Stars, Planets, Natural Satellites

In the Deathworld universe, there are a number of astronomical bodies of note. In Deathworld, Jason dinAlt begins his journey from the planet Cassylia where he won 3 billion credits for Kerk. From there he accompanies Kerk to Darkhan where they board the Pyrran ship piloted by Meta and travel to Pyrrus.

In Deathworld 2 (The Ethical Engineer), Jason is kidnapped by Mikah Simon to take him back to Cassylia, but they crash land on a planet in the system DB89-046-229, but is rescued later by Meta.

In Deathworld 3 (The Horse Barbarians), Jason buys a spaceship and takes some 169 Pyrrans to Felicity, but stop at a transfer station in the 70 Ophiuchi system.

There is but limited information about the suns, planets, and moons of the Deathworld universe, but, with the given information we get from the novels we can infer much using the tools of astronomy.

# Stars

Stars are bodies ranging from brown dwarfs, which are almost stars, creating energy by the fusion of deuterium (hydrogen nuclei with one proton and one neutron) to produce helium. Real stars begin with red dwarfs, with mass ranging from 0.075 solar mass up to about 0.5 solar mass) and continue up to blue giants (with mass as high as 75 solar masses), all creating energy by the fusion of four hydrogen nuclei to produce helium. These are the 'main sequence' stars, which are stars in the middle of their lifespan beginning with ignition of the hydrogen core until the star uses up most of its hydrogen, then it leaves the main sequence and other things begin to happen depending on its mass. Other types such as red giant, white dwarf, etc are beyond the scope of this article. See star at Wikiepedia.

Stars are classified by letters to designate their mass, color and other characteristics. Each star type depends pretty much solely on its mass such as size, color, temperature, etc. Stellar classification are given by letters as follows: OBAFGKM, beginning with the largest stars through the smallest. You can remember this sequence with the words "**O**h **B**e **A** **F**ine **G**irl, **K**iss **M**e.

## 70 Ophiuchi

70 Ophiuchi is binary system in the constellation Ophiuchus as seen from the point of view of Earth.

70 Ophiuchi A is is a K0 main sequence yellow dwarf star with a mass of 0.9 times the mass of the Earth's Sun, 70 Ophiuchi B is an orange star with a mass of 0.7 time the mass of the sun. They are in elliptical orbits at an eccentricity of 0.495, such that the distance between them ranges from 11.4 to 34.8 AU, the average distance is about 23 AU. The Transfer Station 70 Ophiuchi is at the L1 point between A and B.

## Earth's sun

**Earth's Sun** is a G2V star, just a bit bigger than a standard G type star, mass is 1.98855×1030 kg, equatorial radius is 695700 km, volume is 1.41×1018 km3. Surface temperature is 5,778K. When comparing stars, the sun's mass is the standard at one solar mass.

## DB89-046-229

Nothing is known of the star **DB89-046-229**.

## Cassylia's and Darkhan's Sun

There is no description of the sun around which Cassylia and Darkhan orbit.

## Felicity's Sun

**Felicity's Sun** is given in Deathworld 3 (The Horse Barbarians) as an F1 star. From this we can infur some data. Despite the conventional description as a white-yellow star, an F1 star appears white, surface temperature is about 7300K, mass is about 1.3 solar masses, radius is about 1.3 solar radii, luminosity is 1.38 times that of the Earth's Sun, and the absolute magnitude is about 3.3, and as was given in the novel, an F2 star produces more ultraviolet light than the Earth's Sun.

## Pyrrus' Sun

As a G2 sun, **Pyrrus' Sun** would be virtually identical in description as Earth's Sun.

# Planets

Currently, if take the current definition of a planet and extend it to other stars, a planet orbits one or more stars in a system, is big enough that its gravity makes itself round, and has cleared it's orbital neighborhood of almost all of the debris. Anything smaller is a small system body; anything bigger is either a brown dwarf or a star. In the Deathworld universe, there are at least thirty thousand planets that have been inhabited by humans. Some of these planets have become culturally isolated as a result of the galactic war a couple of hundred years before the novels.

## Cassylia

Not much is known about **Cassylia** except that if it is inhabited by humans, it has an atmosphere that is not unlike that of Earth, the atmosphere is likely an nitrogen-oxygen mixture with other trace gases and some amount of water vapor. There is likely a subsantial amount of liquid water on the surface, and temperature range must be similar to that of earth. In all respects, it appears to be very earthlike.

## Darkhan

**Darkhan** is likely a near enough twin of Cassylia with a similar history of formation.

## Earth

**Earth** is our planet and origin of all humans that have inhabited the Deathworld universe. The Earth is the third planet in order from the Sun. It has a mass of 5.97237×1024 kg, and rocky planets are compared in mass to the earth's mass. Radius is 6371 km. Surface gravity is 9.807 m/sec2 which is the standard 1G when comparing gravity on other bodies. Sidereal rotation period, the time to rotate once is 23h 56m 4.1s. Because of it's orbit around the sun results in the average solar day being 24 hours. The Earth is in a slightly elliptical orbit around the Sun which takes 365.256363004 days to complete one orbit, the year. Average distance from the sun is 149,598,023 km, which is used as a standard, the Astronomical Unit, or AU. The density of the Earth is 5.514 gm/cm3, the densest planet in our solar system.

## Felicity

**Felicity** is a planet with approximately 1½ times the surface gravity as the Earth. Given this, some other data about the planet can be inferred.

We know that there is an abundance of heavy metals in a particular area of the northern continent, but, the density of the planet is unknown. Let's use the earth's density as a starting point. The density of the Earth is 5.517 gm/cm3 or 5514 Kg/m3, and it is the densest planet in our solar system. The acceleration due to gravity at the surface of the earth is 9.807 m/sec2. So, acceleration at the surface of Felicity is 1½ time that or 14.71 m/sec2. We can use the gravity equation *m=ar2/G*, where *m* is the mass of Felicity, *a* is 14.71 m/sec2, *r* is the radius which we will assume the radius of the planet is 1.5 times Earth or 9,556,500 or 9.5565×106 meters to start, and *G* is the gravitational constant, 6.6726×10-11 Nm2/Kg2. So, *m*=14.71×(9.5565×106)2/6.6726×10-11 equals a mass of 2.0133×1025 Kg. If we assume the density of Felicity is the same as the Earth, 5514 Kg/m3, we have 2.0133×1025÷5514=3.6513×1021 cubic meters, or 3.6513×1012 cubic kilometers. Now, let's check our work. Taking the equation for volume, *V=4πr3/3*, solving for *r*, *r3=3V/4π*, 3×3.6513×1012/(4\*3.141592654)=(8.7169×1020)1/3=9552564 meters or 9552 km, which is in fairly good agreement with the 9,556 km we used for an assumption, considering rounding off errors. With the heavy metals the Pyrrans are after on Felicity, the density is not likely to be less, making the planet larger, it may be denser, making the planet slightly smaller. So, the 9665 km radius would be considered the upper limit. The axial tilt was given in the novel as almost exactly zero so the the seasons were static. The day is 20 hours long compared to 24 hours on the Earth.

Now, let's consider its orbit. The Earth's average distance from the Sun (semimajor axis) is 149,600,000 km. Since the luminosity of Felicity's Sun is 4 to 4½ times that of our Sun, let's use 4.25. Using the inverse square law, where, doubling the distance cuts the energy received by one-quarter, a planet