UPCAT General Science (Extended) — Astronomy & the PlanetsFlash Cards

What makes blue stars different from red stars in terms of temperature?

Blue stars are the hottest with surface temperatures above 37,000°F, while red stars are the coolest with temperatures below 5,500°F. Yellow stars like our Sun are in between at about 10,000°F. The color directly indicates the star's surface temperature - hotter stars appear blue, cooler stars appear red.

A comet is approaching the Sun. What will happen to its appearance and why?

The comet will develop a visible tail as it gets closer to the Sun. Comets are 'dirty snowballs' of frozen gases, rock, and dust. Solar radiation heats and vaporizes the ice, creating jets of gas and dust that form the characteristic tail pointing away from the Sun.

Why can we see more stars during a new moon compared to a full moon?

During a new moon, there's no moonlight to create light pollution in the sky, making fainter stars visible. During a full moon, the bright reflected sunlight from the Moon's surface creates a natural light pollution that washes out dimmer stars, reducing visibility of celestial objects.

What is the difference between a meteoroid, meteor, and meteorite?

A meteoroid is a small rock or particle in space. A meteor is the bright streak of light (shooting star) when a meteoroid burns up in Earth's atmosphere. A meteorite is the remaining piece that actually hits Earth's surface. Think: space rock → burning streak → ground impact.

How do we know that planets orbit in elliptical rather than circular paths?

Johannes Kepler discovered this through careful observation of planetary motion, particularly Mars. His First Law states that planets orbit the Sun in elliptical paths with the Sun at one focus. This explains why planets sometimes appear closer or farther from the Sun during their orbits.

Why does Jupiter have so many moons (67) compared to Earth (1)?

Jupiter has much stronger gravity due to its massive size (318 times Earth's mass). This strong gravitational field can capture and hold many objects in orbit. Additionally, Jupiter formed in the outer solar system where there was more material available to form moons.

What happens inside the Sun's core to produce energy?

Nuclear fusion occurs in the Sun's core, where hydrogen atoms combine to form helium at temperatures of about 15 million°C. This process converts a small amount of mass into enormous amounts of energy (following E=mc²), which eventually reaches us as sunlight and heat.

Why do we always see the same side of the Moon from Earth?

The Moon's rotation period (27.3 days) equals its orbital period around Earth. This phenomenon is called synchronous rotation or tidal locking. The Moon rotates once on its axis in exactly the same time it takes to complete one orbit around Earth, keeping the same face toward us.

During a solar eclipse, what is the correct alignment of celestial bodies?

Sun → Moon → Earth. The Moon passes between the Sun and Earth, casting its shadow on Earth. This can only happen during a new moon phase when the three bodies are aligned. The Moon blocks sunlight from reaching parts of Earth, creating the eclipse.

What is a supernova and what happens after one occurs?

A supernova is an extremely large exploding star that occurs when a massive star runs out of nuclear fuel. After the explosion, the remaining core may form a neutron star (very dense) or collapse completely into a black hole if the mass is sufficient.

Why is Venus hotter than Mercury even though Mercury is closer to the Sun?

Venus has a thick atmosphere composed mainly of carbon dioxide, creating an extreme greenhouse effect that traps heat. Surface temperature reaches 740K (467°C). Mercury has almost no atmosphere to retain heat, so despite being closer to the Sun, it cannot maintain as high temperatures as Venus.

What causes the different phases of the Moon?

Moon phases result from changing positions of the Sun, Earth, and Moon. As the Moon orbits Earth, different portions of its sunlit side become visible from Earth. New moon (not visible) → Waxing crescent → First quarter → Waxing gibbous → Full moon → Waning gibbous → Last quarter → Waning crescent.

According to Kepler's Second Law, when does a planet move fastest in its orbit?

A planet moves fastest when it is closest to the Sun (perihelion). Kepler's Second Law states that planets sweep out equal areas in equal time periods, so when closer to the Sun, the planet must move faster to cover the same area as when it's farther away.

What makes Saturn unique among all planets in our solar system?

Saturn has the lowest density of all planets (0.70 g/cm³), less dense than water. It also has the most prominent ring system. If you could find an ocean large enough, Saturn would float! This low density is due to its composition of mostly hydrogen and helium gases.

How do astronomers determine the composition of distant stars?

Through spectroscopy - analyzing the light from stars. Different elements absorb and emit specific wavelengths of light, creating unique 'fingerprints' or spectral lines. By studying these patterns in starlight, astronomers can identify what elements are present in the star's atmosphere.

Why do gas giants like Jupiter and Saturn have many moons while rocky planets have few?

Gas giants formed in the outer solar system where more material was available and their massive size creates stronger gravitational fields that can capture objects. Rocky planets formed in the inner solar system with less available material and weaker gravity, limiting their ability to capture and retain moons.

What is the asteroid belt and where is it located?

The asteroid belt is a region between Mars and Jupiter containing thousands of rocky objects called asteroids or minor planets. These are leftover materials from the solar system's formation that never formed into a planet, likely due to Jupiter's strong gravitational influence preventing their accumulation.

How does the Sun's chromosphere differ from its photosphere?

The photosphere is the Sun's visible surface where sunlight originates, appearing yellow-white. The chromosphere is the lower atmosphere above the photosphere, appearing bright red during solar eclipses due to hydrogen emissions. The chromosphere is hotter than the photosphere despite being farther from the core.

Why was Pluto reclassified from a planet to a dwarf planet?

Pluto doesn't meet the third criterion for being a planet: it hasn't 'cleared its orbit' of other objects. Pluto shares its orbital space with many other objects in the Kuiper Belt. While it orbits the Sun and is roughly spherical, its inability to gravitationally dominate its orbital neighborhood led to its reclassification in 2006.

What is the significance of the Copernican model over the Ptolemaic model?

Copernicus proposed the heliocentric model (Sun-centered) which correctly placed the Sun at the center with planets orbiting around it. This was revolutionary compared to Ptolemy's geocentric model (Earth-centered) which required complex 'epicycles' to explain planetary motion. The Copernican model was simpler and more accurate.