WHAT'S UP there DOC

- a guide to current sights and events in the evening sky

Updated for the month of: April, 1996

Rare Chance to See Mercury

During the period of about April 12 through May 2, 1996, from mid-northern latitudes, the planet Mercury makes a significant showing low in the western sky, about 30 minutes after sunset. It is highest from the horizon after sunset on April 23, 1996.

Mercury is the closest planet to the Sun. Its orbit is on an inside track to that of Venus and Earth. Therefore, from Earth, Mercury never appears far from the Sun, and it is only seen shortly after sunset or just before sunrise. It is usually difficult to see because of the Sun's glare during dusk and dawn. However, during this upcoming period, the ecliptic, the apparant path on which we see the planets cross the sky, makes a particularly steep angle with the horizon at the same time that Mercury is furthest from the Sun from our vantage point. This results in Mercury being higher after sunset than it normally is and provides an excellent opportunity to see it.

Don't confuse Mercury with the currently extremely bright planet Venus, which is also in the western sky after sunset, but higher.



Do the Days Seem to Be Getting Longer Faster

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 in Spring and Autumn and are least in summer and winter.



A Red Giant, 25 Times Bigger Than Our Sun!

The star Arcturus, in the constellation Bootes, appears low in the east as dusk turns into darkness during April. It passes almost overhead around 1:00 a.m.. The easiest way to find it is to follow the curve of the handle of the Big Dipper, backward from the bowl, and "arc to Arcturus".

Arcturus is a red giant, a cooling sun nearing its death. It is the third brightest star in the sky. In its bloated last stages of existence Arcturus has swollen to a diameter of about 25 times the size of our Sun's. It lies about 36 light years away. Its orange-red color is distinct with binoculars.



See Meteor Shower in April

One of the oldest meteor showers known, the Lyrid shower, returns for its yearly visit on the night of April 21/22. The Lyrids is not one of the most active showers, it normally produces only about 10 to 15 meteors per hour (one every 4 to 6 minutes) at its peak. However, it can occasionally and unexpectedly produce a lot more. In 1982 it produced nearly 100 meteors per hour. The meteors will appear to emanate from the constellation Lyra, from which it is named, which rises around 10:30 p.m. in the east and the meteors will travel toward the top of the sky or westward.

Meteor showers occur at the points on the Earth's orbit in which it passes through the path of a disintegrated comet, a comet that has broken up into tiny pieces that now fill the path in which the comet once traveled.

The best time to see a meteor shower is after midnight (see Star Facts article for August, 1995 for explanation). The best way to see it is to lie down on a blanket or lawn chair, relaxing and looking up at the sky, without magnification.

Though April 21/22 is the peak of the Lyrids, increased meteor activity will be visible from about April 16 to April 25.



Eclipse of the Moon on April 3, 1996

On April 3, 1996, Europe, most of Africa and the eastern part of South America will see a total eclipse of the Moon. Those watching from the east coast of North America will see the Moon fully eclipsed as it rises. Those west of the Mississippi will not see the eclipse.

An eclipse of the Moon occurs when the Earth gets in between the Moon and Sun and casts its shadow on the Moon. Even during an eclipse, the moon can be seen as a dark red glow. This is the portion of the Sun's light that is bent by the Earth's atmosphere as it passes Earth and strikes the moon.



The Lion is Here!

As darkness falls during April, the constellation "Leo, the Lion" appears high in the southeastern sky. Appearing as a Sickle, or backward question mark, Leo is highest around 9:00 p.m. in the southern sky, almost overhead. The bright star Regulus, known as the heart of the Lion, is at the bottom of the handle of the Sickle. Regulus is about 85 light years away. It is part of a double star system, two stars in each other's gravitational pull, rotating around each other. Its faint companion can be seen with a good pair of binoculars or a small telescope.

If you look carefully and use your imagination you can actually see a lion. The curved part of the Sickle forms the head, looking toward the west. The bright star Regulus is the chest. The rest of the body, tail and hind leg stretch out toward the east.



Jupiter, a Treat for Night Owls

For those of you who go to bed very late, or get up very early during April, 1996, the largest planet of them all, Jupiter, provides a treat in the middle night to early morning sky. Rising around 1:00 a.m., in the east, Jupiter is easily seen by 2:00 a.m. or 3:00 a.m. low in the southeast. It reaches its highest point, due south, just before dawn. You can't miss it. It's very bright.

Take a look through a telescope and you get an even better treat. Those four (or sometimes three or two) bright objects on either side of the giant planet in a linear alignment are Jupiter's four largest moons. What happened to the others when there are only three or two? They are not visible for a few hours because they are passing behind or in front of the planet.

As you look at Jupiter and it's four largest moons with a telescope, imagine Galileo's amazement about 300 years ago when he used the first astronomical telescope to look at Jupiter, and became the first human being to see the moons of another planet.



Giant Question Mark in Northern Sky
Can Save Your Life

As darkness falls in April the Big Dipper appears as a somewhat tipped question mark in the northern sky. The Big Dipper is the most recognized shape in the sky. From most of the northern half of the Earth it never sets! It just goes around the North Star, making one giant circle each 24 hours. Even though the Big Dipper is one of the largest star shapes in the sky, it is only part of a still larger constellation called Ursa Major, or Big Bear (good luck seeing a bear - the people who named it must have been smoking some of that funny stuff). A recognizable shape, such as the Big Dipper, that is part of one or more constellations is called an "asterism".

