Video From Barrow, Alaska, the day of Sunrise

We’re well south of Barrow, but when the sun rises there we know the Earth is really tilting more toward the sun. A video was taken by the FAA last Sunday, and to quote from the Weather Service Facebook page:

“Residents of Barrow, Alaska watched the sun climb above the horizon for the first time in 65 days, after it set on November 18, 2012. The sun skirted along the southern horizon for about 43 minutes today. Tomorrow it will remain above the horizon for 1 hour and 27 minutes. The amount of sunlight will rapidly increase in Barrow until May 10th, at which point the sun will remain above the horizon for 24 hours a day for nearly 3 months.”

I can’t seem to get the video to show on the page, but click here and you can see the Barrow sunrise.

Sunrise (and Sunset) in Fairbanks, Alaska

I had to share this video. For years I worked in an office with a south window just a block down the street from the museum from which this was taken, and I have seen the low arc of the sun over the Alaska Range. This video was on the Alaska Dispatch as a time-lapse of the Mayan Apocalypse (which just happened to be the Winter Solstice) with comments from the photographers.

The museum (and my old office) are on a ridge north of the Tanana Valley, with the main part of Fairbanks to the southeast, and part of the residential portion of College directly to the south. The bright patch below the Alaska Range on the horizon is the sun reflecting off the top of the ice fog; the discrete streamers are exhaust from chimneys.

Day and Year Lengths of the Planets

I went to an Alaska Writers Guild meeting Tuesday night, and mentioned Friday’s post on the effect of orbital tilt. This led to a discussion of day length, and I realized that while I knew some planets had really weird day lengths, I wasn’t sure which ones. (I thought it was the inner planets, which turned out to be right.) So as long as I was looking the information up, I thought I’d share it.

Mercury

Mercury turns out to be the planet whose days are longer than its years. For many years the planet was thought to keep the same side facing the sun all the time: one rotation about its axis relative to the stars for each revolution around the sun. We now know it rotates three times for each two revolutions around the sun, making its days a year and a half long. Luckily it’s a short year (88 Earth days.) Its tilt, by the way, is so near zero it is hard to measure. (Its closeness to the sun doesn’t help.)

Venus

Venus is the really weird one. Its rotation is in the opposite direction from its revolution around the sun, so from the surface of Venus, the sun would appear to rise in the west! At perihelion the sun may actually appear to stand still or go backward in the sky. That is, it would if you could see the sun through the sulfuric acid clouds. A Venusian day is long, however: 116.75 Earth days. A Venusian year is 1.92 Venusian days or 224.65 Earth days long. The tilt of its axis is only about 3.4°.

Mars

Mars is easily the least different from Earth when it comes to day length: 24 hours 39 minutes and slightly more than 35 seconds. This is more precise than is generally stated for the other planets, quite simply because Mars is the planet with human-piloted rovers on its surface, and to have daylight, these pilots must work on Martian days (or sols) even though they are located on Earth. (Pilot may not be quite the right word, given that radio communications take 4 to 20 minutes to get to Mars.) Its axial tilt is also similar to Earth’s: 25.2°. A Mars year is 1.8809 Earth years.

Jupiter

Jupiter has the fastest rotation rate, and thus the shortest day, of any of the planets: slightly less than 10 hours. Why the vagueness? All we can see of Jupiter is the cloud tops, and those rotate at slightly different speeds at different latitudes. It is clear, however that Jupiter’s days are very short, especially compared with its year length of 11.86 Earth years. Its axial tilt is small, only 3.13°.

Saturn

Saturn, like Jupiter, rotates fast and the rotation seems to vary with latitude but is slightly more than 10 hours. The year, however, is over twice the length of Jupiter’s – 29.46 years. The axial tilt is relatively large: 26.73°, which is why the visibility of Saturn’s rings from Earth varies so much. Seasonality is probably weakened by internal heating and the large distance from the sun.

