NJIT Physics 203 — Earth in Space, Exam 1
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1. Which of the following best describes the celestial sphere?
A) A real physical shell surrounding Earth.
B) A model where stars are projected onto an imaginary sphere around Earth.
C) The region of space occupied by our solar system.
D) The path the Sun follows through the sky.
Answer: B
Rationale: The celestial sphere is an imaginary sphere used as a coordinate system where
stars appear projected onto its inner surface.
2. The right ascension (RA) coordinate of a star is most analogous to which Earth
coordinate?
A) Latitude
B) Altitude
C) Longitude
D) Elevation
Answer: C
Rationale: Right ascension measures east–west position on the celestial sphere like
longitude on Earth.
3. Which of these is a sidereal day?
A) Time between successive solar noons.
B) Time for the Moon to orbit Earth.
C) Time it takes Earth to rotate once relative to the distant stars.
D) Time between successive sunrises.
Answer: C
Rationale: A sidereal day is Earth’s rotation period relative to distant stars (~23h56m).
,4. The ecliptic is:
A) The Moon’s orbital plane projected on the sky.
B) The Sun’s apparent path among the stars over a year.
C) The path of comets.
D) The equator of the celestial sphere.
Answer: B
Rationale: The ecliptic is the Sun’s apparent annual path against the background stars
caused by Earth’s orbit.
5. Why do we have seasons on Earth?
A) Because Earth is closer to the Sun in summer.
B) Because Earth’s axis is tilted relative to its orbital plane.
C) Because the Sun’s brightness varies throughout the year.
D) Because of the Moon’s gravitational influence.
Answer: B
Rationale: Seasons are caused by the ~23.5° tilt of Earth’s rotation axis, changing
sunlight angle and daylight length.
6. Which statement about perihelion and aphelion is correct?
A) Earth is at perihelion in June and aphelion in December.
B) Perihelion is when Earth is farthest from the Sun.
C) Perihelion is when Earth is closest to the Sun.
D) They determine the seasons.
Answer: C
Rationale: Perihelion = closest approach to the Sun; aphelion = farthest. Seasons are
primarily tilt-driven, not distance-driven.
7. A synodic month refers to:
A) Time for the Moon to rotate once on its axis.
B) Time between successive new moons as seen from Earth.
C) Time for the Moon to complete an orbit relative to the stars.
D) The time between lunar eclipses.
Answer: B
Rationale: A synodic month (~29.53 days) is the lunar phase cycle, i.e., new moon to new
moon.
8. A sidereal month refers to:
A) Time for the Moon to orbit Earth relative to the stars.
B) Time between full moons.
C) Time for the Moon to complete a phase cycle.
, D) Time for the Moon to move through the ecliptic.
Answer: A
Rationale: A sidereal month (~27.32 days) measures the Moon’s orbital period relative to
the background stars.
9. Which phase is the Moon in at first quarter?
A) New Moon
B) Full Moon
C) Half illuminated, right side lit (for Northern Hemisphere)
D) Waning crescent
Answer: C
Rationale: First quarter is when half the Moon’s disk is illuminated and the right side (as
seen from N. Hemisphere) is lit.
10. During a total solar eclipse, which body casts the shadow on Earth?
A) The Sun
B) The Moon
C) Earth
D) Venus
Answer: B
Rationale: The Moon blocks sunlight and casts its shadow on parts of Earth, producing a
solar eclipse.
11. Which condition is necessary for a solar eclipse to occur?
A) Moon must be at full phase.
B) Moon must be at new phase and near a node of its orbit.
C) Moon must be at first quarter.
D) Sun must be at perihelion.
Answer: B
Rationale: Solar eclipses require the moon to be new and close to one of the orbital
nodes so shadow falls on Earth.
12. Why don’t we have a solar eclipse every new moon?
A) Because the Moon’s orbit is tilted ~5° relative to the ecliptic.
B) Because the Sun is too small.
C) Because Earth’s atmosphere refracts sunlight.
D) Because the Moon sometimes doesn’t reflect light.
Answer: A
Rationale: The 5° orbital tilt means the Moon usually passes above or below the Sun in
the sky except near nodes.
