Solar and lunar eclipses: how they differ and why only one can be watched without glasses

In a solar eclipse, the Moon moves between the Sun and the Earth and hides the Sun from us; it can only happen at new moon, and totality can only be seen from a narrow path. In a lunar eclipse, it is the Earth that moves between the Sun and the Moon, and its shadow falls on the full Moon; it can be seen from the whole half of the planet where it is night. A lunar eclipse can be watched without any protection; a solar eclipse, never without a filter, except during the minutes of totality. The eclipse of 2 August 2027 is a solar one.

The differences at a glance

Who covers whom

According to NASA, a solar eclipse happens when the Moon passes between the Sun and the Earth, and a lunar eclipse when the Earth lines up exactly between the Moon and the Sun, which is why it always falls at full moon. Wikipedia adds that a solar eclipse can only happen at new moon, and only near one of the two points where the Moon’s orbit crosses the Sun’s path across the sky. Why that doesn’t happen every month is explained with drawings in our learn section.

Since a full moon is needed, there can be no lunar eclipse on 2 August 2027, a new-moon day: we explain it in the eclipses of 2027.

Where it can be seen from

Space Place, NASA’s site for children, explains it like this: to see a solar eclipse you have to be on the side of the planet where it is daytime and, on top of that, in the path of the Moon’s shadow. Totality, says Wikipedia, only happens along a narrow strip of the surface; outside it, according to NASA, you see a partial eclipse. In 2027 that strip is about 258 km wide at its widest, and in Spain only 105 municipalities fall inside it, all in the south, Ceuta and Melilla included. Madrid will be left with a partial eclipse of 86.1%.

A lunar eclipse, on the other hand, can be seen by anyone with the Moon above the horizon. According to Space Place, you will be able to see it if you live on the half of the Earth where it is night while it happens, so there’s no need to travel.

How long it lasts

A solar totality is measured in minutes. According to Wikipedia, today it cannot exceed 7 min 32 s. The 2027 one reaches 6 min 23 s in Egypt, and in Spain, 4 min 48 s in Ceuta, the longest in the country according to the IGN (Spain’s National Geographic Institute). The whole eclipse, from the first bite to the end, lasts a little over two hours.

A lunar totality can last much longer. NASA describes a Moon that turns red over the course of a few hours. The total lunar eclipse of 31 December 2028, according to its tables, will have 1 h 11 min of totality, and we cover it in the lunar eclipses of 2028.

Which one you can look at without protection

Looking at a lunar eclipse carries no risk at all for your eyes. NASA says all its phases can be watched with the naked eye and through a telescope with no filter. What you are looking at is the Moon, which only reflects the Sun’s light.

With the Sun it’s the other way round. According to NASA, it can only be looked at without protection when the Moon covers it completely, that is, during totality; in the partial phases and in an annular eclipse it is never safe to look directly at it without proper protection. Space Place tells children never to look directly at the Sun, not even for a second, and that sunglasses won’t do, however many pairs you put on. The rule followed by the IGN and the American Astronomical Society (AAS) is an EN ISO 12312-2 filter in all the partial phases, and no filter only between the last flash and the first. Why not even a glance is safe is explained in don’t look at the partial phase without glasses, not even for a second (in Spanish), and when to take them off, in this article.

To check any pair of glasses there is our glasses guide. On Order your glasses you can ask for ours: cardboard, with the EN ISO 12312-2 certificate, along with the phone filter and packs for groups.

Why the Moon turns red and the Sun shows its corona

In a total lunar eclipse, the Moon turns reddish. Fred Espenak, the author of NASA’s eclipse tables, explains on his website EclipseWise that the Earth’s atmosphere scatters blue and green light and lets the red through, and that red light ends up lighting the Moon. The brightness varies from one eclipse to another, and it is measured on the Danjon scale, which runs from an almost invisible Moon to a very bright copper or orange one.

During the totality of a solar eclipse, once the disc is covered, the corona appears: the Sun’s outer atmosphere, which can’t be seen the rest of the time. What it is and what shape it will have is in our learn section.

Sources: Types of Solar Eclipses — NASA Science (a solar eclipse with the Moon between the Sun and the Earth; a lunar eclipse with the Earth in between, at full moon; total in the centre of the shadow and partial outside it; the Moon turning red over a few hours); Solar eclipse — Wikipedia (only at new moon near a node; totality along a narrow strip; the maximum of 7 min 32 s); Eclipses — NASA Space Place (Spanish edition: where each one can be seen from; never look at the Sun, not even for a second; sunglasses are no good); Total Lunar Eclipse: Telescopic View — NASA Scientific Visualization Studio (all phases of a lunar eclipse can be watched with the naked eye and through a telescope with no filter); Eclipse Viewing Safety — NASA Science (no protection only in totality; never in the partial phases or in an annular eclipse); Total Lunar Eclipse of 2028 Dec 31 — NASA, Fred Espenak (1 h 11 min of totality); Visual Appearance of Lunar Eclipses — EclipseWise, Fred Espenak (the red colour and the Danjon scale); durations in Spain: IGN — eclipses.ign.es (in Spanish); width of the path and maximum duration in 2027: Path of the Total Solar Eclipse of 2027 Aug 02 — NASA, Fred Espenak; eclipseando data (skyfield + DE440s engine).