Grade 4 Reading — Science & Space

Phases of the Moon

The Moon does not produce its own light. Instead, it reflects sunlight like a bright disk in the night sky. As the Moon orbits Earth, we see different portions of its sunlit side. These changing shapes are called phases. Understanding phases helped early sailors and farmers plan their work long before modern calendars existed. A new moon occurs when the Moon sits between Earth and the Sun. The side facing us is in shadow, so the Moon seems to vanish from view. Within a few days, a thin curve called a crescent appears low in the evening sky. The lit portion grows larger each night until half the Moon is visible. When the entire face we can see is illuminated, we call it a full moon. After a full moon, the bright section shrinks again. The cycle from new moon to full moon and back takes about twenty-nine days. Some cultures named each full moon after seasonal events, such as harvest time…

Robots Exploring Mars

Mars is often called the Red Planet because iron-rich dust gives its surface a rusty color. It is farther from the Sun than Earth, so temperatures there are colder and the atmosphere is thin. Still, scientists wonder whether Mars once held lakes or even tiny forms of life. To find answers, space agencies have sent robotic rovers to explore the planet's rocky deserts. A rover is a mobile laboratory on wheels. Engineers design it to survive harsh dust storms, extreme cold, and rough terrain. Solar panels or nuclear batteries supply power. Cameras capture panoramic views, while robotic arms collect soil and rock samples. Onboard instruments analyze minerals and search for signs of ancient water. Because radio signals take many minutes to travel between Earth and Mars, rovers cannot be driven like remote-control cars. Scientists upload a list of commands. The rover executes them carefully,…