Q 01/05

What is the shadow-casting part of a sundial called?

A) Style

B) Gnomon

C) Nodus

D) Dial plate

Answer · why

B) Gnomon

The word comes from Ancient Greek for 'one that knows or examines'; only its time-telling edge is called the style.

Q 02/05

How many degrees does the Sun appear to move around Earth's axis each hour?

A) 5°

B) 10°

C) 12°

D) 15°

Answer · why

D) 15°

That is why the hour lines on a dial whose plate faces the celestial pole are evenly spaced.

Q 03/05

For a sundial to be accurate all year, its style must be parallel to what?

A) The local horizon

B) Earth's rotational axis

C) The line to magnetic north

D) The plane of the ecliptic

Answer · why

B) Earth's rotational axis

That alignment is what makes the shadow sweep round at a constant rate whatever the season.

Q 04/05

What must a horizontal sundial's style angle above the horizontal equal?

A) The Sun's declination

B) The axial tilt of 23.5°

C) The local longitude

D) The local latitude

Answer · why

D) The local latitude

A dial built for London therefore does not keep good time in Cairo unless it is tilted.

Q 05/05

What is the single time-telling point, such as a style tip, on a sundial called?

A) Analemma

B) Nodus

C) Substyle

D) Meridian

Answer · why

B) Nodus

The path traced by a nodus over a day is a conic section such as a hyperbola.