing in the winter, swimming in the summer. Each season brings with it its own potential dangers, but also its own particular brand of beauty.

## Facts On Earth’s Orbit, Seasons & Cycles ⧂

Earth is speeding around the Sun at over 107,000 kilometres an hour and swings closest to the Sun around Christmas time, but you’d never know it! Its axial tilt causes the seasons to come and go and the long-term axial wobbles (and other changes in its orbit) results in Earth’s 100,000 year Ice Age cycles! You can enjoy reading and learn all about it here!

### Interesting Facts About The Earth’s Orbit, Seasons & Cycles!

For the majority of human history (until a few hundred years ago) Earth was believed to be the centre of the universe and everything orbited around it! In fact, Earth is really only the 3 rd planet from the Sun which everything in the solar system ultimately orbits around.

• Earth orbits at an average distance of 149.6 million kilometres from the Sun, in an area of space scientists often refer to as ‘the habitable zone’. This means that Earth orbits near the middle of a zone which receives just enough energy from the Sun to keep surface water in a liquid state. Like the story of Goldilocks and the Three Bears, the Planet Venus is too close to the Sun (so is too hot) and Jupiter is too far (so is too cold), but Earth is just right!
• No orbit is a perfect circle and Earth’s orbit around the Sun is no different. On January 4 th each year, the Earth is slightly closer to the Sun (known as perihelion) with a distance of 147.1 million km (91.4 million miles). Six months later during the first week of July, Earth is further away from the Sun at a distance of 152.1 million km (94.5 million miles).
• The slight difference in distance from the Sun means the southern hemisphere receives 6.9% more sunlight energy during its summer than summers in the northern hemisphere when the Earth is further from the Sun!
• Despite what you may have heard, Earth’s seasons aren’t caused by Earth’s distance from the Sun! The seasons are caused by the tilt of the Earths rotational axis - that imaginary line through each of the poles which Earth rotates around!
• Currently, the Earth is rotating at an angle of 23.4° relative to its orbit of the Sun.
• This ‘axial tilt’ causes one hemisphere to be pointed more towards the Sun at certain times of the year. This means that for half a year one hemisphere experiences longer days than the other so is warmer because of the extra sunlight! This results in the seasons alternating between summer and winter every year as the Earth orbits the Sun.
• If the Earth rotated straight up and down, as it orbited the Sun, we’d have no seasons!

### Long-Term Earth Cycles

Earth’s orbital characteristics aren’t fixed over long periods of time (Learn about orbits). Over thousands of years Earth’s orbital shape, axial tilt and the direction the axis is pointing changes. This leads to slight variations in the amount of energy areas of the Earth’s surface receives.

A very clever scientist named Milutin Milankovitch calculated the way these cycles change over time and how they are related to variations in Earth’s climate. These three changes in Earth’s orbital characteristics (known as the Milankovitch Cycles) cause the formation of the long-term 100,000 years Ice Ages cycles!

The shape of Earth’s orbit changes from almost circular to mildly elliptical (oval-shaped) over the course of

These changes to Earth’s orbit and rotational axis are caused by the gravitational influences of the Sun, Moon, Jupiter, Saturn and their tidal forces. But don’t worry we’re currently in a ‘warm’ period of the climate cycle so another ice age isn’t expected for over 50,000 years!

## Season cycle < Year? - Astronomy

The Earth's axis is tilted from perpendicular to the plane of the ecliptic by 23.45°. This tilting is what gives us the four seasons of the year - spring, summer, autumn (fall) and winter. Since the axis is tilted, different parts of the globe are oriented towards the Sun at different times of the year.

Summer is warmer than winter (in each hemisphere) because the Sun's rays hit the Earth at a more direct angle during summer than during winter and also because the days are much longer than the nights during the summer. During the winter, the Sun's rays hit the Earth at an extreme angle, and the days are very short. These effects are due to the tilt of the Earth's axis.

Solstices
The solstices are days when the Sun reaches its farthest northern and southern declinations. The winter solstice occurs on December 21 or 22 and marks the beginning of winter (this is the shortest day of the year). The summer solstice occurs on June 21 and marks the beginning of summer (this is the longest day of the year).

