Elliptical galaxies are classified on a scale from E0 to E7 based on their apparent shape. Which class appears most spherical?

Looking up at the night sky with the naked eye, some stars appear much brighter than others. Which of the following stars has the greatest apparent brightness as seen from Earth?

Earth experiences distinct seasons throughout the year. What is the primary cause of Earth’s seasons?

How do astronomers know that hydrogen gas is present in Emission nebulae?

As the director of a national astronomy funding agency, you can afford to build only one new telescope. Which of the four proposed telescopes below would provide the greatest scientific value?

The outer gas giant planets — Uranus and Neptune in particular — appear distinctly bluish in color. What causes this blue appearance?

The universe has been cooling since the Big Bang. What is the current temperature of the universe, as measured from the cosmic microwave background?

The parallax angle of a star is used to measure its distance. Which of the following changes would cause the measured parallax angle of a star to increase?

Why can’t S waves travel through Earth’s liquid core?

Figure 1What does the arrow in the above image (Figure 1) represent?