Archive for the ‘Astronomy’ Category

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Happy Solstice!

Tuesday, June 21st, 2011

The June Solstice occurs at 17:16 UTC on 21 June 2011. On this date, the Sun reaches the northernmost line of latitude (the Tropic of Cancer, 23.5°N) where the midday Sun is at the zenith (the imaginary point directly overhead). At northern mid-latitude locations, the midday Sun reaches its maximum altitude (annually) and the duration of insolation (number of hours of daylight) is greatest. For example, in Washington, D.C. the midday Sun will reach an altitude of 74.5 degrees above the horizon and there will be nearly 15 hours of daylight (14h54m). Also, the Sun rises farthest to the north of east (to the far left of the Washington Monument in the accompanying photograph) and sets farthest to the north of west than at any other time of year.

It’s interesting to note that the apparent paths of the Sun and Moon across the sky are exactly opposite at the solstices: near the time of the June Solstice, the Full Moon follows the path of the Sun during the December Solstice; near the time of the December Solstice, the Full Moon follows the path of the Sun during the June Solstice. For more information, see Yin and Yang – Dynamic Equilibrium in the Universe.

Posted from Arlington, Virginia, United States.

Posted in Astronomy, Education, Nature | Comments Off

My NEW favorite times of day

Tuesday, May 17th, 2011

Two times a day, digital clocks display my new favorite times of day: 8:14 AM; and 8:14 PM. Digital clocks that show hours, minutes, and seconds — such as the Apple iPhone Clock Pro Free app (shown below) — display my favorite times as 8:14:54 AM and 8:14:54 PM. Are you curious about the significance of these times? 08/14/1954 is my birthday!

I still like my old favorite times of day, but since the word “favorite” is defined as “preferred before all others of the same kind” (Credit: Apple Dictionary widget), 12:34:56 AM/PM have been reclassified as “times of day I really like.”

Before noon in Washington, D.C.

After noon in Washington, D.C.

Are You Clock Wise? Did you know that “a.m.” and “p.m.” mean “ante meridiem” and “post meridiem,” respectively? In other words, before- and after the Sun crosses your meridian (line of longitude). Note that the time of day is neither a.m. nor p.m. when the Sun is directly over either your meridian or anti-meridian. (Refer to graphics captions, shown above, for proper nomenclature.) Ever wonder, “Why is ‘Clockwise’ clockwise?” In the Northern Hemisphere, shadows cast by the Sun move in a clockwise direction; as a result, the hands of analog clocks (see clock faces, shown above) are made to move in the same direction. In fact, the word “hour” means “the day” or “Sun’s path.”

Posted from Arlington, Virginia, United States.

Posted in Apple, Astronomy, Education, Sundials | Comments Off

Breaking news: TPE on sale this weekend only

Friday, April 15th, 2011

The Photographer’s Ephemeris app (TPE for iOS) — one of two noteworthy Apple iOS apps for planning photo shoots of the Sun and Moon — is on sale for $3.99 this weekend only. That’s right, for two days only you can buy TPE for less than the price of LightTrac ($4.99), a similar yet much less robust app. Don’t sleep on this extraordinary offer!

Posted from Arlington, Virginia, United States.

Posted in Apple, Astronomy, Digital Photography, Product Reviews | Comments Off

The Not So Big Moon

Monday, March 21st, 2011

There was a lot of excitement about the so-called “Super Full Moon” on Saturday, 19 March 2011. Lots of people photographed the event. I wonder how many of those folks looked at their photos and thought, “That’s not what I saw!” The fact of the matter is the camera doesn’t lie. The apparent diameter of the Moon (and Sun) is less than 0.5 degrees, or about 1/50 the width of most photos. Prove it to yourself: The apparent width of your thumb held at arm’s length is about one (1) degree; you can easily cover the disk of the Full Moon with your thumb! Photos of the Sun and Moon are disappointing unless you use a camera with a telephoto lens.

