Before writing a story of another world we must build that world. First, we need to know which star is that world's life and energy source. Different stars require different conditions to evolve life-bearing planets.
There are roughly five hundred stars proximal to Sol. Thirty are believed to be potentially life-supporting systems. To find an appropriate star our characters would search these Sol-similar stars for those nearest to Sol.
Sol is a type G, yellowish-white dwarf star. All the theorists believe spectral classes G and K stars are the most likely to have life-supporting planets. However, such stars are also most likely to be in multiple star systems. You can have a multiple star system or a planetary system, not both. There are four excellent possibilities in Sol's immediate neighborhood: Delta Pavonis, Tau Ceti, Epsilon Eridani, and Epsilon Indi.
Delta Pavonis is in the constellation of Pavo (The Peacock). It cannot be seen from North America. In the January sky Delta Pavonis is located forty degrees south latitude - south of Melbourne, Australia. Nineteen light-years from Sol. This is approximately one hundred fourteen trillion miles. Relatively close - for interstellar distances.
Although Delta Pavonis is slightly smaller in size and mass than Sol, its temperature is the same. As a yellow dwarf - and virtual twin sister to Sol - it is highly possible Delta Pavonis has an earth-like planet. If so, we would find her life-belt the same as Sol's, some eighty million to one hundred million miles from the primary.
Tau Ceti is the twentieth closest star to Sol. It is located approximately 11.8 light years away in the constellation Cetus (The Whale). Cetus is a large constellation straddling, and overlapping the celestial equator, albeit mainly in the southern hemisphere. In the October sky, Cetus is bounded on the west by Aquarius, and in the north by Taurus.
Tau Ceti is a solar-type star, a star with the same spectrum, temperature, and other properties as Sol. Therefore, like Delta Pavonis, Tau Ceti's life belt would be the same as Sol's.
Our third possible star, Epsilon Eridani, is 10.8 light years away in the constellation Eridanus (The River). Epsilon Eridani is the star classification K. This means Epsilon Eridani is slightly cooler than Sol, and orange in color. We could expect Epsilon Eridani's life-belt to be closer than Sol's. However, if we choose this star our planet cannot be at the life-belt's inner edge. The closer a planet is to its primary the slower the planet's rotation. A planet that takes nearly an Earth year for one day to pass (like Venus) is too hot for life-bearing.
Our final star, Epsilon Indi, is between 11.2 and 11.6 light years from Sol. Epsilon Indi is classification K, and located in the Indus constellation (The Indian). Indus, is a
few celestial degrees north of Pavo in the southern hemisphere. Having established possible near-by stars to take our explorers to, we now turn to designing the planet itself. A migration-friendly planet must be earth-like in size and composition. It must revolve within the life-belt boundaries. There is no guarantee that these conditions exist. But it is possible.
The degree of axial tilt which causes seasonal changes - or the lack thereof - must be considered. If there is no tilt there would be little seasonal change. The temperatures would vary from hottest at the equator to coolest at the poles. Gradually jungles give way to forests, which would thin and surrender to tundra. Tundra would abut permanent, miles deep, ice and snow.
There are many other factors in climate. Albedo, atmosphere composition, volcanic activity, the percentage of oceans and seas to land, whether or not there are high mountains to deflect air currents. All this and more has a part in the final results. For reasons I will go into in part three - alien cultures - our planet is relatively even with no elevation higher than a good sized hill. The seas are narrow and shallow. They are no great barrier to movement, nor likely to cause great cooling. Our planet encircles the star Delta Pavonis, and has no axial tilt.
If our theoretical planet were situated on the life-belt's inner rim, one expects a warm planet rich in tropical rain forests, as once Venus was thought to have. If located in the life-belt's center section, a temperate planet is expected, much like Earth's Mediterranean countries or Southern California. An orbit on the life-belt's outer rim provides a cooler climate, perhaps like southern Canada.
I am partial to cooler climates so our planet encircles Delta Pavonis near the life-belt's outer rim. Our explorers have high expectations and have name the planet Rhyannon, after the ancient Celtic goddess of wit and wisdom. Rhyannon is heavily forested with some grasslands and narrow, shallow seas.
Having decided this, we now determine if Rhyannon has intelligent life for our humans to encounter. Stories need conflict. So Rhyannon is occupied by a specie every bit humanity's intellectual equal. In part three, I go into developing our aliens and their culture.