Today Is the Winter Solstice – Here's What That Means

What’s A Solstice?

For many of us, December 21, 2016, marks this year’s Winter Solstice. But for plenty of others, it’s also the Summer Solstice. How can this be? What is actually unique about today from an astronomical sense? What is a solstice anyhow?

First, let’s be considerate of all people regardless of whether they live in the northern or southern hemisphere. Let’s refer to today’s event as the December solstice. We do this because while those of us that live in the northern hemisphere consider it to be Winter, our friends south of the equator are in the middle of their Summer. This, of course, is because the Earth is tilted on its axis–which means that for part of the year, the northern part of our planet is tilted towards the Sun (and thus receiving more exposure to solar radiation i.e. Summer), while the southern half is tilted away (less solar radiation i.e. Winter). The other half of the year, this is reversed. (If you live directly on the equator, you can call it whatever you want because you get to have Summer 365 days a year.)

A solstice occurs on the day when the planet’s hemisphere has its maximum (or minimum) amount of solar exposure (in December, it’s the northern; in June it’s the southern’s turn), which in turn gives us the longest and shortest days of the year. Contrast that to the equinoctes (yes, that really is the plural form of equinox), in which the length of day is equal to the length of night.

Now, you might have heard the solstices being referred to as the “First Day of Spring/Winter”, which if you live in a geographic area that has noticeable seasons you know this isn’t true. It would be more appropriate to consider a solstice as the middle of a season. Starting today, the daylight hours get longer in the northern hemisphere and shorter in the southern.

So where did the “First Day of Spring/Winter” idea come from?


I really don’t know.

If you find out, please let me know.

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.

2012 Transit of Venus

2004 Venus Transit

2004 transit of Venus through a small telescope. Click image for source.

Next Tuesday, June 5th (June 5th in North America / June 6 eastern continents), you’ll have the opportunity to observe something that you’re extremely unlikely to ever see again. Over the course of a few hours, Venus will cross in front of the Sun from the vantage point of Earth. Venus will appear as a small black dot against the bright blazing disc of the Sun. Just like the annular eclipse from a couple of weeks ago, it is NOT SAFE to view this event directly. Here are a few ways to view it:

Disposable solar shade glasses – This is the cheapest and simplest method. These are the same glasses you would use to view a solar eclipse. They’re generally made of cardboard and have extremely dark film for lenses. When looking through them, you cannot see anything except for something as bright as the Sun. If you can see the surrounding landscape through them, they are NOT dark enough and you are at great risk of damaging your eyes.

Pinhole projection – If you’ve got clear skies and an overhead Sun, you can project the image of the Sun (and transit) using a simple pinhole projector. This can be as simple as a piece of paper with a hole poked in it, to a more elaborate and larger projector. Feel free to be creative, as long as you do it safely. Here are some sources for pinhole project ideas: Cosmos Magazine / / Exploratorium

Binocular/Telescope projection – You can also project a magnified view of the transit by using a pair of binoculars or a small telescope. Here, you want to point the objective lens (the big lens away from the eyepiece) at the Sun, let the light go through the binoculars/telescope and project that image onto a shaded piece of paper. Experiment with different distances until you get everything in focus. Note, that doing this method for a significant amount of time can damage the optics in your binoculars or telescope.

Webcast – If the clouds have you down or the transit occurs during your night time where you live, you can still watch the event unfold from what will certainly be a number of online webcasts. My friends at Cosmoquest will be hosting a Google+ Hangout with various feeds of the transit, and Slooh will make an event out of it as well.

So now that you know how to look, you need to know when and where.

Map showing where the 2012 Venus transit will be visible from.[Map showing where the 2012 Venus transit will be visible from. Source: NASA / Click for larger view.]

Being an amateur astronomer in Alaska (especially along the coast) is the true definition of optimism. There are a lot of clouds year-round, never-ending sunlight during the Summer, and frigidly cold winters that make skygazing a test of tolerance and wills. That said, on those few nights where the clouds have retreated, it’s dark, and above zero… those nights are a-maz-ing. Coincidentally, Alaska is a prime viewing location for the 2012 transit of Venus — in fact, the entire event will be viewable from up here. Ironically, I’ll be out of the state during the transit and will only be able to catch it during a North Dakotan sunset (which sounds pretty, anyhow).