Uranus

Uranus rotates slower than the gas giants but still faster than earth, with a day length of 17 hours, 14 minutes. Its year is 84 Earth years long. It is a few years past an equinox (2007) and won’t reach another solstice until 2028. There is some question as to which is the north pole, since its axis is either tilted at 97.77° with normal rotation or 82.14° with retrograde rotation.

Neptune

Neptune has a day length of roughly 16.11 hours. Very roughly – Neptune has even more variation in rotation rate of the cloud tops with latitude than does Jupiter, with apparent rotation periods varying from 12 hours at the poles to 18 hours at the equator. Its tilt is a little larger than earth’s, about 28.32°, which should give it pronounced seasons, though not as pronounced as those of Uranus! It year is roughly 164.8 years.

All of this variation is just in our own solar system. What else may be out there?

If the Earth were on its Side …

Click the image to get the links to participating blogs.

What point at the top of the atmosphere gets the most solar radiation on the day of the summer solstice?  Would you believe the North Pole?

Yes, that’s right. If the Earth’s pole of axial rotation were perpendicular to its orbital plane, the North Pole wouldn’t get any incoming radiation, and summer solstice would not even be defined. But with an axial tilt of only 23.5°, the pole still gets more radiation over 24 hours on the date of the summer solstice than any other point of the northern hemisphere on any date. Only the South Pole gets more, on the day of the winter solstice.

It doesn’t show up in temperature, first because much of the incoming solar radiation is scattered away during its long path through the atmosphere, and second because the ice and snow at the North Pole reflect much of the radiation back to space. (The second factor may be changing, and this is one of the reasons the Arctic is such a sensitive region.)

But suppose the axial tilt were 90°?

Uranus, as viewed by Hubble.

We do have one planet in our Solar System that approaches this: Uranus, with a tilt of 82.14°. But let’s stick with the Earth and assume it has a tilt of 90°. What would the seasons be like?

Summer solstice at the pole would be unbearable. Imagine the sun directly overhead at noon. Now stretch that noon out in time, so that the sun stays overhead for 24 hours. Hot? No place on Earth has that much incoming solar radiation today. Granted there would probably be clouds. In fact, there would probably be hurricane-like monsoonal storms unknown on our planet today. But it would still be hot.

By contrast, the South Pole would be in the middle of a six-month long night. It would have some stored heat left from the intense summer, probably enough to keep maritime climates above freezing. But it would still be dark except for the stars, the moon, and the southern lights.

The equator? At summer solstice, the equator would be pretty chilly. The sun would never rise or set, but just appear to sit at the northern horizon. As time moves toward the autumnal equinox, the sun gradually begins to rise in the north-northeast at 6 am, ride to its maximum height in the northern sky, and then set in the north-northwest at 6 pm. By the equinox, the sun would rise in the east, rise to directly overhead and then set in the west. But at the north pole, the sun has been spiraling gradually down the sky from overhead, until it finally just glides along the horizon at both poles on the day of the equinox, which begins a 6-month night for the North Pole and a 6-month day at the South Pole.

What happens if you add up all of the incoming solar energy over the course of a year? Not too surprisingly, the poles are the winners, with the equatorial regions being relatively cool. Given that water is much better at storing heat than land, the oceans would be warmer at the poles than the equator. Land areas are far more likely to follow a strong annual cycle. High-latitude continental climates would have tremendous seasonal variation, while maritime climates would be much more uniform. Monsoons, which are driven by these land-sea differences, would be extreme. And equatorial climates, which on our earth are primarily wet or dry, would be intensely cold near the solstices and as warm as they get on the equinoxes.

I haven’t actually tried this as a science fiction world—I want my planets to be habitable! But I do have a planet with zero axial tilt—Eversummer—in Tourist Trap. To quote Marna, the planet’s name must have been picked out by a publicity agent!

Note that today is the midsummer blog hop, and you can enter the draw for prizes by commenting. The prize on this blog is a PDF of one of my books, Homecoming or Tourist Trap (your choice.) In addition, anyone who comments on this blog is eligible for the grand prize drawing: 1st Prize – winner’s choice of a Kindle Touch or a Nook Touch
2nd Prize – a library of science fiction romance titles donated by various authors and an Anabanana Gift Card. Most of the books will be in digital format, with one print anthology.