So why does the Moon seem to appear so big when you see it in the sky? There’s no consensus among experts, but I think it’s due to frame of reference: The Moon looks much bigger when you see it near the horizon and are able to compare its size to objects like buildings, trees, etc. In contrast, the Moon looks much smaller when it’s high in the sky.

And while we’re talking about photographing the Moon, it’s a good time to mention two noteworthy Apple iOS apps for planning photo shoots of the Sun and Moon: LightTrac ($4.99); and The Photographers Ephemeris ($8.99). In my opinion, you get what you pay for: The Photographer’s Ephemeris (TPE) is more robust than LightTrac. TPE for Desktop, a FREE equivalent of the TPE app, works on all computer operating systems including Apple OS X, Microsoft Windows, and Linux.

Posted from Arlington, Virginia, United States.

Posted in Apple, Astronomy, Digital Photography, Education, Product Reviews, Windows | Comments Off

Triangle Solver

Saturday, March 19th, 2011

Remember “SOH-CAH-TOA,” the mnemonic for solving triangles? Forget it! Now there’s an app for that: Triangle Solver for Apple iOS devices. If you know two angles and one side of a triangle, then you can calculate the other values for the triangle. Triangle Solver also works when you know two sides and one angle, or three sides and no angles. Let’s look at a practical example.

How can you determine the height of objects too tall to measure directly, e.g., buildings, flagpoles, utility poles, trees, etc.? Using shadows, of course! Imagine the height of a flagpole is represented by side a, side c is the length of the flagpole’s shadow, and angle A is the angle formed between the ground and a line of sight from the top of the flagpole’s shadow to the top of the flagpole itself. As shown in No. 2 (below), I entered 51 degrees as the value for angle A and 90 degrees as the value for angle B (since we assume the flagpole is plumb with the ground). Notice that Triangle Solver automatically entered a value of 39 degrees (shown in red), since we know the sum of the interior angles of a triangle equals 180 degrees. If the length of the flagpole’s shadow is 10 meters (as shown in No. 3, below), then we see that the height of the flagpole is 12.349 meters (No. 4, below). Note that the sides of the triangle are units independent, meaning you can use any units you prefer.

Triangle Solver is simple to use, works as advertised, and it’s free!

Related Resources:

Teacher Tips: It is impractical to determine a line of sight to the Sun (one ray of angle A in the preceding example) without looking at the Sun itself. NEVER look at the Sun directly — blindness may result! A safer approach is to determine the apparent altitude of the Sun for a specific date and time. Altitude is defined as the height above the surface of a planet, measured as an angle between 0 degrees at the horizon and 90 degrees at the zenith.

Posted from Arlington, Virginia, United States.

Posted in Apple, Astronomy, Education, How To, Product Reviews | Comments Off

Daylight Saving Time begins

Sunday, March 13th, 2011

Remember the mnemonic: Spring forward; fall back? On the second Sunday in March (13 March 2011 at 2 a.m.), Daylight Saving Time begins and clocks are set forward one hour. Notice how much later sunrise & sunset occur! A sure sign that spring is springing: The number of daylight hours is increasing. By the time of the June Solstice (21 June 2010, 17:16 UTC), there will be ~15 hours of daylight in Washington, D.C. (14h54m) — the most hours of daylight all year!

Posted from Arlington, Virginia, United States.

Posted in Astronomy, Education | Comments Off

Groundhog Day

Wednesday, February 2nd, 2011

According to legend, if the groundhog sees his shadow on February 2nd then there will be six more weeks of winter; if he doesn’t see his shadow then there will be an early spring. Reality check: The fact of the matter is there will be six more weeks of winter regardless of what the groundhog sees!

For places located in the Northern Hemisphere, the first day of astronomical spring occurs on the March Equinox, when the subsolar point crosses the Earth’s equator. The March Equinox occurs on 20 March 2011 at 23:21 UTC. Do the math: There are six- to seven more weeks of winter between Groundhog Day and the March Equinox. Truth be told, numbers don’t lie.

Here’s a cold fact to warm your heart: On January 24th, the daily average high temperature in Washington, D.C. begins increasing from its lowest point annually. Yippee — winter’s icy grip may be slipping!

