Natural Calendar May 2009

Natural Calendar - May 2009

The purpose of this feature is to give scout leaders, educators and naturalists an idea of some of the natural events coming up each month. We will try to cover a variety of natural events ranging from sky events to calling periods of amphibians, bird and mammal watching tips, prominent wildflowers and anything else that comes to mind. We will also note prominent constellations appearing over the eastern horizon at mid-evening each month for our area for those who would like to learn the constellations. If you have suggestions for other types of natural information you would like to see added to this calendar, let us know!

Note: You can click on the hyperlinks to learn more about some of the featured items. To return to the Calendar, hit the "back" button on your browser, NOT the "back" button on the web page. All charts are available in a "printer friendly" mode, with black stars on a white background. Left clicking on each chart will take you to a printable black and white image. Please note that images on these pages are meant to be displayed at 100%. If your browser zooms into a higher magnification than that, the images may lose quality.

Notes and Images From April 2009

The Whirlpool Galaxy, Messier 51, April 4th, 6 inch Refractor at f12 and ST2000XCM CCD Camera, Total Exposure Time 90 Minutes. Click on the image for a finder chart.

For many people, a list of the most visually appealing galaxies in the sky would probably include the Whirlpool Galaxy. Its image, along with several others in a book I pulled off a high school library shelf, first inspired me to build a telescope. The 51st object in the catalog of Charles Messier, it is one of the easiest galaxies to find. If you aim your binoculars at the star that marks the end of the handle of the "Big Dipper," your field of view will probably include it. M51 is just outside Ursa Major in the small constellation of Canes Venatici, the Hunting Dogs. We took this 90 minute exposure on April 4th.

Messier 51 is actually two interacting galaxies, NGC 5194 and NGC 5195. NGC 5194 is on the right in our image. You can tell something of the ages of the stars in the galaxies by their colors. Older populations of stars are golden yellow, while newly formed stars are bluish. It is thought that the gravitational interaction between the two galaxies resulted in many new star-forming areas in NGC 5194. Distance estimates for the pair range from less than 20 million light-years to over 30 million light-years.

Messier 51 was discovered on October 13th, 1773 by Charles Messier, while observing a comet. His friend Pierre Mechain discovered the companion galaxy NGC 5195 on March 21st, 1781. The spiral arms were first seen by Lord Rosse in 1845, using the 72 inch telescope at Birr Castle in Ireland.

On a dark night, you can sometimes spot the Whirlpool in binoculars as a faint misty patch of light. For a binocular finder chart and suggestions for spotting it in binoculars, click on the above image.

Sky Events for May 2009:

Evening Sky:

Saturn is high in the southern sky at dusk as the month begins. The rings are almost edge-on, tilted only about four degrees. Because of the diminished brightness of the ring system, you may be able to see fainter satellites of Saturn than you normally do with a given telescope.

At the beginning of the month, look for Mercury low in the west-northwest sky about 40 minutes after sunset. It will sink lower each night until it disappears into the evening twilight by mid-month.

Morning Sky:

Jupiter rises a little after 2:30am at the start of the month and is about 30 degrees up into the southeastern sky by dawn.

Look low above the eastern horizon before sunrise for Venus and Mars. Try about 40 minutes before sunrise. Mars will be below and to the left of Venus, about 5 degrees away. The view below shows the pair, along with Jupiter, on May 1st. See if you can spot the crescent phase of Venus with your binoculars.

May 1st, 5:15am, Looking East Before Sunrise

All times noted in the Sky Events are for Franklin, Tennessee and are Central Daylight Time. These times should be pretty close anywhere in the mid-state area.

Constellations: The views below show the sky looking east at 9:30pm CDT on May 15th. The first view shows the sky with the constellation outlined and names depicted. Star and planet names are in green. Constellation names are in blue. The second view shows the same scene without labels. New constellations this month in the eastern sky are Lyra, the Lyre, with it's bright star Vega, Serpens Caput, the head of the Serpent, and Libra, the Scales.

May 15th, 9:30pm, Looking East

On Learning the Constellations:

We advise learning a few constellations each month, and then following them through the seasons. Once you associate a particular constellation coming over the eastern horizon at a certain time of year, you may start thinking about it like an old friend, looking forward to its arrival each season. The stars in the evening scene above, for instance, will always be in the same place relative to the horizon at the same time and date each May. Of course, the planets do move slowly through the constellations, but with practice you will learn to identify them from their appearance. In particular, learn the brightest stars (Like Vega, Arcturus and Spica in the above scene looking east), for they will guide you to the fainter stars. Once you can locate the more prominent constellations, you can "branch out" to other constellations around them. It may take you a little while to get a sense of scale, to translate what you see on the computer screen or what you see on the page of a book to what you see in the sky. Look for patterns, like the stars that make up the constellation Hercules.

The earth's rotation causes the constellations to appear to move across the sky just as the sun and the moon appear to do. If you go outside earlier than the time shown on the charts, the constellations will be lower to the eastern horizon. If you observe later, they will have climbed higher.

As each season progresses, the earth's motion around the sun causes the constellations to appear a little farther towards the west each night for any given time of night. If you want to see where the constellations in the above figures will be on June 15th at 9:30pm CDT, you can stay up till 11:30pm CDT on May 15th and get a preview. The westward motion of the constellations is equivalent to two hours per month.

Recommended:

Sky Publishing has a beautiful and compact star atlas, the Sky & Telescope's Pocket Star Atlas. It is destined to become a classic, and is a joy to use at the telescope.

A good book to learn the constellations is Patterns in the Sky, by Hewitt-White. You may also want to check out at H. A. Rey's classic, The Stars, A New Way to See Them.

For skywatching tips, an inexpensive good guide is Secrets of Stargazing, by Becky Ramotowski.

A good general reference book on astronomy is the Peterson Field Guide, A Field Guide to the Stars and Planets, by Pasachoff. The book retails for around $14.00.

Starry Night has several software programs for learning the night sky. Visit the Starry Night web site at www.starrynight.com for details.

Amphibians:

Bird-Voiced Treefrog

By the end of May all of Tennessee's frogs and toads are either calling or have already reached their peak calling period and are being heard less. The treefrogs are the last of our frogs and toads to start calling. Cope's Gray Treefrog and Gray Treefrogs start giving isolated calls as early as March, and by the end of this month listen also for Bird-Voiced Treefrogs, Green Treefrogs and Barking Treefrogs. In May we also hear Fowler's Toads calling frequently, so listen for their "crying baby" call. Northern Cricket Frogs are hitting their stride as well. Listen for a sound like two stones being tapped together. We have heard eight or more species of frogs calling on some May evenings, so it's a great time to listen. Upland Chorus Frogs and Spring Peepers continue to call. Listen for their calls to increase in pitch and quicken with the rising temperatures.

Birds:

Try to get out with a pair of binoculars in the early morning in the first two weeks of May to take full advantage of the spring migration. The later nesting owls like Eastern Screech Owls are nesting right now. In late May and early June, the young screech owls can sometimes be heard giving their raspy "begging" calls. Easier to hear is a sound that the adult owls make around the young owls, a downward slurred whistle about a half second in duration. This call sounds more like a puppy whimpering than an owl, but you can sometimes follow the sound and come upon a whole group of young screech owls on a tree limb.

Recommended:

Bird Finding in Tennessee, Michael Lee Bierly. A classic guide to finding birds in Tennessee.

The Sibley Guide to Birds, David Allen Sibley

The Sibley Guide to Birds of Eastern North America, David Allen Sibley

An inexpensive guide for beginners is the Golden Guide for Birds.