For the most accurate information for your location, there are a handful of resources. There are free iPhone and Android apps for your smartphone. Additionally, if you can find your location on a map this webpage is a fantastic guide. An example of how it varies from place to place:

My home in Kenai, Alaska (June 5th):
Venus crosses into the limb of the Sun at 2:06pm local time. Approximately 20 minutes later, Venus is fully within the disc of the Sun. It will slowly make its way across the face of the Sun over the next 6 hours, reaching the opposite limb at around 8:30pm local time. At 8:48, the show is over with the Sun still high in the sky.

Where I’ll be in North Dakota (June 5th):
The transit will begin at 5:04pm local time. By 8:27pm local time, Venus will be at the center-point of its transit. Around an hour later, the Sun will set, taking the transiting Venus with it.

The bottom line is, due to the duration of the event you should be able to get at least a glimpse of it from anywhere in North America, to a varying degree as shown above. And you’ll definitely want to make every opportunity to see it, because it will quite likely be the last time you have the chance — unless, of course, you plan on being alive for another 105 years (and still have the eyesight to see it!). That’s right, this will not occur again until 2117 — so this is your chance.

Good luck and happy observing!

Upcoming Solar Eclipse

Readers located in the Western United States and East Asia should mark their calendars for this Sunday’s (May 20, 2012) solar eclipse. To some degree, the eclipse should be observable from Texas to Thailand, with certain locales observing an annular eclipse, while others will still get the treat of a partial eclipse.

Track of the May 20, 2012 solar eclipse overlaid on a map.

(Image courtesy of Google and NASA’s Eclipse Web Site)

 Note, you do not need to be on that path in the picture above to see the eclipse. If you’re within that path, you will see an annular eclipse. If you’re North of South of that path, you’ll see a partial eclipse. An annular eclipse is a solar eclipse in which the distance between the Earth and the Moon is great enough that it appears too small to completely block out the Sun. It will look like this:

Eclipse Anular

Photo of a 2005 annular eclipse, as seen from Spain. Photographed by Abel Pardo López and used under a Creative Commons license. Click image for source.

Unlike the case with a total eclipse, where the Moon is closer to Earth and covers the entire Sun (less its corona), do not look directly at an annular eclipse with your naked eyes!

For those of us that will be outside the path of the annular eclipse, many will still be able to see a partial eclipse. Without going too deep into the geometry of an eclipse, be aware that there are basically three types of shadows produced during the event: the umbra, antumbra,  and penumbra. The umbra is the darkest part of the Moon’s shadow, and when it falls upon the Earth it results in a total eclipse. From within the umbra, the Sun is completely blocked out by the Moon. From the vantage point of an observer within the penumbra, the Sun is only partially blocked by the Moon, resulting in a partial eclipse.  Within the antumbra, an observer will see the Moon pass completely between them and the Sun, however its apparent size compared to the Sun will be small enough that it will not completely block out the Sun; an annular eclipse.

The following diagram is a visual demonstration of what I’ve just described:

Diagram showing the different types of solar eclipses.

(Image Credit: University of Tennessee Department of Physics and Astronomy)

“Okay, but I just want to know if I can see it!”

Okay, so you want to know if you’ll be able to see the eclipse, and if so, when should you look? The best and simplest way to find out is to go to NASA’s Eclipse Web Site for this event. From there, you can click on your location on the map and a little window will pop up with details, like so:

Details of the May 20, 2012 solar eclipse for Kenai, Alaska

If you live near Kenai, Alaska (like me) there are your details. Take note that the times are in Coordinated Universal Time (UTC), so you’ll want to adjust accordingly based on your time zone. In my local case the eclipse will begin at around 3:15pm local time (UTC – 9 [AK Time] + 1 [Daylight Savings Time]) and continue for nearly three hours, as the Moon slowly moves across the face of the Sun. For other locations, you’ll find this tool very easy to use.

“What good is knowing when and where an annular eclipse is if I’m not allowed to look at it?!”

I’m glad you asked! By all means, do NOT look at this eclipse with your naked eyes. You will damage them. The visual part of the electromagnetic spectrum is far too beautiful to go damaging your instruments to see it (your eyes!). Fortunately, there are a few simple tools you can use to view it.

