The total moon eclipse of September 7, 2025 – Paris Observatory – PSL

To know the details of what you can observe according to your location, you can go to the site ssp.imcce.fr and choose your location to obtain what is called local circumstances.

Here are those of Paris for example:

As you can read, from Paris, observers will not see the start of the eclipse, or the beginning of the whole. The moon will only be visible after the maximum of the eclipse when it rises to the east.

Here are the general circumstances of the eclipse:

What will be the possibilities of observation in other places?

• The eclipse will be visible in whole on all the territories of the Indian Ocean (Mauritius, Reunion, Seychelles, Maldives and French Southern and Antarctic Lands).
• In New Caledonia, the eclipse will be visible in the second half of the night (September 7 or 8). The first phases of the eclipse as well as the entire phase will be observable. The moon will then go to the west during the second phase.
• In Tahiti, only the very beginning of the phase by the darkness will be possibly visible but almost unobservable.
• The entire phase will also be fully visible since: Asia, the Indian Ocean. It will only be partly visible from the Atlantic Ocean, Europe, Africa, the West Pacific Ocean, Australia.

Visibility card of the total moon eclipse of September 7, 2025. LTE credits

The above card is centered on the visibility area. On each side are two invisibility areas. For total moon eclipses, 6 curves are traced:

1. Entrance into the dark (P1): moment of the first external contact with the half -light cone (large dotted lines).
2. Entrance into the shade (O1): Instant of the first external contact with the shadow cone (small dotted lines).
3. Beginning of the whole (T1): Instant of the first inner contact with the shadow cone (full line).
4. End of the whole (T2): Instant of the last inner contact with the shadow cone (full line).
5. Out of the shadows (O2): Instant of the last external contact with the shadow cone (small dotted lines).
6. Exit of the dark (P2): Instant of the last external contact with the half -light cone (large dotted lines).

Each of these curves corresponds to the places where the moon is on the horizon at the moment of the corresponding phase: the curves in red correspond to the places where the moon rises and the curves in blue to those where the moon sets.

For each phase, the places located west of a red curve do not see the phase, because the moon is not yet lifted, while those located in the east see it, because the moon is already lifted.

Likewise, the places located east of a blue curve do not see the phase, because the moon is already lying, while those located to the west see it, because the moon is not yet lying.

What can we see in the case of a total moon eclipse?

During the phenomenon, the Moon gradually escapes the lighting of the sun, so that at the maximum of the eclipse, when the moon is as close as possible to the center of the shadow cone, the amount of light it receives from the sun decreases considerably. It increases again little after the maximum.

During a total eclipse, during the entire phase, the moon is inscribed inside the shadow cone projected by the earth in space and takes a more or less intense coppery shade. This light comes from the solar radiation deflected towards the interior of the shadow during its crossing of the earth’s atmosphere. By the way, light is also dispersed, a phenomenon which mainly affects blue components, and therefore suggests the red components. This is the reason why the moon still appears to us visible, simply tinged with red.

What are the conditions for a eclipse to take place?

An eclipse of the moon occurs when the moon passes in the shadow of the earth, which is then interposed between the sun and the moon, blocking all or part of the solar radiation which comes to light the moon.

For a moon eclipse to take place, the moon must be in opposition to the sun vis-à-vis the earth, that is to say in the full moon phase, and that it is close to one of the nodes of its orbit. In a geocentric benchmark, the nodes correspond to the intersections of the plane of the orbit of the moon with the plane of the orbit of the sun, called ecliptic, because it is when the moon goes through this plan that it can occur from eclipses, sun and moon.

Representation of the line of lunar nodes. Credits Y. Gominet/LTE

To see the different phases of a moon eclipse in a given place, it is enough that it is dark during these phases. Indeed, moon eclipses always occur at the full moon. Now at the full moon, the moon rises when the sun sets and sets when the sun rises: the moon is therefore visible all night.

Occultations, eclipses, passages: interactive module to understand these phenomena.

What factors depends on the duration of an eclipse?

• From the positioning of the moon compared to the center of the shadow: the closer the moon is the center of the shadow at the time of the maximum, the longer the eclipse lasts.
• From the Terre-Moon distance: the lunar orbit is an ellipse (and not a circle), therefore this distance varies constantly. When the moon is in its position farther from the earth (at its peak), it appears smaller in the sky and also moves more slowly along its orbit, so that it ultimately puts more time to cross the shadow cone. On the contrary, when the moon is in its position closest to the earth (at its perigee), it will appear greater in the sky, and will advance more quickly on its orbit.

Legend High Image of the article: The total moon eclipse of January 21, 2019. Credits J. Normand