The Big Dipper can save your life if you are ever lost at sea or in a wilderness area, by providing a way to determine which direction is north. The two stars at the dipper end (not the handle) are called the "pointers". They point to Polaris, the North Star. If you follow an imaginary line extending from the pointers 3 fist widths across the sky (the width of your fist with arm extended) in the direction of the open side of the dipper, you come to the North Star. It is not a bright star, but it is the brightest in that part of the sky.



Sirius, Brightest Star and Champion Twinkler

Sirius is the brightest star visible from Earth. Only some of the planets and the Moon can outshine it in the night sky (don't confuse Sirius with the even brighter planet Venus which is currently visible after sunset in the southwestern sky). Sirius is known as the "Dog Star" because it is in the center of the constellation Canis Major, or Great Dog. As darkness comes in April it is the first star visible low in the southwestern sky. It continues moving in a westward direction as it gets lower and sets in the west around 9:00 p.m.

Sirius is probably the star that inspired the nursery rhyme song "Twinkle, Twinkle, Little Star". It twinkles profusely, "...like a diamond in the sky...". The lower in the sky it is when you observe it, the more dramatic its sparkle, as its bright light passes through a thicker layer of Earth's air. The reason Sirius is the brightest star of all, has more to do with its relative proximity to Earth, than its size or intrinsic brightness. Sirius is "only" 8.6 light years away from Earth, the fifth closest star. It has a diameter of 1.8 times that of our sun.

Sirius is part of a double star system, two stars in each other's gravitational field, rotating around each other. It has a small, faint, elusive companion called Sirius B, or the "Pup". It takes Sirius and the Pup 50 years to rotate around each other. The Pup is a white dwarf star - a "dead" star that has run out of hydrogen fuel to burn and has collapsed in on itself, shining only because its temperature remains high. As it cools it will eventually become a black dwarf - dead, cold and invisible from Earth. The Pup is an incredibly dense object thought to be only 30,000 kilometers in diameter, with each cubic inch of this star weighing over 2 1/2 tons!



The Great Nebula in the Hunter's Sword

Hanging underneath the left-most star in the line of three bright stars that form the famous "belt" of the mythical Orion the Hunter (found in the southwest sky as darkness falls in April), is a dim, diagonal, somewhat fuzzy line of light. This is known as the Hunter's Sword. On clear nights three dim stars in the sword are visible with the naked eye.

Look at the sword with binoculars and you see three pairs of stars, the middle pair appearing to glow in a fog-like area. With a low or medium power eyepiece on a telescope you see a celestial wonderland of glowing swirls and streamers of interstellar gas, with brighter concentrations and dark, black regions. Glowing inside the misty mass are several bright stars, shining like beacons in the fog. You are seeing one of the most beautiful and exciting sights in the heavens. This is a nebula, known as the "Great Nebula in Orion", also classified as M42. (See beautiful time-exposure photo of the Orion Nebula on Jason Ware's website). It is a star nursery containing newly formed "baby" stars. Still others are being created as we look at it. It is a star cluster in the making. See Star Facts article for January, 1996, "How and Where Stars Are Born" for more complete explanation.



Betelgeuse, the Red Supergiant

Above and to the left of the line of three bright stars that form the famous Orion's Belt (found in the southwest sky as darkness falls in April), is a bright reddish star named Betelgeuse (popular pronunciation: "beetle-juice"). Betelgeuse is a red supergiant. It is an example of a dying star that has become bloated in its last stages of life.

Betelgeuse, which is about 300 light years away, is so large that if it were our sun it would engulf the planets Mercury, Venus, Earth and Mars. We would be inside it! It is a variable star, unstable in size, that fluctuates erratically in brightness during a period of about 6.4 years.

It is interesting to contrast the reddish color of Betelgeuse with Rigel, another supergiant star in Orion. Rigel, about 900 light years away, is located below and to the right of Orion's Belt. It is a blue supergiant, on the other side of the color spectrum of stars from Betelgeuse. The color difference is dramatic when seen with binoculars. Bluish stars are the hottest. Reddish stars are the coolest.



Venus Gets Brighter as it Shrinks!

Between January and June 1996, the planet Venus presents a spectacular sight in the southwestern sky during the first 1 to 2 hours after sunset. Other than the Sun and Moon, Venus is the brightest object in the sky. It will continue getting brighter during the next few months as it races around the Sun on an inside track to the Earth's orbit, and "catches up" to us in June, 1996. (See "Solar System Live" website to see relative positions of the planets, click on "inner planets", blue circle is Earth, white circle is Venus).

Because Venus, our next door neighbor in space, is closer to the Sun than Earth is, we see it going through phases that are similar to the Moon's phases. When it is on the opposite side of the Sun from Earth we see it far away but full-face, a "full Venus". When there is a 90 degree angle between Earth, Sun, and Venus, as is the case on April 1, 1996, we see a brighter "half Venus". As Venus catches up to Earth in its orbit and comes close to lapping us on its inside track, we see an even brighter "crescent Venus". So Venus gets brighter as it comes closer to Earth, even though the part that we see lit up is shrinking.

To see the phases of Venus you need a good pair of binoculars or a small telescope. Keep an eye on it between now and June, and you will see an exciting progression of changes.



The Full Moon

The next full Moon occurs on the night of April 3, 1996. That will also be the time of a lunar eclipse seen in totality in Europe, Africa, and the eastern part of South America, and in the eastern part of the United States just as the Moon is rising.

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 about the same time that the Sun sets in the west.

The best times to view the moon with binoculars or telescope is definitely 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, called the "terminator", is where sunset or sunrise is occurring on the Moon, and shadows are the longest.

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Send suggestions, astronomy tips, corrections or comments to Pete Harris
via e-mail at odyssey@ccnet.com. Pete is also the creator of the website
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