Most accurate from mid-northern latitudes of approximately 36-40 degrees, north;
(e.g. San Francisco, U.S.A. ** Madrid, Spain ** Tokyo, Japan)
Copyright (c) 1995 Pete Harris; **Back to Star Facts Home Page**
Updated for the month of: October, 1995
Do The Daily Differences in Length of
Day Seem Greater These Days ?If it seems like the day to day differences in the length of days is greater now than at some other times of the year, it's not your imagination. It is greater at this time of year. The day to day changes in length of day are greatest at the time of the Spring and Autumn equinoxes and are least in mid-summer and mid-winter.
Watch the Demon Star Get DimmerThe star Algol, meaning "Demon Star", belongs to one category of variable stars called "eclipsing variables". (See Star Facts article for October, 1995 The Mysterious Demon Star Dims...Then Brightens for fuller explanation). Variable stars change their brightness over a period of time. Algol gets dimmer approximately once every 2 days and 20 hours. It stays near its dimmest for about 2 hours, with the entire fading and brightening process lasting about 7 hours.
Algol is best seen beginning in autumn and into early winter. It is found in the northern constellation Perseus. See diagram below for graphical representation of Algol's position relative to Cassiopeia. The easiest way to find it is to face north and locate the constellation Cassiopeia, which looks like a giant and slightly squashed letter "M" in the northern sky. During early autumn evening hours the "M" is positioned sideways rather than right -side-up and Algol is not really high enough to see until about 11:00 p.m.. Extend the imaginary line from the "M" 's bottom center point to its top right point about 1 1/2 fist widths further (width of closed fist with arm extended) to a region to the upper right of the "M". In this region find a fairly bright star (not quite as bright as the stars that form the "M") in the center of a group of stars with no clear shape, this group is the constellation Persues. Algol is found a little less than 1 fist width above this central star (or above and right of, depending on time of night). Algol, in its bright state is about the same brightness as the central star.
Some of the times during October, 1995, when Algol reaches its dimmest point during North American night-time hours are Oct. 9 at 1:05 a.m. PDT (Pacific Daylight Time), Oct. 12 at 9:45 p.m. EDT (Eastern Daylight Time), and Oct. 29 at 2:46 a.m. PDT. Some other international times are Oct. 17 at 22:31 UT (Universal Time - Greenwich, England), Oct. 20 at 19:20 UT, and Oct. 23 at 16:09 UT.
To see Algol's changes in brightness use binoculars to look at it and some of the surrounding stars of similar brightness, one or two nights before the dates of its dimmest points. Make a sketch on a piece of paper with some notes about how it compares with one or two other stars. Then look again around the time of one of its dimmest points. See how the observations compare. At its dimmest, Algol should be about half the brightness that it is most of the time.
Three Planets in a Row !On the evening of October 18, 1995, 30 minutes after sunset, if you have an unobstructed view of the western horizon and you look quick, you can see the three planets Venus, Mars, and Jupiter all in a row, low in the western sky. On that evening Venus is just high enough from the Sun so that it becomes visible at dusk just before setting; Mars is a little higher and to Venus's left; and a still bright Jupiter is higher and to the left of Mars. The three planets are on a diagonal line that goes up and to the left of the horizon at about a 30 degree angle.
If you look too soon the twighlight will still be too bright to see anything. If you look too late, Venus will have set and Mars may be too close to the horizon to see. But if you look just right . . . you'll see three planets in a row!
Total Eclipse of the Sun, to be Seen
in AsiaA solar eclipse is probably nature's most awesome sight. On October 24, 1995, there will be a total eclipse of the Sun, visible in a line across the Earth that passes over southern and south-eastern Asia. This total solar eclipse will be visible from parts of Iran, Afghanistan, Pakistan, India, Bangladesh, Burma, Thailand, Cambodia, Vietnam and the southwestern Pacific.
A solar eclipse occurs when the moon passes directly in front of the sun from the vantage point of an observer on Earth and blocks out the Sun's light. During the few moments of total coverage the sky turns almost as dark as night, and stars are seen - even though it may be middle of the day !. When the observer looks out toward the horizon where some of the Sun's rays are still getting through, there is partial light, like at sunset. But strangely, the "sunset" is all around. The observer is surrounded by partially lit horizon in all directions.
The moon's diameter is about 400 times smaller than the Sun's diameter. Why then does the moon almost perfectly cover up the Sun during a total eclipse? Because, by coincidince the Sun is about 400 times further away. Therefore the two appear almost the same size from Earth. A word of caution: even during most of a total eclipse, it is extremely dangerous to look at the sun without special solar filters.
See pamphlet titled "Eclipses" from the Royal Greenwich Observatory in England for additional information about eclipses.
Andromeda, "The Great
Galaxy"Andromeda, shown as M31 on star charts, and known as the "Great Galaxy", is a galaxy 2.2 million light years away from the Milky Way, made up of hundreds of billions of stars. It is the furthest object in the universe that can be seen with the unaided eye, although that is only possible from very dark, clear locations. It is quite visible with binoculars or a low power eyepiece on a telescope. (See Star Facts article for September, 1995, The Andromeda Galaxy - the Most Distant Thing Human Eyes Can See" for further description).
