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If you want to have a smaller star but you also want to keep your planet in the habitable zone, you need to put the planet closer to the star. This means shorter years.
It is also possible to have a larger star and a longer year.

Specifications: The planet is not tidal locked to the star. To have any significance, keep in mind that the years would need to be at least twice as long or half a normal year on Earth.

The length of a day would be the same as on Earth.

Edit: the axial tilt of the planet is exactly the same as Earth and stable at 23,5°

Vincent
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    For an interesting angle on this you might look at Brian Aldiss Heliconia stories ( or to a degree A Song Of Ice And Fire ) both of which are set on worlds that belong to a binary star system where one star creates a regular day/night/year cycle and the other creates a much slower phased long season cycle over decades or centuries. – glenatron Oct 08 '14 at 13:20

3 Answers3

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There is one massive difference this will make - the duration of the seasons.

A longer year would give you extremely long (but potentially dry and drought-prone) summers followed by equally long winters. This means that storage of food would be a priority in seasonal areas of the world (the equator would not be effected either way).

So the summer would be an extremely long growing period while people stocked up to survive months or even (earth) years of winter. Animals may well hibernate or just lay eggs/spores/whatever that then emerge when spring comes. A lot of plants may well follow the same strategy of leaving seeds and not even trying to survive the winter.

Tim B
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    Will it? Seasons are based on the tilt of the planet and the distance from the sun during it's orbit...not necessarily the duration of the orbit. Would it be possible to have twice the length year and 8 seasons instead? (I don't have an answer here, more of a curiosity) – Twelfth Oct 08 '14 at 03:08
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    @Twelfth Unless the axial tilt of the planet varies very quickly, or there is some special configurations with several stars (or a massive planet), there will always be one summer and one winter on a planet. note that on our planet, the distance to the sun is not a relevant factor, since it barely varies. – overactor Oct 08 '14 at 06:17
  • Though maybe if the orbit of this planet was more eccentric, the interplay between distance to the star and axial tilt could result in more than one summer at some places on this planet. – overactor Oct 08 '14 at 06:19
  • @Twelfth If you think about it you have Sun o and planet with axis /... then o/ is summer southern hemisphere, winter northern /o is summer northern, winter southern. The axis always points the same direction as the planet orbits so each season is always once per year (in a standard single primary system). – Tim B Oct 08 '14 at 08:08
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    That makes sense, thanks for the clarify. The planet would really need an odd wobble to have spuratic seasons. – Twelfth Oct 08 '14 at 16:50
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I'm actually going to consider how such a year would affect animals, because I have a feeling nobody else is planning on addressing it. This should be short and to the point, unlike some of my other answers.

Many animals have a "mating season" - i.e. a period each year where they mate. This can manifest itself in brilliant displays of plumage, or head-butting confrontations between some males. For many species, the mating season only comes once a year, and so each female only gives birth to a small number of offspring.

Now, if the year was longer, and there was still only one mating season per year, each female (and therefore each male) would produce only half as many offspring throughout their lives as they would otherwise. If the year was shorter, each female (and therefore each male) would produce twice as many offspring throughout their lives as they would otherwise. Thus, population growth could be affected by a change in the length of a year. Note: This assumes gestation period remains the same, which may not be the case.

HDE 226868
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As far as I know, the length of the day is more important than than the length of the year. It may have an effect on how long seasons last, but assuming they last at least a month or so, I don't think there would be changes that drastic (seasons heavily depend on axial tilt, so that also has to be taken into account - if the tilt is like Earths, they'd probably last a bit less than ours). If all else is the same, climates would be distributed the same and you could just move to a more friendly one. The ecosystems would adapt, possibly with biomes being a bit smaller to cut distances, but they should be fine overall.

A larger factor would be how much the year length varies - if there is a lot of variance (as in, one year lasting 4 times as long as the previous for instance), there would probably be a much higher influence, but it would be because ecosystems would have difficulty managing their cycle.

Overall, the differences should be minor, if they exist at all (assuming all else is the same).

mechalynx
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  • I don't think you are taking into account the affect the lenght of seasons have on growing things. Plants could adjust how long they take to mature, otherwise its going to be a hard life. – Vulcronos Oct 07 '14 at 20:41
  • @Vulcronos well it's a tough point to answer when, everything's the same, except the year length. If life evolved with this longer or shorter year length, but is otherwise the same, there's a contradiction. Has it adapted to this length? If so, there's likely going to be different plant life - but if everything is the same, then it takes just as much to mature but probably takes more care to make it work. We already cultivate plants outside their natural cycle, so it might slow down population growth, but even that's a lot to assume considering the possible contradictions and side-effects. – mechalynx Oct 07 '14 at 20:46
  • Yeah. I just wanted to bring the point up if you wanted to address your answer. – Vulcronos Oct 07 '14 at 21:01
  • @Vulcronos that's fine, I just don't know how to deal with the issue, the comments will have to do for now. – mechalynx Oct 07 '14 at 21:04
  • I admit that part '' everything else is the same'' is very confusing. I was not thinking at anything in particular. I can get rid of that. Life should be different indeed. – Vincent Oct 08 '14 at 02:43
  • @Vincent Yeah but at the same time, you can't really broaden it enough to include all possible effects and differences without having it get too broad. A good idea would be to tell us about the axial tilt and how it varies across the year, since most of us have been commenting on that detail. – mechalynx Oct 08 '14 at 11:22
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    it should stay the same at 23,5 degrees, like ours. It's not instable because it would make life almost impossible there. – Vincent Oct 08 '14 at 17:52