Happy September Equinox: An Explanation

 

September EquinoxToday is the September Equinox. You’ve probably already heard it a few times today; people running around proclaiming with utmost exuberance how today is the first day of Fall. In the Northern Hemisphere, the announcement is the harbinger of shorter days and dropping temperatures. But what is really going on today?

When someone says today is the first day of Fall, what they really mean (whether they know it or not) is that today represents an equinox; specifically, the September Equinox.1 On Earth, an equinox is the point in its orbit around the Sun when both hemispheres are equally illuminated; our tilted Earth lines up to a point in which the Sun passes directly over the equator. This happens twice a year, on the March and September equinoctes (that’s the plural form of equinox, use this information smugly).

Contrary to popular belief, the day of the equinox does not represent the day where daylight and darkness are equal. You can thank geometry, the atmosphere, and the Sun’s angular diameter to cause that equality to happen at different times geographically. What today does mean though, is that the equinoctes are the only two days in which the Sun rises due-East and sets due-West, and which the Sun would pass directly overhead from an observer on the equator.

One other very important thing that you must know if you don’t learn anything else today: Way too many people believe that the equinoctes are the only day of the year that an egg can be balanced on its end. While it is true that on the equinox an egg can be balanced, it’s also true of every other day of the year; it makes no difference!

There are other times during the year (read: our orbit around the Sun) that we recognize Earth residing at a special place.  There’s Perihelion and Aphelion, and then the widely-celebrated solstices, but I’ll save those for another time.

Happy September Equinox!

  1. What about them being called the Spring  and Fall (or their Latin names, Vernal and Autumnal) equinoctes? Well, that wasn’t exactly fair to those in the Southern Hemisphere, whose seasons are opposite those in the Northern Hemisphere.

Happy March Equinox: An Explanation

March Equinox graphic

Solstice and equinox diagram, showing the March equinox

Image Credit: NASA

Today is the March Equinox. You’ve probably already heard it a few times today; people running around proclaiming with utmost exuberance how today is the first day of Spring. After the long winters that some of us endure, the arrival of Spring is welcome news. But what is really going on today? After all, where I live it still feels like the middle of Winter, but flowers were already blooming on a trip I took to California a couple of weeks ago1. If we based “The First Day of Spring” on climate patterns, regions across the globe would be recognizing a wide variety of days throughout the year.

When someone says today is the first day of Spring, what they really mean (whether they know it or not) is that today represents an equinox; specifically, the March Equinox.2 On Earth, an equinox is the point in its orbit around the Sun when both hemispheres are equally illuminated; our tilted Earth lines up to a point in which the Sun passes directly over the equator. This happens twice a year, on the March and September equinoctes (which I learned today is the proper plural form of the word equinox).

Contrary to popular belief, the day of the equinox does not represent the day where daylight and darkness are equal. You can thank geometry, the atmosphere, and the Sun’s angular diameter to cause that equality to happen at different times geographically. What today does mean though, is that the equinoctes are the only two days in which the Sun rises due-East and sets due-West, and which the Sun would pass directly overhead from an observer on the equator.

One other very important thing that you must know if you don’t learn anything else today. Way too many people believe that the equinoctes are the only day of the year that an egg can be balanced on its end. While its true that on the equinox an egg can be balanced, it’s also true of every other day of the year; it makes no difference!

There are other times during the year (read: our orbit around the Sun) that we recognize Earth residing at a special place.  There’s Perihelion (which we went over in January) and Aphelion, and then the widely-celebrated solstices; but I’ll save that for another time.

Happy March Equinox!


This article originally posted on March 20, 2012.

  1. In fact, while it may have still been Winter to the San Diegans giving me quizzical looks for swimming in the ocean without a wet suit, to an Alaskan like myself it felt like an unusually warm Summer’s day!
  2. What about them being called the Spring  and Fall (or their Latin names, Vernal and Autumnal) equinoctes? Well, that wasn’t exactly fair to those in the Southern Hemisphere, whose seasons are opposite those in the Northern Hemisphere.

CleanSpace One

Space — particularly, low Earth orbit — is becoming a messy place. Thousands of satellites (both operational and defunct), spent rockets, and tons of fragments resulting from collisions and erosion of the former, circle our planet. Upwards of 16,000 of these objects larger than 10 centimeters are tracked by the United States Space Surveillance System1. While space, including low Earth orbit, is a vast place, collisions can, and have, happened.
Computer-generated image of tracked orbital debris.

[Click for larger version]
(Image Credit: NASA Orbital Debris Program Office)

In 2009, the US Iridium 33 communications satellite was destroyed when the retired Russian Cosmos 2251 collided with it. Not only did this collision have an effect, albeit minor, on global communications, it resulted in one of the greatest debris generation events to occur in low Earth orbit.2 It’s a compounding problem; debris and defunct satellites collide, creating even more debris.

Fixing Half Of The Problem
There are essentially two problems that we, as a spacefaring civilization, need to address: disposing of existing debris and preventing future debris in the first place. The Swiss Federal Institute of Technology (École polytechnique fédérale de Lausanne (EPFL)), has set its sights set on solving the latter, with their revolutionary satellite, CleanSpace One. The EPFL announced on Wednesday that it planned to develop and launch what is being nicknamed a “janitor satellite” as a trial demonstration of how satellites can be captured from orbit and be re-directed towards Earth’s atmosphere for a fiery disposal. The $10.8-million (USD)3 project will create a single-use satellite, which is expected to capture and de-orbit one of two currently-orbiting Swiss satellites, SwissCube and its cousin Tlsat-1.
Infographic summarizing how CleanSpace One will work.

(Image Credit: EPFL)

Yes, single-use. If you think $10-million+ is a lot of money to experimentally de-orbit a single satellite, I cannot help but to agree with you. However, if you look at CleanSpace One as the first step towards the long-term future of maintaining space, then you start to think that this is an important and worthwhile investment. Due to the increasing problem that space junk is becoming, the costs involved with creating and launching the spacecraft we put into orbit, and the insurance costs to protect that investment once you get it there, I strongly believe that cleaning up space is going to be a lucrative and necessary industry in the not-too-distant future.

Kudos to the EPFL for making this a priority. I hope one day we can look back on CleanSpace One and point to it as being an important first step in keeping the space around our planet tidy!

For more information on CleanSpace One, check out the following video. The satellite capture method is particularly intriguing.


  1. The Air Force Space Surveillance System, which is colloquially known as the “Space Fence”, detects and catalogs objects as small as a baseball, between low Earth orbit all the way to an altitude of 30,000 kilometers (about 18,000 miles).
  2. Second only to the intentional destruction of Fengyun-1C, as part of a Chinese anti-satellite missile test. It created more than an estimated 35,000 pieces of new debris larger than 1 centimeter.
  3. 10-million Swiss francs.