Teacher Tips: Visit Groundhog Day, the official website of the Punxsutawney Groundhog Club. Follow the hyperlink to “Teachers” for pointers to related activities and lesson plans.

Editor’s Note: Punxsutawney Phil did not see his shadow, and that means there will be an early spring. Let’s hope Phil’s prediction is right! This year, Groundhog Day is also Chinese New Year’s Eve. 2011 is the year of the rabbit. Happy New Year!


Posted from Arlington, Virginia, United States.

Posted in Astronomy, Education, Weather | Comments Off

Daylight Saving Time Ends

Saturday, November 6th, 2010

Remember the mnemonic: Spring forward; fall back? On the first Sunday in November (07 November 2010 at 2 a.m.), Daylight Saving Time ends and clocks are set back one hour to return to Standard Time. Notice how much earlier sunset occurs! A sure sign that winter is coming: The number of daylight hours is decreasing. By the time of the December Solstice (21 December 2010), there will be only nine hours and 27 minutes (9h27m) of daylight in Washington, D.C. — the fewest hours of daylight all year!

Posted from Arlington, Virginia, United States.

Posted in Astronomy, Education | Comments Off

Virtual Tour of the Solar System, Revisited

Saturday, July 31st, 2010

Take an interactive virtual tour of the Solar System beginning with the Sun, represented by the Sandburg Planetarium: Mercury; Venus; Earth; Mars; Jupiter; the asteroids (dwarf planets); Saturn; Neptune; Uranus; and Pluto (a dwarf planet). Both size and distance are shown using the same scale.

Fairfax County Scale Model of the Solar System

Tech Tips: Click on the red magnifying glass (shown left, map sidebar) to see a full-screen view of the map (optional, but recommended). “Zoom In” on the map in order to see the terrestrial planets.

The virtual tour is based in Fairfax County, Virginia (USA), but could be modified for use with other locations. See developer notes that explain how I created the tour. See also, Making a Scale Model of the Solar System, a classroom-ready activity for students. (Teacher’s Answer Key available upon request.)

Going Further: Download and install Google Earth. Download the virtual tour KMZ file: Double-click on the KMZ file icon; Google Earth launches automatically. Click the “Play Tour” button, located in the “Places” panel in the left sidebar.

Editor’s Note: This is the 50th post since I began blogging with WordPress. The original version of this blog post was published on 17 October 2009 under the title, Fairfax County Scale Model of the Solar System. I decided to update the original blog post by using the “XML Google Maps” WordPress plugin to add an embedded  interactive map of the virtual tour. While the embedded map adds visual appeal to the blog post, Google Earth is a better tool than Google Maps for viewing the virtual tour.


Posted from Arlington, Virginia, United States.

Posted in Astronomy, Education | Comments Off

My Favorite Times of Day

Sunday, July 11th, 2010

Two times a day, digital clocks — such as the Apple iPhone “Clock” app (shown below) — display my favorite times of day: 12:34 AM; and 12:34 PM. Digital clocks that show hours, minutes, and seconds display my favorite times as 12:34:56 AM and 12:34:56 PM.

After 12:00 midnight in Washington, D.C.

After 12:00 noon in Washington, D.C.

Are You Clock Wise? Did you know that “a.m.” and “p.m.” mean “ante meridiem” and “post meridiem,” respectively? In other words, before- and after the Sun crosses your meridian (line of longitude). Note that the time of day is neither a.m. nor p.m. when the Sun is directly over either your meridian or anti-meridian. (Refer to graphics captions, shown above, for proper nomenclature.) Ever wonder, “Why is ‘Clockwise’ clockwise?” In the Northern Hemisphere, shadows cast by the Sun move in a clockwise direction; as a result, the hands of analog clocks (see clock faces, shown above) are made to move in the same direction. In fact, the word “hour” means “the day” or “Sun’s path.”

Posted from Arlington, Virginia, United States.

Posted in Apple, Astronomy, Education, Sundials | Comments Off

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