No more than one comment on a single blog will count, but you can comment on multiple blogs to improve your chances.

The Transit of Venus

The reflector I used to see Venus was the large tube at the far right. The tan circle with the orange tube just to its left is the one that produced the shadow image shown below.

Tuesday was the last opportunity I’ll ever have to see the transit of Venus with my own eyes, and Alaska is one of the places where it was (theoretically) visible from beginning to end. Local astronomers with properly shielded telescopes were set up by the Noel Wein Library in Fairbanks, so since the sun was actually shining around 2, I took off to see the fun.

I said theoretically because while the sun was up for the duration of the transit, and the transit was visible (unlike a solar eclipse) from anywhere that the sun was visible, it’s been cloudy most afternoons. I set out with more hope than expectation, as towering clouds were visible in all directions. (It had hailed the day before.)

Sunlight came and went.

I’m not going to repeat in detail the reason why transits of Venus are rare—the Wikipedia article I’ve linked to does a good job of that. Basically, the orbit of Venus is inclined to the orbit of Earth by 3.4°, which means that Venus appears actually to cross the sun only when both planets are very near the line of nodes, the line defined by the crossing of the two orbits, at the time Venus comes closest to Earth. Last Tuesday was the last time this century that this will occur.

Shadow image of the sum. Venus is the small dot at the lower right. (Click on any photo to enlarge.)

By the time I made it to the library, the lawn sprinkled with telescopes was sunlit – most of the time. Clouds were scudding back and forth over the sun, and a thunderhead was towering to the east and headed our way. (Yes, thunderstorms often move from east to west up here.) I got a look at the sun through a properly filtered reflector during a break in the clouds, and later managed a photograph of a setup where a small telescope was focused on a mirror that produced an image on a white card. Literally minutes later the sun was covered with dark clouds.

This was taken minutes after the shadow image. Note there are no shadows–the viewing was over for the moment.

I’m glad I had a chance to see this. I’m not a big observer of astronomical events, but I got to watch the total solar eclipse in 1963, any number of lunar eclipses, the partial eclipse last month (via a pinhole camera) and now the Venus transit of 2012. Wish I could find my solar eclipse photo – it was spectacular.

Skywatching: DVD Course Review

Every now and then I order a course on DVDs from The Great Courses. Most recently, I’ve been viewing Skywatching, a course by Alex Fippenkio on the sky, day and night: what can be seen in it and the physics of why it looks the way it does.

Roughly the first third of the course deals with what we can see in the daytime sky. Dr. Filippenko discusses sky color in midday and when the sun is rising or setting, clouds, lightning, and the interaction of sunlight with water and ice (giving rainbows and halos.) This is closely related to what I researched and taught, so I didn’t really lean anything new. The presentation, however, was generally good. I did catch an error in one diagram, but I suspect that was the graphic designer. (The diagram is the one used to explain polarization in reflected light, and the error is that the angle of reflection and the angle of incidence are not shown as equal.) I was also rather disappointed that Dr Filippenko did not point out that frozen droplets are initially near-spherical, and develop their hexagonal prism shape (and the optical effects this produces) only later, by vapor-phase growth. But I suppose I shouldn’t expect everyone to be familiar with ice fog.

This section of the course should be of particular interest to writers needing information on sky and cloud cover, storms, and less common phenomena such as rainbows or sundogs. If you are going to describe an evening sky, you’d better have some idea of what’s happening.

Roughly half the course deals with the constellations and observing the bodies of the solar system. Most of this I was familiar with as an amateur, and I’ve used some of it — lunar phases and seasons, for instance — in my writing. Every writer who wants to put a moon in the sky should watch the section on lunar phases. Rising crescent moon in the evening? Nope. Just doesn’t happen. Neither does a narrow crescent high in the sky.

