The NASA GLOBE Clouds team at NASA Langley Research Center is working with NASA scientist Dr. Bill Smith to use GLOBE Cloud observations made by people just like you to solve the Terminator Problem!

Wait, what? Well, the Solar Terminator or twilight zone is that line that separates the daylit side of a planet from the dark night side. The image on the left is an example. It was taken from the International Space Station as it crossed the terminator on April 17, 2019 as it orbits 254 miles above the Gulf of Guinea on Africa’s mid-western coast. 



How can you help?

You can take cloud observations during dusk and dawn. We ask that when you submit your photographs, you add the comment “terminator” on the caption space to at least one of the photos using the GLOBE Observer app (learn how to get the app). The comment will alert the team that we have received an observation during this specific time. This short video walks you through how to take a cloud observation using the GLOBE Observer app.

GLOBE Program educators, if you are using the GLOBE Data Entry form, you can add the comment “terminator” in the comment box at the bottom of the data submission page.

When should I take the observation?

If you would like to help the team with the terminator problem, we ask that you take a cloud observation when the sun is about 10 degrees above the horizon or lower. 



You can measure this in different ways:

  1. Check the sunrise or sunset times for your area (here is an example website Then, go outside and take a cloud observation within an hour of that time  (an hour before if observing a sunset, and up to an hour later if observing a sunrise). 

  2. The horizon is at zero degrees, and directly overhead is ninety degrees. If you hold your fist at arm's length and place your fist resting on the horizon, the top will be at approximately 10 degrees.  If the Sun appears at approximately that height or below, you can take a “terminator” observation.

  3. Use the photographs portion GLOBE Observer app. The app asks you to put a letter in a circle found in each cardinal direction. This circle is at about 14 degrees above the horizon. If the sun is lower than the circle found in the photographs portion of the app, then you are close to the terminator region.

How to add a comment to a photograph using the GLOBE Observer app?

Follow the steps to take the photographs using the GLOBE Observer app. Click “done” when you have finished taking all six photographs. Turn your phone vertically or up and down. As you review the photographs, notice the comment box under each photograph. Click on at least one of the comment boxes and add the word terminator

This summer the NASA GLOBE Clouds team will select an intern through the NASA’s Internships, Fellowships, and Scholarships (or NIFS) program to analyze your observations and compare them to GOES data! Find out more about this and similar opportunities at .

More Blog Entries