Sun and Earth Perihelion and aphelion
Perihelion and aphelion
When Earth is closest to the Sun, the north is in winter
Earth’s orbit is not a circle: the distance to the Sun varies by about five million kilometres.
- Perihelion
- Early January
- Perihelion distance
- About 147.1 million km
- Aphelion
- Early July
01 / Overview
Meet Perihelion and aphelion
Earth passes perihelion in early January at about 147.1 million km, and reaches aphelion in early July at about 152.1 million km. The 3.3% difference changes the Sun’s apparent size and the sunlight Earth receives — but it is not what causes the seasons.
How much the distance matters
Irradiance falls with the square of distance, so perihelion delivers about 6.8% more than aphelion. The tilt does far more: between the northern summer and winter solstices, the noon Sun can differ in altitude by 47°. That contrast is the direct evidence that the seasons follow the tilt, not the distance.
The northern winter half-year is shorter
By Kepler’s second law Earth moves faster near perihelion. Reckoned for the northern hemisphere, autumn equinox to spring equinox spans about 179 days, while spring to autumn spans about 186 — so the northern winter half-year is roughly a week shorter than the summer one.
02 / Key data
Core parameters
- Perihelion
- Early January
- Perihelion distance
- About 147.1 million km
- Aphelion
- Early July
- Aphelion distance
- About 152.1 million km
- Recurrence
- Once each per year
Data and calculation notes
Active periods, peak dates and rates are multi-year averages; each year differs a little, so plan against the forecast issued for the year in question.
03 / Observing tips
How to watch
- One solar image in January and one in July, with the same gear, compares the apparent diameters.
- Observing the Sun always requires a dedicated filter. No exceptions.
- This much change in distance produces no perceptible difference in temperature.
04 / Sources