Tonight
– that is, before dawn tomorrow from our North American longitudes – our planet
Earth will reach perihelion, its closest point to the sun for the year. This
annual event will take place on January 4, 2015 at 6:36 UTC (01:36 a.m. EST).
The word perihelion is from Greek roots peri meaning near, and helios meaning
sun.
Earth
is closest to the sun every year in early January, when it’s winter for the
Northern Hemisphere. We’re farthest away from the sun in early July, during our
Northern Hemisphere summer.
Earth
is about 5 million kilometers – or 3 million miles – closer to the sun in early
January than it will be in early July. That’s not a huge change in distance.
It’s not enough of a change to cause the seasons on Earth.
Despite
what many may think, Earth’s distance from the sun isn’t what causes the
seasons. On Earth, because our orbit is so close to being circular, it’s mostly
the tilt of our world’s axis that creates winter and summer. In winter, your
part of Earth is tilted away from the sun. In summer, your part of Earth is
tilted toward the sun. The day of maximum tilt toward or away from the sun is
the December or June solstice.
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