Andromeda is best seen beginning in late summer and throughout the autumn. It is found in the constellation that bears its name - Andromeda. The easiest way to find it is to face north and locate the constellation Cassiopeia, which looks like a giant and slightly squashed letter "M" in the sky. During early autumn evening hours the "M" is positioned sideways rather than right -side-up. Using the left half of the "M" as an imaginary arrowhead, go about 1 1/2 fist widths (the width of your clenched fist held up to the sky at arm’s length) in the direction the arrowhead points in. Scan this area with binoculars to find the fuzzy patch of light that is Andromeda. Sweep back and forth over the area until you begin seeing its dim outer regions that give it an oval shape. (See beautiful time-exposure Photo of Andromeda from Jason Ware's home page).
The "Great Square"
Dominates Autumn SkyFour moderately bright stars, called the "Great Square" dominate the evening sky during autumn. The Great Square is easily recognizable because it is surrounded by what appears to be mostly empty sky. During early autumn evening hours it is found a bit east of directly overhead, passing overhead at about midnight (daylight savings time), and moving west as the night goes on. During late autumn evening hours it is virtually overhead as darkness falls, and moves west as the night goes on.
There are several interesting facts about the Great Square:
- It is actually a rectangle, not a square; but the "Great Rectangle" just doesn't have the same ring to it.
- The Great Square is not actually considered a constellation. It is part of the larger constellation Pegasus (the "Winged Horse" - good luck trying to see a horse). The Great Square is considered an "asterism" - a recognizable pattern in the sky that is part of one or more constellations. (Another example of an asterism is the Big Dipper, which is part of the larger constellation Ursa Major - the Big Bear).
- One of the four stars of the Great Square, the northeast corner, is actually not in Pegasus at all, it is officially in the neighboring constellation Andromeda. So the Great Square of Pegasus, which is really a rectangle, probably should be called the Great Triangle of Pegasus. So much for the geometry discussion.
The "Summer Triangle" is
Still With Us - Even in Early AutumnDuring early autumn evenings, as the sun goes down, and darkness begins to take over , look overhead for the first stars that become visible. They will probably be 3 bright stars that form a distinctive triangular pattern. It is a landmark of summer, still visible in early autumn, called the Summer Triangle. The 3 stars which form this pattern are Vega, Deneb and Altair. Each of these stars is actually part of a different constellation. Vega is west-most of the three and is part of the small constellation Lyra. Deneb is north-most and is at the top of the "Northern Cross", or officially called "Cygnus" (the Swan). Altair is south-most and part of the constellation Aquila.
Vega is the brightest of the three stars. Vega is "only" 26 light years away. It is so bright mostly because of its closeness. It is actually a relatively small star, about the size of our sun. Altair is even closer. It is "only" 17 light years away. Deneb, on the other hand, is a supergiant, with a diameter hundreds of times bigger than the other two. Deneb is 1800 light years away!. It is one of the furthest stars we can see with the unaided eye. Its size and brightness are so immense that even at its great distance, it appears to us almost as bright as Vega.
One more interesting fact about Vega. It has an important role in our future. In about 12,000 years the Earth will have changed its angle so that Vega will be virtually directly above our north pole. It will then be our North Star. (See Star Facts article for June, 1995, "There Will Come a Time When We No Longer Have a North Star" for further explanation)
The Moons of JupiterLike a string of pearls, the four largest moons of Jupiter appear in a diagonal line that crosses the giant planet. During October, 1995, Jupiter is low in the southwestern sky right after nightfall and it sets soon after; so look quick. You can't miss it. It is very bright! With a low to medium power eyepiece on a telescope, the moons and planet make a spectacular sight.(See Calvin Hamilton's "Views of the Solar System" for more details about Jupiter's moons).
Not all of these moons are always visible. At various times only three or even two can be seen, as the moons circle behind or in front of the planet. Their positions change visibly from night to night. Make a diagram of the moons' positions one night, then look at them the next night. Notice the dramatic change in positions.
The Disappearing Rings of SaturnDuring October, 1995 Saturn is well up in the southeast by 9:00 p.m. daylight saving time. It's highest around midnight. To find it, locate the Great Square of Pegasus (for help with finding it see entry above titled "The 'Great Square' dominates Autumn Sky"). The two stars with the widest spacing in the Great Square face south. Scan about 1 1/2 fist widths in a southerly direction from the middle of those two stars to find Saturn.
About seven years ago the planet Saturn reached its greatest tilt toward the Earth so that a good deal of the surface of its spectacular rings showed to us. Even small telescopes revealed a magnificent view of the rings. Since then, its angle relative to us has been straightening. In 1995 and 1996 the angle of the rings becomes edge-on to Earth on three separate occasions - May 22, 1995; Aug 10, 1995; and Feb 11, 1996. (See Hubble Space Telescope Image of Saturn Ring-Plane Crossing taken Aug. 10, 1995). Since the rings are believed to be only about 1 mile thick, the edge-on view causes them to disappear from view. Although this is not good for ring watching, it is good for viewing the moons and surface of Saturn. In about seven years from now Saturn will again reach its greatest tilt toward Earth and the rings will once again present a spectacular sight.
The Full MoonThe next full moon occurs on the night of October 8, 1995. The moon is full when it is on the opposite side of the Earth from the sun, so that the part of the moon that faces us also faces the sun. Therefore, at the time of a full moon, the moon rises in the east at the same time that the sun sets in the west.
The best times to view the moon with binoculars or telescope is definitly not around the times of a full moon. It is during the times when the moon is in the crescent to half moon shape. It is at this time that the shadows on the moon are the longest, making the craters and mountains on the moon more visible and three dimensional. The best place to look is around the areas where the light and dark sides of the moon meet. This dividing line is where sunset or sunrise is occuring on the moon, and shadows are the longest.
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