Equinoxes
Equinoxes are days in which day and night are of equal duration. The two yearly equinoxes occur when the Sun crosses the celestial equator.

The vernal equinox occurs in late March (this is the beginning of spring in the Northern Hemisphere and the beginning of fall in the Southern Hemisphere) the autumnal equinox occurs in late September (this is the beginning of fall in the Northern Hemisphere and the beginning of spring in the Southern Hemisphere).

## The Astronomical Seasons

People have used observable periodic natural phenomena to mark time for thousands of years. The natural rotation of Earth around the sun forms the basis for the astronomical calendar, in which we define seasons with two solstices and two equinoxes . Earth’s tilt and the sun’s alignment over the equator determine both the solstices and equinoxes.

The equinoxes mark the times when the sun passes directly above the equator. In the Northern Hemisphere, the summer solstice falls on or around June 21, the winter solstice on or around December 22, the vernal or spring equinox on or around March 21, and the autumnal equinox on or around September 22. These seasons are reversed but begin on the same dates in the Southern Hemisphere.

Because Earth actually travels around the sun in 365.24 days, an extra day is needed every fourth year, creating what we know as Leap Year. This also causes the exact date of the solstices and equinoxes to vary. Additionally, the elliptical shape of Earth’s orbit around the sun causes the lengths of the astronomical seasons to vary between 89 and 93 days. These variations in season length and season start would make it very difficult to consistently compare climatological statistics for a particular season from one year to the next. Thus, the meteorological seasons were born.

## Table 4: Summary of Solar Eclipses in Saros Series -13 to 190

The number of eclipses in each series is listed followed by the calendar dates of the first and last eclipses in the Saros. Finally, the chronological sequence of eclipse types in the series is tabulated. The number and type of eclipses varies from one Saros series to the next as reflected in the sequence diversity. Note that the tables make no distinction between central and non-central umbral/antumbral eclipses. The following abbreviations are used in the eclipse sequences:

The Catalog of Solar Eclipse Saros Series contains links to 181 web pages, each one listing the details of all eclipses in a particular Saros series:

## Classroom activity - Humanities and Social Sciences (HASS) Year 5

In this classroom activity students will create a seasonal resource calendar based on observing and researching the life cycles of local flora and fauna, and then relate these cycles to the annual appearance of seasonal stars.

### Curriculum connections

#### This resource addresses the following content description from the Australian Curriculum:

• Types of resources (natural, human, capital) and the ways societies use them to satisfy the needs and wants of present and future generations (ACHASSK120)

#### This resource addresses the following excerpts from the achievement standard for Year 5 in Humanities and Social Sciences (HASS):

• identify and describe the interconnections between people and the human and environmental characteristics of places, and between components of environments
• identify the effects of these interconnections on the characteristics of places and environments
• recognise that choices need to be made when allocating resources
• develop questions for an investigation
• locate and collect data and information from a range of sources to answer inquiry questions
• interpret data to identify and describe distributions, simple patterns and trends, and to infer relationships, and suggest conclusions based on evidence

### Activity &ndash Examining seasonal calendars

Suggested timing: 30-45 minute activity and discussion

Required resources: Computer, internet access, printed or online copy CSIRO Indigenous seasons calendars 10

1. Go to the CSIRO Indigenous Seasons Calendars website and view the different calendars available online.
2. Students should compare calendars from two or more regions and discuss the below questions as a class:
1. What do these calendars focus on in relation to community needs? Food, water, weather?
2. How do these calendars help the people live sustainably?
3. How are these resources linked to Aboriginal and Torres Strait Islander Peoples' connection to the land?
4. Do these calendars feature an astronomical component? If not, why?
1. The first is the Coalsack nebula, which is a dark space in the Milky Way next to the Southern Cross (they can read about it online). When is it visible in the dawn sky from Bathurst and Melville Islands (Tiwi country)? (They can use Stellarium to examine this).
1. Teacher note: it is only visible during the wet season from November to March. Therefore, that would be a useful indicator of that season, which is noted in Tiwi traditions. 11 In Tiwi traditions, a group of star-women make their camp within the Coalsack. Since it is only visible during the wet season, they do not have any camp fires. It&rsquos also the reason the Coalsack doesn&rsquot appear to have any stars in it.
1. Teacher note: the Pleiades rise at dawn in June. Pure dingoes generally breed from March to June, meaning the first litters are birthing in May and June, since the gestation period is about 9 weeks. Wallaby&rsquos breed from January to February, and borth after 28 days. They stay in the pouch for another two months, meaning they start roaming about around May and June, the time dingoes are pursuing them for food.