The lecture on solar eclipses brought back the one I saw, shortly after I moved to Alaska in 1963. I didn’t have a car yet, but two other graduate students gave me a ride down to Sourdough, Alaska to see the total solar eclipse of July 20, 1963. There were scattered high clouds, and while they added suspense –would the sky be clear during totality? – they wound up adding to the experience. Every bright spot of Bailey’s Beads had its own rainbow (technically iridescence.) I know I took a picture; I remember taking photos both before and after the eclipse, the ones after being a series with the exposure set at a constant value to capture the change in the light. I found that series, but so far the ones before and during totality are missing. They may have been separate from the others and lost during the fire twelve years ago.

Overall I’d give the course an A. Dr. Filippenko is a wonderful teacher, and with few exceptions the graphics are excellent. The course takes 3 DVDs and consists of 12 45-minute lectures.

Index of Science Posts

Here are links to all of the posts I would count as science, including those that explain how I use science in my science fiction. This list will be updated as new science posts are added. (Note that some posts listed under “Health” or “Technology” may also be of interest.)

The Science Behind Homecoming 4/2/10
Why do we have Weather? 4/24/10
Precession – Astronomy and Milankovitch 5/6/15
The Four Horsemen of the Apocalypse 6/12/10
Why Planets Have Seasons 6/24/10
Full of Sound and Fury (Fireworks) 7/3/10
Tricycles are not Bicycles 8/8/10
Planet Building 8/15/10 – 10/24/10
Racemization 9/2/10
Equinoxes and Daylight Savings 9/23/10
Horse Color Genetics 10/31/10 – 5/8/11
R’il’nai, Humans and Crossbreds: Life Span 12/11/10
Conservation Laws of Energy and Teleportation 12/20/10
Winter Solstice 12/22/10
Mass into Energy 12/24/11
Momentum and Teleportation 1/1/11
Snowflakes 1/7/11
Ice Fog: Ground Level Contrails 1/25/11
The Planets of Tourist Trap: Eversummer 3/6/11
Earthquakes, Tsunamis and Volcanoes 3/13/11
Why 12-Hour Days Already? 3/19/11
Ice Sculpture: Ice and Sun 3/26/11
More on Ice Melting 3/27/11
Why Temperatures Remembered Don’t Match the Record 4/5/11
When It’s Springtime in Alaska 4/8/11
Twilight 4/12/11
How High the Moon? 4/15/11
Breakup 4/16/11
The Cambrian Explosion 4/22/11
How Did We Learn to Walk? 4/29/11
Back to the Water 5/6/11
Where did the First Plants Come from? 5/13/11
The Geophysical Institute 5/15/11
Alaskan Mosquitoes 5/19/11
Colored-Leaf Geraniums 5/20/11
Early History of the Geophysical Institute 5/22/11
The Fairbanks Flood of 1967 5/29/11
Before Computers 6/5/11
Ice Ages and Alaska 6/17/11
Cumulus Clouds and Cloud Streets 6/24/11
Plate Tectonics Part I 7/1/11
Plate Tectonics Part II 7/8/11
Plate Tectonics Part III 8/5/11
Frost Hollows 8/19/11
Be Careful What You Ask For 8/27/11
Autumn Colors 9/10/11
Thermometers in Fairbanks 9/17/11
Junk Mail and Plants 9/20/11
The Chimney Sweep 9/22/11
Lights, Batteries, Temperatures? 9/24/11
How Dry I Am 10/15/11
Keeping Windows Dry 10/22/11
Snowflakes 10/29/11
The Alaskan Mesozoic 11/1/11
Mesozoic Alaska Part 2 8/11/11
Alaskan Mesozoic 3 11/15/11
Death of Blue Babe 11/17/11
Nightlength Sensitivity in Houseplants 12/10/11
Our Sense of Smell 12/17/11
What Time of Day is Warmest? 12/31/11
Alaska Winter Weather: Cordova and Nome 1/14/12
Inversions and Smokestacks 1/28/12
January Wasn’t Warm in Alaska 2/4/12
Fog, Fog, Fog 2/11/12
Oceanography DVD Review 2/14/12
Snow Festoons 2/18/12
Disturbance Hardening of Snow 3/24/12
Cold-Packed Snow and White Ice 3/31/12
Tornadoes and Climate Change 4/7/12
Breakup Season 4/14/12
Ice Jam Floods 4/21/12
Calories and Weight 5/5/12
Battery Woes 5/12/12
IRT Plastic: Using the Sun 6/2/12
A Love Affair with Begonias 6/7/12
The Transit of Venus 6/9/12
How does Rain Form? 6/16/12
If Earth were on its Side 6/22/12
Day and Year Lengths of the Planets 6/23/12
Chickweed and Mosquitoes 6/28/12
Flowers and Sex 6/30/12
Salpiglossis (Painted Tongue) 7/5/12
How Long is your Night? 7/7/12
Colorado Storm 8/2/12
Could Jarn have Made Glass? 8/11/12
Seeing the Jet Stream 8/18/12
A Bird in the Hand 8/23/12
Radiation Frosts 9/1/12
Alaska Sky 9/25/12
Sky Photo 9/27/12
Flower Photos 10/9/12
Start of the Seasonal Snowpack 10/18/12
Sunrise and Sunset in Fairbanks (video) 12/27/12
Video from Barrow, Alaska the first day of Sunrise 1/24/13
We Have Puddles! 4/20/13
DNA: We All Have it 6/1/13
My Maternal DNA 6/8/13
Winter Solstice in Fairbanks 12/21/13
Glaciation 4/8/14
Mints, Part 1 6/2/14
Mints, Part 2 6/5/14
Rosemarys 6/12/14
Thymes 6/17/14
Basils 6/19/14
The Summer Solstice 6/21/14
Other Culinary Herbs 6/24/14
Lavenders 6/26/14
Annual flowers in Alaska 6/28/14
First Daylily of 2014 7/1/14

