Whats Up, Ron? is a monthly almanac for Northern American astronomersastras


by Ronald A. Leeseberg, the Star Geezer

September 2011 - Vol. 15 No. 9

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Features: Calendar | Lunar Almanac | Monthly Topic

This Month's Night Sky - NOTE: The next paragraph describes the sky as it appears at 10 pm EST (11 pm EDT) near mid- month. The sky also looks this way at 11 pm EST (midnight EDT) during the beginning of the month and at 9 pm EST (10 pm EDT) by month's end.

Angular Measurement Review: It is interesting to note that the relationship between the angle subtended by combinations of fingers on your fully outstretched arm are the same for all viewers. This is due to the fact that the hand's size is proportional to the arm's length. A shorter arm is attached to a smaller hand while a longer arm is attached to a larger hand, thus the angle measured remains the same. If you hold your arm fully outstretched, your little finger, when sighted down your arm, is one degree wide. Your three middle fingers is five degrees, your fist, 10 degrees, and the distance between your little finger and your pointer finger is 15 degrees no matter what your age or size.

Although fall begins this month, the Summer Triangle still glows nicely almost overhead. If you fortunate enough to have a dark observing site, follow the stars of the Milky Way (the visible "arm" of our galaxy) E to the famous "W" asterism of Cassiopeia. Arcturus (Bootes) now slips below the NW horizon and Capella (Auriga) shines in the NE. Another famous asterism, the Great Square of Pegasus, shines high in the SE, far above lonely Fomalhaut (Piscis Austrinus), glowing on the horizon. In the E find Aldebaran (Taurus) and the other stars of autumn. In the N, Ursa Major's asterism, the Big Dipper, "rides' low in the night sky.

MERCURY reaches it peak altitude in the early morning sky early this month. By the 8th , it will appear some 10 degrees above the E horizon about a half hour before sunrise. It disappears from view during the third week of the month. VENUS makes a very short appearance about a half hour after sunset at monthís end. Since it shines so brightly, sharp eyes might see it against the glare of the setting Sun. MARS rises in the ENE at around 2 AM. It is still too far away to see surface details. Bright JUPITER rises around 10 PM at the beginning of the month. By monthís end, it will be visible during the end of twilight. Its best telescopic view occurs at around 11 PM through midnight. SATURN glows low on the W after twilight at the beginning of the month. It sinks ever lower in the night sky until in disappears from view at midmonth. The SUN arrives at the equinox on the 23rd of this month. This marks the beginning of fall in this hemisphere and of spring in the Southern hemisphere.

Calendar of Events

NOTE: For those observers not in the ET zone, convert the calendar times to your zone's time by subtracting one hour for CT, two for MT and three for PT. Don't forget to adjust for Daylight Savings Time when necessary by subtracting one hour from your planisphere's time.; Dawn and dusk times must also be corrected. See your local newspaper, TV news, or cable TV's Weather Channel for sunrise and sunset times. Unfortunately some of these events may occur during daylight hours in your area.

The Moon occults (covers) the bright star, Delta Scorpii (Scorpius) for observers in the SE US. For most of us it will be a close pseudo-conjunction
Look E about a half hour before sunrise to see a very close pseudo-conjunction (less than a degree) of Mercury and the bright star Regulus (Leo)
See a conjunction of Jupiter and the gibbous Moon as they rise together after sunset.
See a conjunction of Mars and a fat crescent Moon just before sunrise.
The Autumnal equinox occurs at 5:05 AM EDT as fall begins.
The Zodiacal Light or "false dawn" is visible in the E about 2 hours before sunrise. This pyramidal glow is caused by meteoroids, dust particles spawned by passing comets, etc., that have settled into the ecliptic plane (path followed by the Sun, Moon and planets), reflecting the Sunís light before it rises here. This phenomenon will be visible until about October 10th as long as the Moon does not interfere.
The very thin crescent Moon appears just a few degrees above the E horizon at about a half hour before sunrise. You may need your binoculars to view.
At dusk, look very low in the W to see a close conjunction (2 degrees) of Saturn and Venus. Note the thin crescent Moon about 10 degrees to their left.
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Lunar Almanac for September 2011

Phases of the Moon Phase and Date(s)

Best viewed before local midnight


Deep Space Objects

1st. Qtr

Planets & Moon



Qtr 20

Deep Space & Planets

Topic of the month: Astronomical Filters

Filters are used to enhance oneís view of an astronomical object. They work by blocking part of the visible spectrum and passing the rest.

Of course, there are different filters for different objects. Below are the basic filters used for solar system objects.

filters for telescopes

Colored filters are specified by their Wratten numbers. This standard was developed by Kodak in 1909 and has been used ever since for astronomy, photography, stage lighting, etc.

The moon filter is used to view a full, "fat" crescent or a "fat" gibbous Moon. It is an example of a "neutral density" filter, to reduce brightness without affecting color very much.

The #80A light blue filter is used to study the upper atmospheres features of Jupiter and Saturn. It reduced red, green and yellow wavelengths.

The #58 green filter is used to increase the contrast of Martian ice caps, clouds and dust storms. It is also used to study red and blue features of Jupiter, and low contrast features of Venus and the Moon. It can also be used to enhance "white light" solar flare in conjunction with an appropriate objective-covering solar filter. It reduces red and blue wavelengths.

The #25 red filter is used to observe Marís ice caps and other surface features. It is also used to observe the bluish clouds of Jupiter and Saturn. It reduces blue wavelengths.

The #15 yellow filter is used mainly to view features on the Moon. It improves the contrast between features of different brightness as well as penetrating the atmospheres of Mars, Saturn and Jupiter. It reduces blue wavelengths.

Of course there are many other colored eyepiece filters but the above makes a good basic set.

I generally use only the four that I keep in a rotary filter holder.  The holder fits all of my telescopes (some ‘scopes need adapters.).

rotary holder for telecope filtes image

As you can see from the image above that position one is open, containing no filter at all. Frankly this is the one I use most often! The SkyGlo filter is used at night to reduce the effect of light pollution. The Moon filter is used to reduce eye fatigue when observing the Moon in its brighter phases.

The Green and Hydrogen Alpha filters are used when observing the Sun in conjunction with a full objective solar filter. The green filter increases the contrast between the surface of the Sunís Photosphere (surface) and white light flares.

The hydrogen alpha filter blocks most of the Sunís light except the tiny amount radiated by the Chromosphere (ďatmosphereĒ). Although not "narrow band" enough to block all of the light, it does allow the viewing of loops and prominences present on the Sunís ďedgesĒ.

(Iíve been known to flip the green filter into the optical path to "prove" that the Moon is made of green cheese.)

--See you next month!
Ron, the star geezer

This installment of "Whats Up?" is ©2011 Ronald A. Leeseberg, encoded by Dawn Jenkins for Astra's Stargate. Images used in this installment of "Whats Up?, Ron"are ©2011 by Ronald A. Leeseberg.

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