Why is it cold during perihelion?
I was confused that the summers and winters in the northern and southern hemispheres occurred at opposite times of the year.
I eventually found out that our seasons are primarily due to the tilt of the Earth, resulting in the sun appearing lower in the sky during the winter thus providing less heat.
That this occurs (for us northern hemisphere dwellers) around the time of closest approach to the sun is probably coincidence and will change slowly over time in a 26000 year cycle.
Perihelion currently occurs during the northern hemisphere Winter.
Perihelion currently occurs around 3 January each year. This is in the northern hemisphere Winter.
The seasons are mainly due to the obliquity of the Earth's axis of rotation, or axial tilt.
At perihelion the Earth is about 147,000,000 km from the Sun. At aphelion it is about 152,100,000 km from the Sun. The difference is about 5,000,000 km which doesn't have a significant effect on temperatures.
Due to precession the date of perihelion gets later by about a day every 70 years. So, in about 5,600 years time, perihelion will be in the northern hemisphere Spring and it will no longer be cold at perihelion.