Blog

In Ptolemy’s geocentric model of the solar system, small circular loops called epicycles were attached to planetary orbits. What observed phenomenon were epicycles designed to explain?

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?

The diagram below shows electrons transitioning between energy levels in an atom, each absorbing a photon. Which transition absorbs the photon with the least energy?

White dwarfs are stable stellar remnants under most conditions. Under what circumstances can a white dwarf explode as a supernova?

Some properties of a star change depending on the observer’s distance, while others remain constant. Which property of a star would remain unchanged if observed from twice the current distance?

Modern cosmological models indicate that the total energy content of the universe is dominated by dark energy. Approximately what percentage of the universe’s total energy does dark energy account for?

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

An observer in St. Petersburg, Russia (latitude 59°56′N, longitude 30°19′E) wants to find the North Star. How would they locate Polaris from this position?

Hydrogen and helium are the most abundant elements in the universe, but heavier elements also exist. Where were elements heavier than hydrogen and helium created?