Exploring The Earth: Hudson's Bay And The Last Ice Age

(EXPLORING THE EARTH will be a regular series of columns that will examine various aspects of Earth Science through the lens of The Layered Earth software.  This first feature in this series examines the affect of the last ice age on Hudson Bay and how The Layered Earth software can be used to illustrate several unique features of this geological event.)

Hudson Bay, in north-eastern Canada, is one of the most prominent physical features of North America.  Today it is the second largest bay in the world, after the Bay of Bengal, east of India. 

The physical location of Hudson Bay in North America.

Sixteen thousand years ago, however, Hudson Bay lay crushed beneath an ice sheet that was 3 km (1.9 miles) thick. 

The extent of the ice sheet covering North America 16,000 years ago.

Layered Earth Software Users: To view the ice sheet covering much of North America 16,000 years ago:

  • Click on the Layers button in the bottom left corner of the screen.
  • Navigate through the following subdirectories:
  • CLIMATE → ICE COVER (insert a checkmark inside this box by clicking with your mouse inside the box)→ MAPS
  • Click the radio button for 16,000 YEARS AGO.
  • (Note: Clicking other radio buttons in this section will allow you to explore how the extent of the ice sheet has varied over time. Go ahead and explore!)
  • Click the Reset button in the tool bar (upper part of screen) in order to return to the default Earth view when you have finished exploring in this section.

This ice sheet was so heavy that it actually depressed the Earth’s crust underneath it.  Hudson Bay only finally became free of ice sometime between 8,000 – 9,000 years ago.  The removal of this immense ice burden allowed the depressed crust under Hudson Bay to slowly rebound.  This rebounding continues to this day.  Evidence of a depressed crust under Hudson Bay can still be seen today in gravity anomaly maps of the area.  The entire Hudson Bay area still exhibits a negative gravity anomaly; this means that the measured value of g, the acceleration due to gravity, is less than it should be as a result of the depressed crust.

The negative gravity anomaly in the Hudson Bay area.

Layered Earth Software Users: To view the gravity anomaly data set:

  • Click on the Layers button in the bottom left corner of the screen.
  • Navigate through the following subdirectories:
  • GEOPHYSICS → GRAVITATIONAL ANOMALY (insert a checkmark inside this box)→ MAPS

The gravity anomaly data will now appear on the globe, however, a clear view of the data is obstructed by the underlying satellite view of North America. To enhance your view of the gravity anomaly data:

  • Go to the SATELLITE IMAGERY subdirectory. Click on the checkmark in the box beside the subdirectory name. This removes the checkmark in this subdirectory and removes the satellite imagery data as active data.
  • Go to TOPOGRAPHY AND BATHYMETRY → COASTLINE AND BORDERS (insert a checkmark inside this box)
  • Click the radio button for N. Amer. States and Provinces. You should now have a clear view of the gravity anomaly data along with state/provincial outlines in North America in order to give a clearer geographical context.
  • (Small points representing stars are still visible in the background at this point. If you want to remove these then remove the checkmark in the box beside the ATMOSPHERE AND STARS subdirectory.)
  • Click the Reset button in the tool bar (upper part of screen) in order to return to the default Earth view when you have finished exploring in this section.

Clear physical evidence of the rebounding of the Earth’s crust (known as isostatic rebound) can be found by carefully examining the shore of Hudson Bay.  Once such area can be located at 56.390N, 87.950W.  You can rotate the globe manually until you locate these coordinates, or you could use the Search function

This unusual view of the Hudson Bay coastline can be found at 56.390N, 87.950W.

You should now be able to see an unusual series on lines on the land surface that are parallel to the coast.  What you are looking at is a series of old beach levels that mark the location of previous shorelines on Hudson Bay.  They are now inland because of the isostatic rebound of the crust under Hudson Bay.

Explore up and down the coast of Hudson Bay to discover other areas that nicely illustrate these previous shoreline levels.  Another particularly nice example of old shorelines can be found at 58.430N, 93.100W. 

Reference Files

Ready access to all of the views and data sets that have been mentioned in this article are available if you own The Layered Earth Software.  Each file (after it has been downloaded) can be viewed by clicking File/Open in the upper menu bar, and then following the path to its location.

Venus Kisses Saturn On Friday Jan. 8

On Friday, January 8, the planet Venus will appear to pass just 5 arc minutes north of the planet Saturn, That is a mere one-sixth of the diameter of the moon, a small enough distance to fit in the eyepiece of a powerful telescope.

On January 9, the planet Venus will appear to pass just north of the planet Saturn. Credit: Starry Night software.

This will be a rare opportunity to see two planets at the same time in a telescope’s narrow field of view. In a lifetime of observing the skies, I have seen such a close conjunction of two planets only two or three times. With the naked eye, sharp-eyed observers will be hard pressed to separate the two points of light.