The most convenient method is to use cheap cardboard solar-shield glasses made specifically for this purpose. You can buy them online and elsewhere for less than a dollar. (Buy many and share! They’ll also be great for the Venus transit next month, but more on that later!) They look like this:

Solar shield glasses

If you choose to purchase some (there may not be enough time to receive them before Sunday, but there will be plenty of future opportunities to use them as well), I recommend purchasing through a company associated with Astronomers Without Borders, where proceeds will go to benefit others interested in astronomy. Make sure any you use are clearly labeled that they’re safe to view the Sun through.  An alternative to these glasses is to use Number 14 Welders’ Glass, available at welding supply shops.

You can also use a pair of binoculars or a telescope as follows, but make sure that nobody (small children, non-bright adults, pets) looks at the Sun through the eyepieces; it could very well be the last thing they see. To use binoculars or a telescope, you want to project the image onto a piece of shaded white paper. Just align the Sun with the objective lens (not the eyepiece lens) and let the light pass through and onto the piece of paper. An image of the Sun will appear on the paper and, while bright, will be safe to look at.

And finally, if you do not have solar shield glasses, Number 14 Welders’ Glass, binoculars, or a telescope (again, projected onto paper!), you still have another option. You can use a colander, a piece of aluminium foil with a hole punched in it, or even with the aid of a leafy tree. Obviously, if you took a colander outside on a sunny day, let the sunlight shine through it, and reflect onto the ground, you would see the circular dots of light where it was allowed to pass through the holes in the colander, and shade where the solid part of the colander blocked it. If you happen to do this when the Sun doesn’t appear as a solid circular light source (an eclipse), or if something is passing in front of it (a transit), the light in those dots on the ground will show it as well.

Check it out!:

Partial eclipse viewed with the aid of a colander.

(Image Source)

This same effect will work if you poke some holes in aluminium foil, a pizza box, or whatever you might have available. Luckily, you’ll have a bit of time during the eclipse to experiment and see what works best.

Even trees want you to see the eclipse:

The Eclipse Tree, Basildon.

(Image Credit: Picture Esk on Flickr)

So that about covers it. If you have any questions, if I’ve missed anything, or if you believe there is a mistake in my explanations, please leave a comment. I hope you’ll take the opportunity to enjoy this celestial treat and I hope you find people to share the experience with you as well.

Happy observing!

Titanic Star Field Corrected for 100th Anniversary Release

Neil deGrasse TysonI first read this story on April 1st and thought it might possibly be an April Fool’s prank. It turns out it wasn’t.

Director James Cameron is re-releasing his 1997 film Titanic, to commemorate the 100th anniversary of that “unsinkable” ship’s sinking. He intends to change very little from the 1997 release but there is one change being made that makes reporting it fit the theme of this blog: when watching the movie at the theatre during its original release, astrophysicist Neil deGrasse Tyson noticed that the star field in the background of one of the scenes wasn’t accurate. But, instead of just filing that inaccuracy on the shelf with all of the other thousands of scientific errors you’ll find in popular movies and moving on, Neil deGrasse Tyson couldn’t let it go, and on more than one occasion allegedly attempted to alert Mr. Cameron of the error.

Here’s a 2009 video of Tyson describing noticing the mistake in Titanic and his attempts to make Cameron aware of the error (reload page if video doesn’t appear):

Apparently, James Cameron finally got Tyson’s message and told Tyson that if he got him the correct star field, he would include it in the anniversial re-release; Cameron told the UK magazine Culture:

Oh, there is one shot that I fixed. It’s because Neil deGrasse Tyson, who is one of the U.S.’ leading astronomers, sent me quite a snarky email saying that, at that time of year, in that position in the Atlantic in 1912, when Rose is lying on the piece of driftwood and staring up at the stars, that is not the star field she would have seen, and with my reputation as a perfectionist, I should have known that and I should have put the right star field in.

So I said, ‘All right, you son of a b****, send me the right stars for the exact time, 4:20 a.m. on April 15, 1912, and I’ll put it in the movie.’ So that’s the one shot that has been changed.

Neil deGrasse Tyson responded to a question posed by Alan Boyle of the Cosmic Log, who asked him if he Cameron might put his name in the credits:

“If he does, that’s fine,” Tyson told me. “I’m a servant of the public interest and the public’s appetite for information about the universe. I get these calls all the time. … The mere fact that an artist cares about getting the science right, and thereby transmitting that science literacy to the consumers of that art — that’s enough reward for me.”

