A Quiz for the Astro-Savvy

Answer: Blue

Massive stars in the main sequence stage tend to be blue in color, with surface temperatures exceeding 30,000 K. This can be deduced from the H-R diagram.

Answer: 8.6 light-years

Sirius is the brightest star in the night sky and is located a mere 8.6 light-years away from Earth. With an apparent magnitude of -1.46, it's more than twice as massive as the Sun and is part of a binary system.

Answer: Venus

Venus has often been regarded as Earth's sister planet due, in large part, to the physical similarities of the two worlds, such as their sizes and masses.

Answer: Tidal acceleration

As the Moon orbits the Earth, its gravity creates a 'bulge' on the side of the Earth closest to it. Because the Earth rotates faster than the Moon orbits the Earth, this bulge goes slightly ahead of the Moon, while also pulling the Moon along. This net torque boosts the Moon in its orbit and causes it to recede from the Earth. Due to the conservation of angular momentum, the Earth's rotation, meanwhile, slows down.

As a consequence of this process, known as tidal acceleration, the length of the day is gradually getting longer while the Moon is moving away from us.

Answer: Titan has a far lower temperature than the Moon, which helps it retain an atmosphere in spite of its lower surface gravity

The difference in temperature is the main reason for this. The Moon is located at 1 AU from the Sun, whereas Titan is located at 9.5 AU from the Sun, nearly ten times as far. Such a difference in distance normally results in considerable variations in temperature. Chemical reactions in Titan's atmosphere are very slow because of this lower temperature.

As a consequence, the molecular velocity of the atmosphere is slow and thus the atmosphere remains as it is and keeps hanging around indefinitely. If the same atmosphere were placed on the Moon, the increased heat from the Sun would cause it to burn away in a geologically short span of time.

Answer: Having an axial tilt

An axial tilt, also known as obliquity, is required for a planet to experience seasons. The Earth's seasons occur because the planet's axis of rotation is tilted at an angle of 23.5 degrees relative to the orbital plane. Contrary to popular belief, our varying distance from the Sun is NOT a reason behind the seasons.

Answer: Water vapor breaking down, causing hydrogen loss and oxidized rocks

When water vapor breaks down (e.g. due to intense temperatures), the light hydrogen dissipates and escapes into space. Meanwhile, the remaining free oxygen reacts with rocks to oxidize them, often creating what is known as iron oxide. This gives a planetary surface a reddish tint, much like Mars. (This is also essentially the same process that causes rust.)

Answer: 22.1 AU

To find the semimajor axis (i.e. average orbital distance) of a planet given the mass of the parent star and the planet's orbital period, we use a modified version of Kepler's third law, which is in the form:

R^3 = (GMT^2)/(4ð^2 )

Where

R = the planet's semimajor axis (in meters)
G = the gravitational constant
M = the mass of the star (in kg)
T = the orbital period (in seconds)

Simply plugging in the values and performing the required conversions yields a distance value of about 22.1 AU for our planet. (Recall that an astronomical unit is the average distance between the Earth and the Sun, which is about 150 million km.)

Answer: 45 km/s

To find the orbital velocity of a planet given the mass of the host star, we use the formula:

V^2 = (GM/R)

Where

V = the orbital velocity of the planet (in meters per second)
G = the gravitational constant
M = the mass of the host star (in kg)
R = the semimajor axis of the planet (in meters)

In this case, the planet's orbital velocity comes out to about 45 km/sec. This is close to Mercury's velocity around the Sun.

Answer: Organic components

Organic components, particularly molecules with carbon and hydrogen, are one of the three main prerequisites for life to develop, the other two being an energy source (like the Sun) and water.