- If the Earth is closest to the Sun in January (perihelion), why isn't it summer in the Northern Hemisphere then?
- The variation in Earth-Sun distance due to orbital eccentricity is minor compared to the effect of axial tilt. Seasons are driven primarily by the solar altitude, which controls the concentration of solar energy on a surface. In January, the Northern Hemisphere is tilted away from the Sun, resulting in low solar altitude and short days, despite being slightly closer. The axial tilt effect overwhelms the small variation in distance.
- Does the simulator show why days are longer in summer?
- Indirectly, yes. The solar altitude plot shows the sun's position at noon, its highest point. The simulator's declination model is key: when the Sun's declination matches your hemisphere's latitude (e.g., +23.4° in June for the Northern Hemisphere), the Sun is higher and its daily arc across the sky is longer, leading to more daylight hours. The exact sunrise/sunset times require a more complex calculation involving the observer's latitude and the Sun's declination.
- Why is the solar declination curve not a perfect sine wave?
- The model here uses a perfect sine wave for simplicity, which is a very good approximation. In reality, the curve has slight asymmetries due to Earth's elliptical orbit (Kepler's Second Law), meaning Earth moves faster at perihelion. This causes the seasons to have slightly unequal lengths. The more accurate representation of the Sun's position throughout the year, incorporating this and other factors, is a figure-8 pattern called the analemma.
- Can I use this model to find the Sun's noon altitude for my exact location on a specific date?
- Yes, with two important notes. First, ensure you use your latitude correctly (positive for north, negative for south). Second, the model uses a standard calendar and declination formula; for a precise calculation on a specific date, you would need the exact astronomical declination. However, for educational purposes and understanding seasonal trends, this simulator provides an excellent and accurate estimation.