Questions And Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A | Instant
Download Pdf
1. Which of the following best describes the celestial sphere?
A) A real physical shell surrounding Earth.
B) A model where stars are projected onto an imaginary sphere around Earth.
C) The region of space occupied by our solar system.
D) The path the Sun follows through the sky.
Answer: B
Rationale: The celestial sphere is an imaginary sphere used as a coordinate system where
stars appear projected onto its inner surface.
2. The right ascension (RA) coordinate of a star is most analogous to which Earth
coordinate?
A) Latitude
B) Altitude
C) Longitude
D) Elevation
Answer: C
Rationale: Right ascension measures east–west position on the celestial sphere like
longitude on Earth.
3. Which of these is a sidereal day?
A) Time between successive solar noons.
B) Time for the Moon to orbit Earth.
C) Time it takes Earth to rotate once relative to the distant stars.
D) Time between successive sunrises.
Answer: C
Rationale: A sidereal day is Earth’s rotation period relative to distant stars (~23h56m).
,4. The ecliptic is:
A) The Moon’s orbital plane projected on the sky.
B) The Sun’s apparent path among the stars over a year.
C) The path of comets.
D) The equator of the celestial sphere.
Answer: B
Rationale: The ecliptic is the Sun’s apparent annual path against the background stars
caused by Earth’s orbit.
5. Why do we have seasons on Earth?
A) Because Earth is closer to the Sun in summer.
B) Because Earth’s axis is tilted relative to its orbital plane.
C) Because the Sun’s brightness varies throughout the year.
D) Because of the Moon’s gravitational influence.
Answer: B
Rationale: Seasons are caused by the ~23.5° tilt of Earth’s rotation axis, changing
sunlight angle and daylight length.
6. Which statement about perihelion and aphelion is correct?
A) Earth is at perihelion in June and aphelion in December.
B) Perihelion is when Earth is farthest from the Sun.
C) Perihelion is when Earth is closest to the Sun.
D) They determine the seasons.
Answer: C
Rationale: Perihelion = closest approach to the Sun; aphelion = farthest. Seasons are
primarily tilt-driven, not distance-driven.
7. A synodic month refers to:
A) Time for the Moon to rotate once on its axis.
B) Time between successive new moons as seen from Earth.
C) Time for the Moon to complete an orbit relative to the stars.
D) The time between lunar eclipses.
Answer: B
Rationale: A synodic month (~29.53 days) is the lunar phase cycle, i.e., new moon to new
moon.
8. A sidereal month refers to:
A) Time for the Moon to orbit Earth relative to the stars.
B) Time between full moons.
C) Time for the Moon to complete a phase cycle.
, D) Time for the Moon to move through the ecliptic.
Answer: A
Rationale: A sidereal month (~27.32 days) measures the Moon’s orbital period relative to
the background stars.
9. Which phase is the Moon in at first quarter?
A) New Moon
B) Full Moon
C) Half illuminated, right side lit (for Northern Hemisphere)
D) Waning crescent
Answer: C
Rationale: First quarter is when half the Moon’s disk is illuminated and the right side (as
seen from N. Hemisphere) is lit.
10. During a total solar eclipse, which body casts the shadow on Earth?
A) The Sun
B) The Moon
C) Earth
D) Venus
Answer: B
Rationale: The Moon blocks sunlight and casts its shadow on parts of Earth, producing a
solar eclipse.
11. Which condition is necessary for a solar eclipse to occur?
A) Moon must be at full phase.
B) Moon must be at new phase and near a node of its orbit.
C) Moon must be at first quarter.
D) Sun must be at perihelion.
Answer: B
Rationale: Solar eclipses require the moon to be new and close to one of the orbital
nodes so shadow falls on Earth.
12. Why don’t we have a solar eclipse every new moon?
A) Because the Moon’s orbit is tilted ~5° relative to the ecliptic.
B) Because the Sun is too small.
C) Because Earth’s atmosphere refracts sunlight.
D) Because the Moon sometimes doesn’t reflect light.
Answer: A
Rationale: The 5° orbital tilt means the Moon usually passes above or below the Sun in
the sky except near nodes.
