OBA Practice Questions - 29a Olimpíada Brasileira de Astronomia e Astronáutica - 2026 Exam - OBA Practice Questions - 29a Olimpíada Brasileira de Astronomia e Astronáutica

Question 1

What is the primary astronomical cause of the annual cycle of seasons on Earth?

The constant 23.44° tilt of Earth's rotational axis relative to the ecliptic plane as it revolves around the Sun The periodic variation in distance between the Earth and the Sun due to Earth's orbital eccentricity (perihelion vs aphelion) The periodic fluctuation in the Sun's total solar irradiance and magnetic activity over an 11-year cycle The gravitational precession of Earth's rotational axis relative to the background constellations

Correct Answer:

The constant 23.44° tilt of Earth's rotational axis relative to the ecliptic plane as it revolves around the Sun

Question 2

A solar day on Earth lasts exactly 24 hours (86,400 seconds), whereas a sidereal day lasts approximately 23 hours, 56 minutes, and 4 seconds. What explains this 3 minute and 56 second difference?

Atmospheric refraction delays the perceived setting of the Sun relative to distant background stars Earth advances approximately 1° along its orbit around the Sun each day, requiring an extra ~4 minutes of rotation to realign with the Sun Tidal braking from the Moon's gravitational pull slows down Earth's rotation during daylight hours Earth's orbital velocity increases as it moves from aphelion to perihelion according to Kepler's second law

Correct Answer:

Earth advances approximately 1° along its orbit around the Sun each day, requiring an extra ~4 minutes of rotation to realign with the Sun

Question 3

During an equinox, what approximate solar pattern is observed at locations away from the geographic poles when atmospheric refraction is ignored?

The Sun reaches its maximum altitude of exactly 90° (zenith) at solar noon from every latitude on Earth The Sun remains continuously above the horizon for 24 hours at both the North and South geographic poles The Sun rises due east and sets due west, with day and night each lasting approximately 12 hours The shadow cast by a vertical gnomon at local solar noon completely disappears across the entire Southern Hemisphere

Correct Answer:

The Sun rises due east and sets due west, with day and night each lasting approximately 12 hours

Question 4

The city of São Paulo has a geographic latitude of approximately 23°33' S. How many times per year does the Sun reach the exact zenith (altitude 90°) at solar noon in São Paulo?

Twice per year, once in late spring and once in late summer Once per year, precisely at the December summer solstice Four times per year, during the equinoxes and cross-quarter days Zero times per year, because São Paulo lies south of the Tropic of Capricorn (23°26' S)

Correct Answer:

Zero times per year, because São Paulo lies south of the Tropic of Capricorn (23°26' S)

Question 5

What physical mechanism causes the precession of the equinoxes, which has a cycle period of approximately 25,772 years?

Gravitational torque exerted by the Moon and the Sun on Earth's equatorial oblateness (bulge) Magnetic torque generated by the interaction between the solar wind and Earth's liquid outer core dynamo Relativistic frame dragging of spacetime caused by the rapid rotation of the Sun Tidal friction between the oceanic water masses and the ocean floor shifting Earth's center of mass

Correct Answer:

Gravitational torque exerted by the Moon and the Sun on Earth's equatorial oblateness (bulge)

Question 1

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Prepare with the OBA Practice Questions - 29a Olimpíada Brasileira de Astronomia e Astronáutica - 2026 Exam practice quiz. This question bank includes 100 questions covering star, solar, earth, approximately, and planet. Use it to review important concepts, identify knowledge gaps, and build confidence for the related exam, course, or assessment.

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OBA Practice Questions - 29a Olimpíada Brasileira de Astronomia e Astronáutica - 2026 Exam

This practice set contains 100 questions from the matching question bank and focuses on star, solar, earth, approximately, and planet. Work through each question carefully, review the provided solutions, and revisit topics that need more study before your next attempt.

This is an independent study resource intended for practice and review; it is not an official examination or an endorsement by any organization named in the title.

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OBA Practice Questions - 29a Olimpíada Brasileira de Astronomia e Astronáutica - 2026 Exam

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