Unfortunately for observers in North America, the point of closest conjunction will occur at 11 p.m. EST, while the planets are below the local horizon. For a skywatcher in New York, for example, the planets won’t clear the eastern horizon until 5 a.m. EST, at which time they will have separated so that they are 17 arc minutes apart, or slightly more than half the diameter of the moon. Even so, they will still fit in a telescope eyepiece.

Of course, this conjunction is something of an optical illusion. The two planets aren’t anywhere near each other in space, but merely appear close together from our perspective here on planet Earth.

Venus is currently on the far side of the Sun from Earth, 1.22 astronomical units distant (1.22 times the average distance from the Earth to the sun), so it appears similar to a gibbous moon.
Saturn is 10.79 astronomical units from Earth, nearly 9 times farther away than Saturn.

The two appear almost the same angular diameter: 14 arc seconds for Venus, 15 arc seconds for Saturn, yet in reality Saturn is actually almost 10 times the diameter of Venus. So Saturn’s greater distance balances out is larger size, and the two appear almost the same from Earth.

The most striking difference between the two is their difference in brightness. Venus is magnitude –4.0 on the upside-down brightness scale astronomers use, while Saturn is only magnitude +0.5, 4.5 magnitudes (or almost 100 times) fainter than Venus. This difference is mainly due to Venus’ closeness to the sun (0.72 astronomical units) compared to Saturn’s (9.55 astronomical units).

When you look for the twin planets just before dawn on Saturday morning, the first thing you will notice is Venus shining brightly in the southeastern sky. You will have to look closely to spot “tiny” Saturn just above and to the right of it.

If you own a planetarium program like Starry Night that lets you travel to other planets, check out the view Saturday morning from Saturn. You will see Earth and Venus in a close conjunction, Venus a narrow crescent from Saturn’s perspective, and Earth a rounded gibbous shape, since despite being close in the sky, they are actually on opposite sides of the sun, and lit by it quite differently.

Never stop improving! Starry Night 7.4.1 update is now live!

More than a year and a half into the release of Starry Night 7 we are still working furiously to bring fresh improvements and features to Starry Night. Developers see software the same way that artists see their creations - always in need of improvement.

 

7.4.1 Release Notes

New Features:

- Added a preference to support drawing selection labels as plain text (as in V6), instead of textured tags.
- Added Drag-Drop support for dropping SNFs onto the Starry Night sky to open.
- (Enthusiast) Added "Night Vision" mode.
- Added back Ambient Audio.
- Exported Observing Lists now include J2000 positions.
- Remembers your last open/save folder locations and defaults to these on File > Open/Save.


Fixed Bugs / Improvements:

- Fixed setting panoramas in locations that have pre-defined associations (e.g. Toronto, Detroit.)
- All log entries now show up in search results (was missing some with parentheses in their name.)
- Fixed Custom horizon images and editing.
- Fixed date formatting display (OSX).
- Fixed Meteor Shower radiant drawing. (Was too dim on OSX).
- Fixed movie creation of very large movies (OSX).
- Fixed trackpad click and drags (OSX).
- Fixed Constellation search results.
- Planet elongation correctly reported. (Was always showing zero.)
- Equipment List saved immediately on dialog close. (No loss if crash.)
- Satellites no longer use advanced magnitude calculations when not valid (i.e. far above Earth.)

 

The best part of making software is knowing that the changes you make affect so many people who use your creation regularly. The improvements made to satisfy your need for perfection benefit many!

So fire up your Starry Night 7 and tell us what you think about the latest changes!

Falling Leaves And Autumn Skies

The autumn sky shows the transition from the summer Milky Way, through the “watery” constellations of autumn, to the bright stars of winter. Credit: Starry Night software.

Autumn is the favorite season for many skywatchers. You can get your last look at summer stars and, if you stay up late, your first look at winter stars. Best of all, it gets dark earlier and the night temperatures are still comfortable.

Our graphic this week shows a panorama of the sky looking south around 8 p.m., just after the sky becomes fully dark. After the change to standard time this weekend, this will be the view at around 7 p.m.

Looking towards the west, at the right in the graphic, you can see the familiar constellations of summer. Sagittarius and the core of the Milky Way Galaxy are setting in the southwest, while the summer triangle: Deneb, Vega, and Altair, shines overhead.

It’s not too late to revisit some of the popular summer objects: double stars Albireo and Epsilon Lyrae, the globular clusters in Hercules and Ophiuchus, the Ring Nebula in Lyra, and the bright nebulae and clusters of Sagittarius.