Teachers can discuss with the students the needs of the people reflected in the calendar, and how the stars can inform seasonal change related to animal behaviour.

### Notes

1 Hamacher, D.W., Tapim, A., Passi, S. and Barsa, J. (2018). &lsquoDancing with the stars&rsquo &ndash Astronomy and Music in the Torres Strait. In: N. Campion and C. Impey (eds) Imagining Other Worlds: Explorations in Astronomy and Culture, Sophia Centre Press. Lampeter, UK. pp. 151-161.

2 Clarke, P.A. (2009). Australian Aboriginal ethnometeorology and seasonal calendars. History & Anthropology, 20(2), 79&ndash106.

4 Hamacher, D.W. (2015). Identifying seasonal stars in Kaurna astronomical traditions. Journal of Astronomical History and Heritage, 18(1), 39-52.

6 Leaman, T.M., Hamacher, D.W. and Carter, M.T. (2016). Aboriginal Astronomical traditions from Ooldea, South Australia, Part 2: Animals in the Ooldean sky. Journal of Astronomical History and Heritage, 19(1), 61-78.

7 Leaman, T.M. and Hamacher, D.W. (2014). Aboriginal Astronomical traditions from Ooldea, South Australia, Part 1: Nyeeruna and &lsquoThe Orion Story&rsquo. Journal of Astronomical History and Heritage, 17(2), 180-191.

8 Johnson, D.D. (2011). Interpretations of the Pleiades in Australian Aboriginal astronomies. In Archaeoastronomy & Ethnoastronomy &ndash Building Bridges Between Cultures, edited by Clive Ruggles. Cambridge University Press, pp. 291-297.

9 Fuller, R.S., Anderson, M.G., Norris, R.P. and Trudgett, M. (2014). The Emu sky knowledge of the Kamilaroi and Euahlayi peoples. Journal of Astronomical History and Heritage, 17(2), 171-179.

11 Mountford, C.P. (1958) The Tiwi. London: Phoenix House, pp. 175-177.

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## Comparison With Modern Science

The standard values for the tropical year and annual precession in longitude determined by Simon Newcomb for the epoch 1900.0, mean noon at Greenwich December 31st 1899 are:

 One tropical year = 365.2421988 Precession in one year = 50".2564

The sidereal year and its precessional constant may be derived from these values.

 1 sidereal year (1900.0) = 360° 360° - 50".2564 × 365.2421988 + 1 = 366.2563627 diurnal revolutions of the Earth
 Precession in longitude in one year = 50".2564 × 365.2563627 365.2421988 = 50".2583

The following shows the astronomical quantities used in the construction of Hindu cosmological time cycles with those of Simon Newcomb for the epoch 1900.0

HinduNewcombDifference
Constant of Precession50".4 / year50".2583 / year0".1417 / year
Sidereal Year (Solar)365.2563795365.25636271.4 seconds / year
Tropical Year365.2421756365.2421988-2.0 seconds / year

The sidereal year in the above table refers to the number of solar civil days it takes for the earth to orbit the sun in relation to any particular star. The former is a sidereal-diurnal relation and the later is a sidereal-solar relation. The very close agreement between the length of the year as measured by Hindu cosmological time cycles and that determined by modern science, together with the demonstrated great antiquity of the cycles, shows that the rotation of the Earth is not being sensibly retarded by "tidal friction" or any other cause.