Two people, one in the Brazilian city of Manaus (near the equator) and one in New York City (near 40 degrees north latitude), observe the Sun at noon on March 21. The panels below show how these observers might see the Sun’s location (both use the same scale). Which of these choices might correctly describe these observations?

Question

BlackTom AI · Accepted Answer

At the equinox the Sun lies on the celestial equator (declination = 0°), so the solar noon altitude above the horizon is simply 90° − (observer’s latitude) for observers in the Northern Hemisphere, and about 90° − |latitude| for locations near the equator.

Step-by-step reasoning and calculations:
1. Relevant concept: solar noon altitude on the equinox = 90° − latitude (when latitude is measured north of the equator). The Sun also lies due south at local noon for observers in the Northern Hemisphere.
2. For New York City (≈ 40° N): altitude = 90° − 40° = 50°. So an observer in NYC at noon on March 21 sees the Sun about 50° above the southern horizon (well above the horizon but not overhead).
3. For Manaus (near the equator, latitude ≈ 0°; actually about 3° S but “near the equator” gives altitude ≈ 90°): altitude ≈ 90° − 0° = 90°. An equatorial observer at the equinox sees the Sun nearly at the zenith (directly overhead). If the city is slightly south of the equator, the Sun at that moment will be very near the zenith and slightly to the north; if slightly north, slightly to the south — in any case it will be very high in the sky.
4. Compare to the panels: Panel 1 shows the Sun almost overhead (very high in the sky), matching Manaus. Panel 2 shows the Sun well above the horizon but not overhead and positioned toward the southern horizon, matching NYC’s ≈50° altitude and southern direction.

Why the other choices are incorrect:
- Claiming Panel 1 is seen by both observers contradicts the large altitude difference expected between equator and 40°N.
- Claiming Panel 2 is seen by Manaus would place the Sun much lower than physically expected at the equator on the equinox.
- Reversing Panel assignments would place NYC’s Sun nearly overhead, which is wrong for 40°N on March 21.

Therefore, Panel 1 corresponds to Manaus and Panel 2 to New York City, which matches the provided correct answer.

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