Looking south, the upside down triangle of Capricornus rides high. Its rightmost star, Algedi, is a naked-eye double. Above Capricornus, just to the left of Altair, is the tiny constellation Delphinus, the dolphin, one of the few constellations that actually looks like its name. It’s worth exploring the region between Altair and Albireo, where you will find two of the finest deep sky objects: Brocchi’s Cluster, popularly called “the coat hanger,” and the Dumbbell Nebula, one of the largest and brightest planetary nebulae.

Many of the constellations in the autumn sky have watery associations. These include Capricornus (the sea goat), Delphinus (the dolphin), Aquarius (the water bearer), Pisces (the fish, plural), Piscis Australis (the southern fish, singular), and Cetus (the whale). Most of these are lacking in bright stars, with the exception of Pisces Australis which contains the first magnitude star Fomalhaut, the first star to have one of its planets directly imaged by the Hubble Space Telescope.

Although Aquarius is dim in terms of stars, it contains a number of fine deep sky objects, including the globular cluster Messier 2, and two fine planetary nebulae, the small bright Saturn Nebula snd the huge Helix Nebula. The latter is probably the planetary nebula closest to the sun, about 700 light years distant, and as a result is very large in size, almost as large as the moon. Because of its large angular size, its light is spread out over a wide area, making it very hard to see. You will need a narrow band filter on your telescope to spot it. 

Off to the east, the Square of Pegasus dominates the sky. This consists of three stars in Pegasus with the fourth corner of the square being marked by Alpheratz, the brightest star in the constellation Andromeda, which trails away to the northeast.

Right in the upper left corner of the graphic are the two largest and brightest galaxies in our neighborhood, the Andromeda Galaxy and the Triangulum Galaxy. These are located symmetrically on either side of the second pair of stars eastward from Alpheratz in Andromeda.

The Andromeda Galaxy (to the north) is large and bright. If you live in a city, you will need binoculars to see it, but sharp-eyed observers in the country, including myself, have spotted it with their unaided eyes. The Triangulum Galaxy is almost as large, but nowhere near as bright as Andromeda. It is best seen in small binoculars. Oddly, it is very hard to see in the narrow field of a telescope because its dim light is spread across such a large area.

Finally, in the northeast you can see the first of the winter stars, the bright star Capella in Auriga and the brilliant Pleiades Cluster in Taurus. Soon Orion will arrive in the east, in the words of Robert Frost:

            You know Orion always comes up sideways.

            Throwing a leg up over our fence of mountains,

            And rising on his hands, he looks in on me…

 Stay up until midnight, and you will see him, too.

 

Spot The Bright Asteroid Vesta

The next two weeks are an excellent opportunity to spot the brightest of the asteroids, Vesta.

In the first six years of the 19th century, astronomers discovered four new members of the solar system. All four were small objects moving in orbits between the orbits of Mars and Jupiter. Initially they were called planets, but by mid century, enough new objects had been found in this area that they were given a category of their own, much as Pluto was reclassified from a planet to a dwarf planet. They were called asteroids because all were so small that they looked just like stars in the telescopes of the day. Now there are tens of thousands of known asteroids.

Vesta is the brightest of all the asteroids, ranging between magnitudes 5 and 8, and one of the largest, measuring 318 miles (512 km) across. It reached 6th magnitude at opposition on September 29, meaning that it could just barely be seen by someone with perfect eyesight at a perfectly dark site.

The rest of us have to make do with binoculars. Heres how to find it.

A wide angle view of the autumn constellations, showing the position of the asteroid Vesta in Cetus. Credit: Starry Night software.

The first chart shows its overall position among the constellations of autumn. The two left-hand stars of the Square of Pegasus, Alpheratz and Algenib, point southward across the circlet of Pisces to the constellation Cetus, the Whale. Look for a large triangle formed by Eta and Iota Ceti and Deneb Kaitos. The last is easy to spot because, although only second magnitude, it is by far the brightest star in this rather dim part of the sky. Eta and Iota are both magnitude 3.5, so quite a lot dimmer than Deneb Kaitos.

A close up of the westernmost stars of Cetus, showing the position of the asteroid Vesta over the next two weeks. Credit: Starry Night software.

The second chart shows these three stars in detail, and the path of Vesta over the next two weeks. The end of Vestas path with the label is its position on Wednesday, September 30, and the points on the trail to the right show its position each night after that.

Vesta should be quite easy to spot, since it is about two magnitudes brighter than any of the stars along its track. Just to be sure, make a simple plot of the stars in its vicinity, and then check again a night or two later. The star that has moved is certain to be Vesta.

Vesta is now one of the best known objects in the solar system because it had the NASA spacecraft Dawn orbiting it for over a year (July 2011September 2012). This is a great chance for you to see it with your own eyes.

The Super-Blood-Moon Lunar Eclipse

This Sunday evening, 9/27, stargazers will see a rare supermoon lunar eclipse. If you miss it, the next one isn't until 2033! What makes this event so special?

