Earth too close to the Sun?


On Saturday, January 2nd, 2010, the Earth was only 147,098,000 kilometers away from the Sun. But don’t worry. Earth is not spiraling down to the Sun for an eventual collision. This is an annually recurring event known as perihelion.

Earth perihelion occurs every year in early January, and marks the minimum distance between Sun and Earth for the year. There are two related concepts worthy of discussion around this time.

1) Earth does not orbit the Sun in a perfectly circular orbit. In fact, no planet does. Planets (and moons, comets, asteroids, artificial satellites and anything else) orbit in ellipses. This was theorized by Johannes Kepler 400 years ago, and is now known as Kepler’s first law of orbital dynamics. An elliptical orbit has two focal points. The Sun is one of the focal points for planetary orbits; the other is a mathematically calculated point in space, but there is no physical object there.

The measurement of this non-circularity is called eccentricity, and varies between 0 (a perfect circle) and 1 (an infinitely elongated ellipse–essentially a flat line). Earth’s eccentricity is 0.0167–a very small number. Venus and Neptune has the most circular orbits in the solar system (e=0.0068 and 0.0095 respectively). Pluto’s eccentricity is 0.249–very high for a planet.

Pluto’s high eccentricity was a significant factor in the decades-long debate as to whether or not it should be considered a planet. Ironically, when the IAU (International Astronomical Union) decided on the definition of a major planet, back in 2006, eccentricity wasn’t part of the final definition, which reclassified Pluto as a ‘dwarf planet.’

2) Seasonal changes are not due to the changing distance between Sun and Earth. Seasons are the result of the tilt of the Earth’s axis relative to its orbital plane. Even though we are at perihelion in early January, there is a minimal effect on temperatures and weather systems.

Earth will be at aphelion, or its furthest distance from the Sun, 0n July 6th, 2010. The distance between the two at that time will be 152,096,500 km.

8 thoughts on “Earth too close to the Sun?

  1. On saturday January 2, 2010 at 10:37 P.M. I saw what appeared to be a meteor (or could have been space junk) come across the northern utah sky while driving up I-15 just north of Centerville. I was unable to find anything on the web do you or have you heard anything about that night?

  2. The IAU’s controversial planet definition is not likely to last and is already rejected by many astronomers. Only four percent of the IAU voted on the controversial demotion, and most are not planetary scientists. Their decision was immediately opposed in a formal petition by hundreds of professional astronomers led by Dr. Alan Stern, Principal Investigator of NASA’s New Horizons mission to Pluto. One reason the IAU definition makes no sense is it says dwarf planets are not planets at all! That is like saying a grizzly bear is not a bear, and it is inconsistent with the use of the term “dwarf” in astronomy, where dwarf stars are still stars, and dwarf galaxies are still galaxies. Also, the IAU definition classifies objects solely by where they are while ignoring what they are. If Earth were in Pluto’s orbit, according to the IAU definition, it would not be a planet either. A definition that takes the same object and makes it a planet in one location and not a planet in another is essentially useless. Pluto is a planet because it is spherical, meaning it is large enough to be pulled into a round shape by its own gravity–a state known as hydrostatic equilibrium and characteristic of planets, not of shapeless asteroids held together by chemical bonds. These reasons are why many astronomers, lay people, and educators are either ignoring the demotion entirely or working to get it overturned.

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