Why an Index?

With 550 posts as of today, I’ve started to have problems remembering what I’ve already put on here. This is particularly a problem with posting existing content such as poems, short pieces from the Summer Arts Festival, or science explanations originally written for the Alaska Science Forum. I can’t remember which books or DVDs I’ve posted reviews on. It also is starting to be a problem when I want to link to a previous post and can’t remember when it was put up or what the title was. And there are posts on this blog that have permanent information, like the series on planet building and the one on horse color genetics, or the book and DVD reviews. I want to make it easier for my readers as well as myself to find things.

I made a start some time ago by adding an index page, which can be accessed from the menu at the top of any page. Right now, the only links are to index pages on my author site. This takes you out of the site and sometimes back in, which is rather clumsy. The index list is also incomplete.

I’m going to start posting an occasional entry which is strictly an index of past posts on a particular topic. These posts will be linked from the index page, and will link forward to the individual blog posts. As it takes a while to find all the posts that belong together, this will be a slow process—probably extending over the next few months. The first in this series, on DVD reviews, is already queued for January 3. Others will follow, most on Thursdays.

I probably won’t be indexing every post. Some, like those early posts which were simply glossary entries for my books, are on the author site and really belong there. Others, like the regular Monday updates on North Pole weather starting in November 2010, can be found easily enough just by using the calendar on the site. But I hope that by the time I have finished this, older posts of interest will be easier to find.

How High the Moon?

The waxing moon is shining in my window at night, now, but it is lower on the horizon every day. I don’t mean it’s later when I go to bed; I mean that the moon follows a lower arc in the sky every night, even as it becomes fuller. What’s going on?

Waxing gibbous moon, looking south before sunset April 14.

I’ve done a good deal of talking about the sun being lower each day in the sky until the winter solstice. Since then the sun has been higher in the sky each day, though it’s still only 35 degrees above the horizon at noon, and will never go above 48.6 degrees here at 64 degrees 50 minutes north. But what about the moon?

The moon goes around the earth  approximately in the same plane the earth goes around the sun. (We’ll get to the “approximately” later.) That means that when the moon is full, it is opposite the sun in the sky. If the sun is way below the horizon at solar midnight, as it is around the winter solstice, the full moon will be high in the sky. In fact, it will follow nearly the same path on the winter solstice as the sun follows on the summer solstice. On the summer solstice, the full moon will barely peek above the southern horizon.

