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Does the Nile Delta change?

Data as of 2026-10-15

Pupils compare two editions of the same satellite mosaic over the same place, west of Cairo, and learn to tell what a satellite observed from what the scene only computes.

At a glance

Subjects
geography, Earth science
Age range
12 to 16 years old
Difficulty
medium
Lesson time
45 minutes
Material
  • A computer or tablet per group, with a recent web browser (the scene uses WebGL).
  • An internet connection: the satellite images are streamed while the scene runs.
  • The printed pupil sheet below.
Scene to open
The Nile Delta through time

Learning objectives

Teacher guide and answer key

1. Predict, then look

Ask the class what can change in a landscape between two satellite images: a river, a coast, a field, a city. Have them write a prediction for the Nile Delta, a green fan in the middle of the desert. Then start the tour: it shows the whole delta with one edition of a satellite mosaic, then zooms on the western edge of Cairo.

Answer key

Which edition of the images is shown at the first step, and from which months are the images made?
The 2016 edition of the Sentinel-2 cloudless mosaic, made of images taken from January 2016 to December 2017. A mosaic is built from images taken over those months: it does not show one day.

2. Compare two dates

The tour then frames Cairo in the first edition, jumps to the second edition and frames the same place again: only the date, and the edition that goes with it, change. Let the pupils look at the left of the image, the desert west of the city, before and after. The second question prepares the last part: the two editions do not have the same tone, which is visible on screen.

Answer key

What has appeared west of Cairo between the two images?
Many round fields appear in the desert west of the city; the first image shows almost none. The second image is the 2025 edition, made of images taken from January 2025 to December 2025.
Why should you compare the shapes in the two images, and not their colours?
The two editions do not have the same tone: the 2025 image is darker overall. A difference of tone alone therefore proves nothing about the land. A new shape, such as a field or a road, does.
To go further, advanced: Can you say in which year the round fields appeared? Explain.
No. Each edition describes a span of months, January 2016 to December 2017 for the first and January 2025 to December 2025 for the second. Two editions give a before and an after, not the date of the change, which happened at some point between them.

3. Observed or calculated?

The last text jumps to a date no satellite has seen yet. The image stays the latest edition and the banner says so, while the lighting follows the computed position of the Sun. This is the habit to keep: always ask whether what is on screen was observed, or calculated.

Answer key

A pupil says: “the last image is a satellite photo of the future”. Is that right?
No. No satellite has seen that date: the image is still the 2025 edition, whose images end in December 2025, and the banner says so. What the date changes is computed, not observed: the position of the Sun, taken from the ephemerides, and so the lighting.
To go further, upper secondary: A classmate says: “the round fields prove that the land is now irrigated”. What can the image prove, and what would you need to check somewhere else?
The image proves a shape: round fields exist in the edition made of images from January 2025 to December 2025, and almost none in the first one. It does not give the cause. For that you need another source, such as a farming or water-use record. Telling what is observed from what is concluded is the first rule of reading a satellite image.

Image dates quoted from the product sheets of the imagery editions, not computed. Sources:

Pupil sheet

Does the Nile Delta change?

Address of the scene: https://galaxy.adrianguichard.dev/earth/?tour=nile-delta

1. Predict, then look

  1. Open the address of the scene, written above. Read the first text, then look at the banner at the bottom of the screen.
  2. Write down which edition of the images is shown, and the months the banner gives for them.

Which edition of the images is shown at the first step, and from which months are the images made?

2. Compare two dates

  1. At the second text (Cairo, still in the first edition), look at the left of the image, the desert west of the city. Describe or draw what you see: fields, roads, buildings.
  2. Go to the next text. The camera does not move: only the date changes, and the edition with it. Describe or draw what is different.

What has appeared west of Cairo between the two images?

Why should you compare the shapes in the two images, and not their colours?

To go further, advanced: Can you say in which year the round fields appeared? Explain.

3. Observed or calculated?

  1. Go to the last text. Read it and the banner, then note what changed on the screen and what did not.

A pupil says: “the last image is a satellite photo of the future”. Is that right?

To go further, upper secondary: A classmate says: “the round fields prove that the land is now irrigated”. What can the image prove, and what would you need to check somewhere else?

Format of this sheet

The layout follows ESA’s “teach with space” sheets, which the ESERO network relays to teachers. Reference read on October 18, 2026: ESA Education, One year on Earth: Understanding seasons (teach with space, PR45).

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