Comparative Planetology and Observing Earth’s Neighbors

Mercury

This planet is a small, incredibly hot world with a weaker version of Earth's magnetic field throughout the entire planet.

Venus

This planet has a sweltering climate. It is hotter than Mercury, despite being farther from the Sun.

Greenhouse Effect

The process by which atmospheric gases raise the temperature by absorbing outward-flowing heat.

Mars

This planet is too chilly for life to exist

Mercury

It has many craters like the Moon, but it also has a molten iron core that creates a magnetic field, just like Earth.

Venus

This planet is considered as Earth’s evil twin.

Mars

This planet is the miniature Earth that dried up and cooled.

Morning Star

A bright planet appearing in the east before dawn.

Evening Star

A bright planet appearing in the west after sunset.

Elongation

It is the angular separation between a planet and the Sun, as visible from Earth.

Greatest western or eastern elongation

These happen when a planet is at its farthest possible distance from the Sun during a specific apparition.

Apparition

A period of time when the planet is visible from Earth on successive nights.

Opposition

It occurs when a planet is on the opposite side of Earth from the Sun.

Conjunction

It occurs when two solar system objects are near each other in the sky, such as when the Moon passes near Venus as we see them.

Ascension

The position of a star measured in the east–west direction.

Declination

The position of a star measured in the north-south direction.

Ecliptic

A circle in the sky that represents the path of the Sun through the constellations.

Ecliptic Latitude and Longitude

Measure degrees north and south or east and west with respect to the ecliptic.

Superior Planet

It orbits outside the orbit of Earth

Inferior Planet

It orbits inside the orbit of Earth.

Averted Vision

Glimpse out of the corner of your eye.

Terminator

The dividing line between the bright and dark parts of Venus.

Ashen Light

The pale glow on the dark part of Venus.

Planetary Transit

When a planet passes right in front of the Sun and looks like a tiny black disk against the bright solar surface.

Sytris Major

A large dark area on Mars extending northward from the equator.

Albedo Map

It maps and identifies the bright and dark regions of Mars that are visible using a tiny telescope. It provides more information than the typical observer ever sees, serves as a useful guide, and tests your observational abilities.

Seeing

The steadiness of the atmosphere above the telescope.

Transparency

The freedom from clouds and haze.

Darkness

The freedom from interfering artificial light, moonlight, or sunlight.

western elongation

Mercury is easiest to observe when it is at _____ and appears in the early morning twilight.

6 - 8

At its greatest elongation, Mercury appears to be only ____ arc seconds in size.