The new moon, on the other hand, is in nearly the same place in the sky as the sun. The new moon will follow approximately the same path as the sun. The new moon will be very low in the sky in winter, and very high in the summer.

What about other phases? Right now the moon is waxing gibbous — that is, it is between first quarter (when it looks like a half circle in the sky) and full. On April 14 its highest altitude was 26.5 degrees; tomorrow it will be 20.3 degrees. Effectively, it is following the same path as the sun did in mid-March. I won’t even try to go through the mathematics and geometry involved, but for practical purposes the waxing moon is highest in spring, with the first quarter being highest near the vernal equinox (northward equinox, on the Confederation calendar) and the third quarter being lowest. In fall, this is reversed, with the waning moon being higher in the sky.

Up until now, we’ve been assuming that the moon’s orbit is in the same plane as the Earth’s. If that were really true, we’d have two eclipses — one lunar and one solar –each month. In fact, the moon’s orbit is slightly inclined to the ecliptic — about 5 degrees, to be exact. The direction of the inclination changes due to the pull of the earth’s equatorial bulge, which causes the plane of the orbit to precess with a period of 18.6 years. The inclination of the orbit makes the moon appear to move slightly above the sun’s path in the sky for half a lunar cycle, and slightly below it for the other half. Which part of the cycle depends on time of year and where the moon is in its precession cycle, but it is possible for the moon to be circumpolar or to remain entirely below the horizon here in the Fairbanks area, even though we are south of the Arctic Circle.

Right now, eclipses are near the solstices, so we won’t see the full moon stay below the horizon all night in summer, or be above the horizon at solar noon in the winter — though I’ve seen it in other years.

Twilight

No, it’s not about the books. But yesterday I mentioned that we no longer have astronomical night, and I felt that some definitions were in order.

End of civil twilight, available light photo looking NNW at 10:10 pm last night.

Twilight is defined as the period between the first traces of scattered light in the sky and sunrise, and between sunset and total darkness (other than starlight and moonlight.) It is actually divided into three periods each in the morning and evening, with boundaries determined by how far the sun is below the horizon.

Civil twilight is the period between the sun being on the horizon (sunrise and sunset) and the sun being 6 degrees below the horizon. If the sky is clear and you have good vision, you can generally see well enough to drive without lights, though your car will certainly be more visible to others if you turn your headlights on. The brightest stars and planets become visible after sunset and fade out before sunrise during civil twilight, but it’s not a very good time for even casual astronomy, except for watching the new moon, Venus and Mercury. Local laws generally define the limit of civil twilight using the time (30 minutes before sunrise and after sunset, for instance) but that can be very far off at high latitudes. Here in Fairbanks, for instance, it never gets darker than civil twilight from May 27 to July 28.

Nautical twilight is the period when the sun is 6 degrees to 12 degrees below the horizon. It was originally defined as the time when it was possible for sailors to make star sights, as most of the stars were visible but so was the horizon at sea. Here in Fairbanks it never gets darker than nautical twilight from April 26 (two weeks from now!) to August 18.

Astronomical twilight is defined as the period when the sun is 12 degrees to 18 degrees below the horizon. Ideally, when the sun is more than 18 degrees below the horizon 6^th magnitude stars should be visible. Sadly, this is no longer true anywhere in the vicinity of city lights, and in most places the difference between astronomical twilight and civil twilight is imperceptible. Here in Fairbanks, it does not get darker than astronomical twilight from April 9 to September 4. City lights are not a great problem up here, but aside from a brief period in September good astronomical viewing coincides with temperatures far too low for comfortable star gazing.

Twilight is very short at the equator, where the sun sinks or rises vertically at a rate of 15 degrees an hour . This gives only 24 minutes for each stage of twilight. Sunsets and sunrises seem very abrupt. At higher latitudes the sun seems to slant down to (or up from) the horizon, and twilight (and sunrise and sunset colors) can last much longer. I’ve tried to incorporate this in Homecoming — the sunsets and sunrises are very short on Marna’s tropical island, for instance.