ATREX – Observing the Air Up There

I suspect we might hear about strange sky phenomena and UFOs occurring over the US Eastern Seaboard tomorrow, thanks to NASA’s ATREX mission.
After previously being scrubbed, the next launch attempt has been set for the wee hours (2am – 5am EST, or what I might consider late tonight) of March 27. ATREX, or the Anomalous Transport Rocket Experiment, is designed to study ultra-high altitude, high-speed wind patterns that have been observed on the very edge of space1. Data suggests that 200 – 300 mile-per-hour winds occur at an altitude of 62 – 68 miles; though little is yet understood about the phenomena. The atmosphere at that height is incredibly thin, and it essentially takes a rocket to get there.

The project will complete its test with the use of five of what are referred to as sounding rockets, launched within minutes of each other. These sounding rockets are smaller than those that are used to achieve orbit or carry heavier payloads, but will work just fine for this experiment. After reaching an altitude of 50 miles, the rockets will release a chemical tracer that will be observed from camera facilities both North (New Jersey) and South (North Carolina) of the Wollops Flight Facility in Virginia. The chemical, trimethylaluminium, was selected due to its reaction to oxygen; it glows and produces aluminium dioxide, carbon dioxide, and water vapor (each already present in our atmosphere).

Diagram of ATREX mission
(Graphic showing various aspects of the ATREX mission. Click for larger version.)
[Credit: NASA/Goddard Space Flight Center]

If you’re not on the US East Coast, but still want to try and watch the show, NASA has a webcast available here: and a UStream will carry it here:

For more information, you can follow the Wollops Flight Facility on Twitter, and check out the video below.

  1. For an important point of clarification, when I use the term “edge of space”, I mean it literally. You will often hear about an amateur balloon going to space, or a sky-dive from or near space, but those are exaggerations in my opinion. In my book, we’re talking at least 50 miles (the point at which NASA gives you astronaut wings) or better yet, the Kármán line.

Sunday Matinee – Science In My Kitchen

While I recognize that this video is a departure from my primary focus on the space sciences, I just had to share this video. My kids and I made this video as we explored the interactions between milk and dish soap, using food coloring to make the interaction visible.

Kind of neat, yeah? The video should show you everything you need to know to try it yourself. The degreasing elements of the dish soap break up the fat in the milk (whole milk will work better than reduced fat), and the food coloring is along for the ride.

I bet you have everything you need to try this yourself, so what are you waiting for?

NASA Facebook Game – Space Race Blastoff

Image Credit: NASA

NASA recently released its first multiplayer Facebook game, Space Race Blastoff. It’s a competitive trivia game, in which you’re pitted against random opponents from around the world. You earn points for correct answers and bonus points for getting the correct answer first. I’ve played a few rounds and was actually surprised at how challenging some of the questions were. For example, you might be shown a photograph an astronaut and have to answer whom it is. I got Tom Stafford right, but didn’t recognize Stanley G. Love. Other questions aren’t specifically NASA-related, ranging from questions about the periodic table of elements to pop-culture references. If you’ve got a few minutes to spare and want a quick and fun test of your space sciences knowledge, give it a shot!

GRAIL: Ebb and Flow

Artist's Rendition of Grail Mission

Image credit: NASA/JPL-Caltech

Earlier this month, I gave a minor overview of NASA’s Gravity Recovery And Interior Laboratory (GRAIL) mission. I had mentioned that the two mirror-twin spacecraft that make up the mission were currently — and temporarily — dubbed GRAIL-A and GRAIL-B, with official names coming later in the month. Beginning last October, NASA appealed to elementary students to come up with replacement names for the spacecraft.

Over 11,000 students, from 45 states and several territories, participated in contest, making for stiff competition.

Ultimately, it was the 4th Grade students from Emily Dickinson Elementary school, in Bozeman, Montana, who were chosen as the nationwide winners of the naming competition, with their names of Ebb and Flow. The students arrived at their name by researching what the GRAIL mission was studying and how it worked. They learned how important the Moon is to our lives on Earth, and how the Moon’s gravity causes our high and low tides. They decided on Ebb and Flow, because the names represent both the Moon’s gravity and its effects on our home.

Congratulations Emily Dickinson 4th-Graders! Not only did you come up with great contest-winning names, you came up with names that will forever exist in the historical pages of the world’s exploration of space!

For more about GRAIL, check out these links:

Neil deGrasse Tyson on The Daily Show

Astrophysicist, and renowned promoter of science, Neil deGrasse Tyson, sat down for an interview on The Daily Show with John Stewart. As always, Neil’s commentary drips of a passion for discovery and exploration. Science and comedy mix well!