Fireball system:
Large star, giving white-blue light. Planets are spread much wider than the Sun’s, showing dim points at night, interplanetary travel is much slower. HZ is broader, further out.
Basic stats:
| Age range: | Habitable zone*: | Dimensions: | Radiation levels: | Opportunities: | Hazards: | Visuals in brief: |
| Up to around a billion years old. | Inner edge:
2.7 AU
Outer edge:
6 AU
| Radius: 1.8 Rs
Mass: 1.9 MS
Surface Temp: 8250 ℃ | More UV in the star’s light - between 2 to 10 times as much exposure in the star’s habitable zone, compared to Earth. X-ray levels are almost zero. |
- Broader habitable zone - allowing multiple Earth-like worlds.
- Fewer damaging solar particle storms at habitable zone
|
- Wider spaced solar system, with longer interplanetary travel times.
- 2 to 10 times as much UV exposure for an Earth-like planet in the habitable zone
- Habitable planets will be volcanic, younger.
| The blue-white star (A5 type), as seen from a habitable planet: A5 type stars give a blue-tinged white light (true white as seen through an earth-like atmosphere), with a much higher surface temperature and luminosity than Earth’s Sun. Their habitable zones are generally further out so they appear smaller from any habitable planets - around a half to a fifth as wide as the Sun seen from Earth.
The daytime sky of a habitable planet: The sky of an Earth-like planet orbiting a type A star would (barring contaminants) be more intense blue, evn tending towards indigo, than Earth’s. Sunsets will be white, or very faint yellow.
The night sky of a habitable planet: Comets will show tails for longer than those orbiting our Sun, and auroras will be rare and fainter, owing to the weaker solar wind. Zodiacal light will be much brighter than Earth’s.
Other planets: Other planets will appear as star-like points. They may be considerably fainter than those seen from Earth, only changing positions against the background sky over terrestrial years or decades, as the system has room to be much more widely spaced. |
Travel within the system:
| Travel methods and speeds: | Travel times from an orbit on the Habitable Zone’s (HZ) inner edge (2.7 AU) to one… | | |
| ...on the Habitable Zone's outer edge (6 AU) | ..with Mercury-like heat ( 1.5 AU): | .. with Neptune-like cold (105 AU): |
| Chemical rocket speeds (by Hohman transfer orbit) Up to 25 km/sec* | 3 years 4 months
| 1 year 2 months | 140 years |
| Sublight probe/arkship speeds** 15,000 km/sec (5% lightspeed) | 9 hrs 10 min | 3 hrs 20 min | 12 days |
| At lightspeed 299,792 km/sec | 28 minutes | 10 minutes | 14 hrs 30 mins |
** Not factoring acceleration and deceleration time - see p??? [ link] for more explanation
Notes on the blue-white star (A-5 type star) and system:
The blue-white (type A5) star: Type A5 stars are much larger and hotter than our Sun, with habitable zones further out so, despite being wider than the Sun they appear smaller from habitable planets. They are younger, and faster spinning, which affects their shape and pattern of surface brightness. They also lack a convective outer layer (see p??? [link}) , so the starspots and patterns of granules of sun-like stars may only occur at the equator. They live for a billion years (1/10th as long as our Sun) - time for simple life to arise, but multi-cell life is less likely. Under 1% of our galaxy’s stars are A type.
The surrounding system: The system is much broader than Earth’s, so planets may be much more widely spread - or you might in more: Multiple gas giants with large moon systems, and at least as many solid-surfaced worlds as our solar system has. The solid worlds are likely to be geologically active, with frequent powerful quakes and eruptions: Normal volcanoes occur on worlds in the HZ or closer, allowing even small worlds to have atmospheres. Icy worlds, further out, will have cryovolcanic (see p??? [link}) eruptions, bringing water and ammonia slurries to their surface. Interplanetary space in the system will have more asteroids and dust, a far weaker solar wind, with few particle storms. The orbits of outer giant planets may extend to hundreds of AU with years lasting terrestrial centuries, or even millenia. Habitable worlds will have years lasting terrestrial decades.
Visuals from an Earth-like planet in the habitable zone:
The blue-white central star: The star itself could appear ½ to ¼, the Sun’s apparent size. The light tone is blue-tinged white, and it may appear slightly flattened, as its fast rotation pulls it into a tangerine shape. The rotation reduces the temperature and brightness of the equator, so the sun’s brightness (when viewable, for example through cloud or fog) will be concentrated at the poles. After passing through the atmosphere the star would appear less blue, more true-white.
Sky colour: The sky of an Earth-like planet orbiting a type A star would (barring contaminants) be brighter, stronger blue than Earth’s. Sunsets will be white, or very faint yellow. Blue sky is caused by the blue component of sunlight being scattered by the gas molecules making up our atmosphere - these are closer in size to the wavelength of blue light than the wavelength of red, so they scatter blue light much more efficiently across the sky. The same would happen for a world with an A type sun, but with less of a blue in its light the blue colour would be more intense.
Plant colour: Photosynthetic plants may be based on violet, yellow and red pigments, giving a red-purple colour to take advantage of the more blue-rich light.
Other sky phenomena: Aurora will be far rarer and fainter than Earth’s, owing to the lack of flares and CME particle storms. Comets will develop tails much further out, which will last longer, owing to the greater warmth from the star. The zodiacal light (see glossary, p??? [link]) will be brighter than Earth’s, creating a ‘false dawn’ effect.
Hazards: Interplanetary travel times will be longer, and would need more energy due to the central star’s higher gravity. UV exposure in the habitable zone will be 2-10 x higher, possibly driving life underground. Asteroids are more common, resulting in more impacts (see glossary, p??? [link]). The star itself, despite being calmer, is the greatest hazard, as ....
