Elong. is a planet's elongation: the angle between the Sun and the planet.
It measures the visual distance of a planet from the Sun, as seen from Earth, with values from 0 to 180° degrees.
A planet with an elongation close to 180° is visible on the meridian at midnight local time.
Dist. is a planet's distance from the Earth in astronomical units (mean distance between Earth and Sun).
Planets appear larger through a telescope when they are closer to the Earth for better viewing opportunities.
Graphic: the above image shows the Sun and planets on the ecliptic,
with the exception of the Earth, the observer's location.
Planets to the left of the Sun in the above graphic are visible after sunset,
and planets shown to the right of the Sun are best visible before sunrise.
Planets are not visible when they are too close to the Sun (elongation < 15°) except during total solar eclipses.