New Year astronomy January 04 2015, 0 Comments

Late January 3rd (Mountain and Pacific Time zones) or early January 4th (Eastern and Central time zones) the Earth passed through its perihelion, the point in its orbit that it is closest to the Sun. I was looking for information about Earth’s perihelion, and I was surprised to find that the day of perihelion and the actual distance the Earth is from the Sun vary quite a bit. The day falls anywhere from January 2 to January 5. The actual distance from the Sun varies by about 21,000 km, which is about 1 2/3 the Earth’s diameter.

It seems that our Moon and, to a small extent, our neighboring planets cause the Earth’s orbit to vary a little bit. While 21,000 km (about 13,000 miles) may not seem like a short distance, compare it to the average diameter of the Earth’s orbit, 149,600,000 km or 93,000,000 miles. The point of me telling you this is not to shower you with numbers, but rather to help you see in your imagination that the Earth moves in a slightly variable path, not a perfectly stable ellipse.

Another astronomical event for this time of year is the latest sunrise. The date is variable, depending on latitude. In Key West, Florida, the latest sunrise occurs on about January 14. In Denver, Colorado, it is about January 5, and in Anchorage, Alaska, the sunrise turns around after December 26. As the sunrise moves earlier, our Northern Hemisphere days lengthen more noticeably. If you want to find the exact date for your location, you can use the US Naval Observatory website, . You can also get a table of the duration of daylight from this site. Data is available for the whole world, so you can see how days are shortening now in the Southern Hemisphere as well.