Eclipses: question bank

Q1

FoundationShadows, umbra and penumbra, and eye safety

What is the umbra part of a shadow?

The fully dark middle, where the light source is completely hiddenThe grey fringe where part of the light source still showsThe brightest part of a shadowA shadow that only forms at night

Q2

FoundationShadows, umbra and penumbra, and eye safety

Why can never look at the Sun without a certified filter, even during a deep partial eclipse?

Because the Sun's surface is still blazingly bright even when mostly coveredBecause eclipses attract more ultraviolet light than usualBecause the Moon reflects harmful raysIt is only a superstition, not a real risk

Q3

FoundationShadows, umbra and penumbra, and eye safety

Which of these is a genuinely safe way to watch a partial solar eclipse?

Sunglasses, even several pairs stackedA pinhole in a card, projecting an image onto paperLooking through a phone cameraA quick glance, since it only takes a second

Q4

FoundationShadows, umbra and penumbra, and eye safety

True or false: sunglasses, even several pairs worn together, are safe for viewing a partial solar eclipse.

TrueFalse

Q5

CoreShadows, umbra and penumbra, and eye safety

Certified eclipse glasses (ISO 12312-2) transmit about 0.0032% of visible light. Roughly how many times dimmer is that than looking at the Sun with bare eyes? Round to the nearest 1,000.

Your answer

Q6

CoreShadows, umbra and penumbra, and eye safety

Why is looking at the Sun through binoculars dangerous even while wearing certified eclipse glasses over your eyes?

The binoculars gather and concentrate the sunlight before it reaches the filter, which can melt or crack itBinoculars make the glasses fall offIt is not dangerous, this is a safe combinationBinoculars block too much light, making nothing visible

Q7

CoreShadows, umbra and penumbra, and eye safety

Why is retinal damage from looking at the Sun especially dangerous, compared with, say, touching something hot?

It heals faster than a burnThe retina has no pain nerves, so the damage is painless and often unnoticed until hours laterIt only affects one eyeIt causes an immediate, obvious headache

Q8

StretchShadows, umbra and penumbra, and eye safety

A 4 cm ball is held 20 cm from a small point lamp, with a screen 60 cm from the lamp. How wide, in cm, is the shadow on the screen?

Your answer (cm)

Q9

StretchShadows, umbra and penumbra, and eye safety

In the same set-up, the ball is moved to 40 cm from the lamp (screen still at 60 cm). How wide is the shadow now, in cm?

Your answer (cm)

Q10

ChallengeShadows, umbra and penumbra, and eye safety

A pinhole camera makes an image of the Sun about 9.3 mm across for every metre of distance between the pinhole and the screen. Why is this rate roughly constant regardless of how big or small the pinhole's hole itself is (as long as it stays small and clean)?

The image size is set by the Sun's fixed angular width and the screen distance, not by the hole's sizeBigger holes always make bigger images, so the rate actually changes with hole sizeIt is a coincidence with no underlying reasonThe rate only holds for holes exactly 1 mm wide

Q11

FoundationSolar vs lunar eclipses

In a solar eclipse, whose shadow falls on what?

The Moon's shadow falls on EarthEarth's shadow falls on the MoonThe Sun's shadow falls on EarthEarth's shadow falls on the Sun

Q12

FoundationSolar vs lunar eclipses

At which Moon phase must a solar eclipse always happen?

Full moonFirst quarterNew moonAny phase at all

Q13

FoundationSolar vs lunar eclipses

At which Moon phase must a lunar eclipse always happen?

New moonFull moonLast quarterAny phase at all

Q14

FoundationSolar vs lunar eclipses

Why does an eclipsed Moon turn red instead of simply going black?

It reflects light from MarsSunlight bent through Earth's atmosphere reaches it, and that light has lost most of its blueThe Moon glows with its own heatIt is an optical illusion caused by the dark sky

Q15

CoreSolar vs lunar eclipses

A photo taken at 9 p.m. shows a reddish Moon with a dark curved bite out of one side, with stars visible nearby. What kind of eclipse is this?

A total solar eclipseA partial lunar eclipseAn annular solar eclipseA penumbral solar eclipse

All 68 questions