Locate Ursa Major, Ursa Minor, Bootes, Virgo, Saturn and Leo

Locate Ursa Major, Ursa Minor, Bootes, Virgo, Saturn and Leo

Postby rene-gedaly » Sat May 18, 2013 5:19 pm

This first entry will be designed for evening observers.

For all observing, you may use either a planisphere to orient you to the sky or print out a current evening map from http://www.skymaps.com. If you use a planisphere, use the outer index to line up the time of night (in standard time, you will have to use an hour earlier if it is daylight saving time) with the date. If possible, find a planisphere designed for our latitude of 30 degrees north. Otherwise the more easy to find 40 degrees north version will be close enough. If you use skymaps, their northern hemisphere map is exact for 40 degrees north or about the latitude for New York, so for us, constellations to the north will be somewhat lower in the sky and constellations to the south will be higher. You may also use the map in the May issue of Sky and Telescope magazine.

NAKED EYE CHALLENGE

Locate Ursa Major, Ursa Minor, Bootes, Virgo, Saturn and Leo.

The best way to learn constellations is to start out with one of the easiest to see and then use it to point to other constellations. We are going to start out with one of the most basic groups. Please bear with me if you are already past this stage. In the city, you will only see the broad outline of constellations at best and if it is hazy, you may only be able to see the very brightest stars. Being able to find and identify these stars will help you find the entire constellation in a dark sky. And if you have a go-to computer controlled telescope, you will at the very least need to be able to identify some bright stars to get started observing. For most constellations, I am going to give you a link to the H A Rey outlines from his book "Find the Constellations" which help to see each constellation as a cartoon. I have never forgotten these versions and still see them when I look at the sky.

To begin, face north and locate the Big Dipper which is well above the horizon.

Big Dipper area HARey lines.gif


The Big Dipper is an "asterism" or group of stars with an interesting shape, but not a true constellation. It is a piece of the Great Bear or Ursa Major as you can see on your map.

bigdipper_med_labeled.jpg


Stars are normally designated by Greek letter in order of brightness in a constellation, but the Big Dipper is a rare case where this is not true. Instead, the stars are lettered in order from the front top front of the pot to the tip of the handle.

It is a good idea to become familiar with at least the first 7 or 8 Greek letters. Brighter stars will be labeled by the lower case letters on a star atlas. I am including the Greek alphabet here.

greek.gif


See if you can identify the stars of the Big Dipper by Greek letter.

big_dipper_Greek letters.png


Once you locate the Big Dipper, use the pointer stars at the front of the pot to locate Polaris, the North Star (actually located about 3/4 of a degree from the north celestial pole, but close enough!). Go from the front bottom of the pot to the front top of the pot (don't be confused if the Big Dipper is upside down!) and then continue in that line about five more lengths of that distance until you run into the only star bright enough to see in the city (and it will still be faint). That is Polaris, the tip of the handle of the Little Dipper, and it should be about 30 degrees up from the north horizon in "altitude" (with overhead being 90 degrees) and due north in "azimuth." The only other stars visible in the city in the Little Dipper, which is part of Ursa Minor the Little Bear, are the front two stars of its pot. Familiarize yourself with the almost yin-yang layout of the Big Dipper and the Little Dipper.

Next, use the handle of the Big Dipper to "arc to Arcturus," (the brightest star in Bootes) and "speed on to Spica" (the brightest star in Virgo).

follow-the-arc.jpg


Nowadays, Saturn is located to the left of Spica and appears about equally bright. Here is a video made for May 2012 which shows how to find these objects and also shows Saturn in 2012, 2013 and 2014. Be sure to note the 2013 position for use now. There is also good information on the stars you will see.

http://video.wpbt2.org/video/2217571805/

Big Dipper, Little Dipper, Bootes, and Virgo

http://starwalk.files.wordpress.com/201 ... he-arc.jpg

For Leo the Lion, which is high overhead, I always think of Leo as lying on the savannah underneath the table that the Big Dipper is set on. Its backward question mark head and mane and triangle of stars making up the rear end and tail are unmistakable. Regulus is the brightest star in Leo and is the bottom star of the backwards question mark. The double star Gamma Leonis or Algieba (note that star names are generally Arabic) is the lower of the two stars (relative to the question mark shape) in the curve of the question mark.