A Full Moon

First, the moon will be full, as it always must be for a lunar eclipse to occur. This is a special full moon, all on its own, because this is the harvest moon. Traditionally, this designation goes to the full moon closest to the autumnal equinox. In two years out of three, the harvest moon appears in September, but every third year it occurs in October.
 
At this time of year, corn, pumpkins, squash, beans, and wild rice—the chief Native American staples—are ready for gathering; and at the peak of the harvest, farmers could work into the night by the light of this full moon.
 
Most of the year, the moon rises an average of 50 minutes later each night, but for the few nights around the harvest moon, the moon seems to rise at nearly the same time each night: just 25 to 30 minutes later across the United States, and only 10 to 20 minutes later for much of Canada and Europe.

A Supermoon

Secondly, the full moon will be at its closest to Earth in all of 2015, what is known to astronomers as a perigee moon. In recent years this has become known as a “supermoon.” Perigee (meaning “closest to Earth”) occurs at 10 p.m. EDT, the moon being a mere 222,374 miles (357,877 km) from Earth.
 
In fact, the human eye can’t detect the 5 percent difference in size between the moon at perigee and the moon at apogee (farthest from Earth), but everyone who looks at the moon Sunday night will swear it looks bigger than usual. Partly that is because, when seen low on the horizon, the human eye and brain combine to create an optical illusion known as the moon illusion, whereby the moon (and other objects) seen close to the horizon seem larger than when seen overhead.
 
The moon is the same size regardless of how low or high it is above the horizon. To prove this to yourself, cut out a circle just big enough to block the moon at arm's length and use it to see for yourself that its size stays the same as it rises in the sky.
 
The only noticeable effect of a perigee moon is that the ocean tides will be a bit higher than usual for the day of full moon and the next three days.

A Total Lunar Eclipse

The third, and most important part of this special event, is that we will have a total eclipse of the moon. At most full moons, the sun, Earth and moon line up approximately, but because of the tilt of the moon’s orbit, the moon passes above or below the Earth’s shadow, and avoids being eclipsed.

At certain points in the moon’s orbit, sun, Earth, and moon line up exactly, and the Earth’s shadow falls across the face of the moon, and we have a lunar eclipse. This is what will happen Sunday night.

The moon’s shadow has two parts: a darker inner part called the umbra, and a lighter outer part called the penumbra. This is because the sun is not a point source of light, so its light leaks around the edge of the Earth, and results in an unsharp shadow. In passing through the Earth’s atmosphere, the light turns red or orange, so that the light that actually reaches the moon is tinted by thousands of sunsets and sunrises all around the periphery of the Earth.


One result of these multiple sunrises and sunsets is that the moon during an eclipse is often tinted red, which is the origin of the idea of a lunar eclipse being a “blood moon.” It isn’t a far stretch of the human imagination to turn this “blood moon” into a portent of disaster.

A lot has been made in the media of this eclipse being the fourth event in a foursome of total eclipses known as a “lunar tetrad.” There really is nothing unusual about four lunar eclipses in two years, since we usually average at least two lunar eclipses every year, though not all are total.
 
In fact, there was no tetrad of total eclipses at all, because the last lunar eclipse, on April 4, was not really a total eclipse. According to the usual way of calculating eclipses, the moon spent only 4 1/2 minutes in the umbral shadow, but recently this calculation method has been corrected, resulting in the April eclipse failing to be total at all.
 
This Sunday’s lunar eclipse is a true total eclipse, with the moon being in the umbra for a full hour and twenty-two minutes.

When To See It

Observers in eastern and central regions of North America will get to see the whole eclipse; those further west will see the moon rise already partially eclipsed. Observers in Europe and Africa will see the eclipse before dawn on Monday, September 28.
 
This brings up the question of dates and times, which often causes confusion. Even a usually reliable source like Canada’s Weather Network, got the date of this eclipse wrong.
 
Officially, mid-eclipse occurs on September 28 at 02:47 Universal Time, which is the same as Greenwich Mean Time (but NOT British Summer Time). Subtracting 4 hours, this places mid-eclipse in the Eastern Daylight Time zone at 10:47 p.m. on the evening of September 27; the date changes at midnight. So be sure you look for the eclipse on Sunday evening. If you wait until Monday evening, you will be a day late.

Here are the important times in Eastern Daylight Time; if you’re using CDT, MDT, or PDT, the times will be earlier by 1, 2, or 3 hours.
 
EDT
08:11:46  Moon enters penumbra
09:07:12  Moon enters outer edge of umbra
10:11:11  Moon completely in umbra
10:47:09  Mid-eclipse
11:23:07  Moon begins to emerge from umbra
12:27:06  Moon completely out of umbra
01:22:33  Moon leaves penumbra
 
As always, we look forward to your pictures of this beautiful event.