Leo-Coma-UMa-1024x781.jpg



BINOCULAR CHALLENGE

Alcor and Mizar

Now that you know the Big Dipper, use your binoculars to look at the double stars Alcor and Mizar located at the bend of the Big Dipper's handle. These stars are part of a six star system which may be gravitationally bound. In binoculars and a low power telescope, you will just see the two main stars about 12 minutes of arc apart. (60 minutes is a degree). This is wide enough to separate in binoculars and even possibly naked eye.

There are two main types of double stars: "Optical" doubles are accidents of line of sight and are not related geographically. "Binaries" are physically related to each other and rotate around each other. If Jupiter were about 20 times larger, we would be part of a binary star system.

http://en.wikipedia.org/wiki/Mizar_and_Alcor

The Moon

Also, look at the Moon. You will want to compare your view in the binoculars with that in the telescope to see how your telescope's optics alter the image. Is it upside down, reversed or both? Also, note which end of the "terminator" or boundary between night and day is closer to the north star so you will know which poles are north and south in your telescope. Now that it is first quarter and waxing, note the rabbit shaped dark patches visible. The head of the rabbit is the Sea of Tranquility where Apollo 11 landed. (Kids always want to know this.) You can also point out the rabbit shape at public star parties.

TELESCOPE CHALLENGE

First, if you are new to telescopes, start out by aligning your finder. It is easiest to use a terrestrial object such as a treetop or street lamp to align. Find the object in the finder and if it is close, it will appear in your widest field eyepiece. (The more millimeters your eyepiece, the lower the power and generally wider the field.) Center in your eyepiece and then use the three set screws on your finder to place the object in the center of your finder. Repeat with a high power eyepiece if desired. Now when you use your finder, the object will be in your eyepiece. Use low power first when finding a new object and then center and add higher power if needed. You should check this every time you begin an observing session.

Alcor and Mizar again.

Use their spacing to get an idea of the field of view of your eyepiece. They are 12 arc minutes apart, so five times that distance, or 60 arc minutes would be one degree. The sky from horizon to opposite horizon is 180 degrees.

Saturn

Note the angle of the rings. This changes over time in a long cycle of opening and closing, spending about 13 years on one side of edge on and 15 years on the other. Right now, the rings are well open. Here is a great web page about Saturn, which was at "opposition" (opposite us from the Sun) on April 28th. In Houston, you may be able to see Titan a little ways from the planet, and in a dark sky you can see up to five moons.

http://www.universetoday.com/101290/the ... pposition/
Gamma Leonis: beautiful yellow double star in Leo:
http://frostydrew.org/publications.dc/s ... /pss-obsy/

Moon

Right now is a fabulous time to view the Moon. Each night, different craters are highlighted near the terminator. A neutral density or moon filter screwed onto the bottom of your eyepiece will help cut glare. At first quarter (May 18th) and one to two days after you can see the large wall plained Clavius of "2001: A Space Odyssey" fame near the south end. It is about 125 miles across and has several smaller craters within. The Moon is about 1/2 degree across or 30' or "arc minutes." You can use the Moon to get a rough idea of the field of view of your eyepieces. My widest field eyepiece 32 mm eyepiece shows 66' (or one degree, 6 minutes) in my 8 inch F7 telescope. One degree has 60 minutes, and one minute has 60 seconds.

http://www.johnstonsarchive.net/astro/moonmap.html
Clavius and Tycho photo: (mouse over to identify)
http://www.flickr.com/photos/latent0image/7885373952/
My favorite crater Eratosthenes appears in strong relief about two days
after first quarter. Check out this wonderful video tour of the Moon at about the same phase:
http://www.youtube.com/watch?v=c8dhNV3W7n0
There are plenty of moon maps, atlases and resources on line.

Enjoy and I look forward to hearing about how you did! I am learning even more right along with you. Let me know if anything is unclear or if you have questions.

Debbie Moran, Novice Chair
[email protected]
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