April and May Observatons

April and May have been quite challenging for me. We had some major life events that I won't get into here happen and in May, I have had a horrible respiratory virus and a skin infection. I couldn't get the material that I sketched on three observations to scan, but today I finally was able to use the old scanner. We are going to buy a new scanner/copier/printer at some point, just now sure when.

APRIL 5th and 6th, 2009
On April 5, 2009 I was able to view the following objects. I got in what was to be my last view until fall of M42 and it was really stellar that night. I used a UHC NB Filter and the shape of the nebula really came out. I took the filter out and the trapezium. Conditions were good enough to see the E star tonight and at 240x I could see both the E and F stars tonight. By the time I finished though forty-five minutes later at 10:00p.m. the E and F stars were really hard to see.

My next object was M-53, a globular cluster. I went to Denobola and then to CD 6 and then to CB 27. From CB 27 I went to CB 36 and then to Alpha CB and then east and M53 was easily seen. At 92x in the 13mm Stratus M53 appears as a faint fuzzy. The waxing gibbous moon I am sure is not helping with this observation. There are two stars close together to the northwest with a third star some distance to the left. A tight and bright core is clearly evident with diffusion around it as one looks out past the core. The core is a third of the halo and with averted vision I can see some lanes of stars coming out from the core.


























April 6 was my double star posting that comes before this one.

Also on April 6th I observed the globular cluster of M3. Got there in a round about way. Used the Telrad to go to Arcturus in the constellation Bootes. From there I jumped to Muphrid and then jumped up to 6 Bootes. From 6 Bootes I went northeast diagonally to an elongated triangle or quadilateral. The northwest star up diagnonal shoed M3 sticking out and easy to see. I will have to return to his object when there is no moon to really grasp its full intensity. At 184x a strong core stands out with hundred of stars moltled. Averted vision brings out tendrils of stars which I tried to capture in my sketch. Also, using averted vision to the southwest brings out the most detail while observing this wonderful object. I have to say that in many ways I think I like M3 better than M13 in Hercules. Then again, I haven't looked at M13 since last summer/early fall.



























APRIL 12th and 13th, 2009
On the night of April 12th and the morning of April 13th I was able to get some observing time in. I really don't like summer observing because of the issue of daylight savings. It's between 10:00p.m. and 11:00p.m. before I can start and if I want to observe on a work night that makes it difficult. Guess I need to learn to take some naps.

This night my first object that I observed was the galaxy M-91. I was using the eight inch dob with the telrad and my 21 and 13mm Stratus. I used the telrad to go to Vindematrix and then went west to a double (see the Sky Pocket Atlas). The nI went up diagonally to a star then over to a sideways triangle asterism whose top star is a double (appears to be). Next I went over to three stars that are north-south or up-down and then over from the middle star almost due east. I ran into M-91 and confirmed it by going to M88. M91 is a fuzzy blur at 92x and it appears face on. No mottling or structure is visible and the edge is diffused. The core is bright, small and tight. Hyperventalating helps to see the structure on this galaxy and its shape. No birght or dark lanes are visible. It does appear to have a tie fighter appearance to me and that is reflected in the sketch.




























Starting around 12:09 a.m. I left M-91 and went and observed both M89 and M90. To find these I started at Vindematrix and jumped to the double next to it; see the SkyPocket Atlas on pg, 45. Then I went diagonally northeast to two stars next to each other and then down pass M60 and M59 to M58. From M58 I then went up to M89 and M90. M89 shows more details and has a very bright core with some mottling of dark and light. No lanes or hints of lanes could be seen, just some hints. M90 showed a bright core with diffusion of brightness around the core with hints of shape. M90 seems to sit almost northwest to southeast and is more edge on than M89. M89 appears to me to be face on.




















































After spending time with M89 and M90 I went to take a look at M49. Again I went to Vindemiatrix and hopped over to Rho Virgo which is an asterism of a triangle with Rho in the middle. I then went diagonally SE to another triangle asterism where I saw NGC 4526, a galaxy and observed it, but did not sketch it. Should of, perhaps next time. From NGC 4526 I sent north and then east to easily see M49. M49 is a large ellipitical galaxy with a bright center core surrounded by a halo with no details visible. No structure outside of the size and shape was visible either.



























Here are my notes on NGC 4526: NGC 4526 is a lenticular barred galaxy that sits between two stars locaed and easily seen. NGC 4526 sits between those two stars that form a part of a triangle. It has a bright central core, white and roundish/circular with a halo surrounding it. Immedietly to the north is a star or a fainter galaxy perhaps (it is a star not a galaxy like M51)? NGC 4526 is similar to M51 in my opinion because of the star that seems connected to it. No matter what this is a nice looking object. The halo from NGC 4526 extends to just below the star -- the star could be a foreground (my guess) or a background star.

Next I came upon M64, the Black Eye Galaxy. I used the telrad to go to Vindermaitrix and then to Alpha Coma B by star hopping up to an asterism of three stars. From here I went southeast and M64 was very easy to find, it was straight down from the third star. At 92x M64 is a face on with a bright core and mottling of darkness to the northeast. There is a line that runs west to east of brightness from the western edge to the core. Definite hints of lanes are visible on this beauty. A wonderful item to observe. I did a sketch at 92x and at 184x.





















































My next observation came on April 29th and I observed several items, but only officially recorded one item, but it was one that has eluded me for sometime. Tonight I was able to bag M109, a galaxy in Ursa Major. I decided that even with a waxing crescent to take a shot at M109. The moon is almost down to the horizon (heading there quickly) and using the telrad, I went to Phelda. From Phelda I went to the three stars in a line that are south-west of Phelda. Using averted vision I spotted M109. It is rather large in shape and because of that, it is very faint. I have to wait until periods of seeing improve but in good periods I can make out a distinct core with a lot of haze and faint fuzziness around it. I returned after the moon set to sketch it and M109 gave up a few more details.



























MAY 15th AND 16th, 2009

My next session was on May 15 and May 16, 2009. My first object was NGC 4147, a globular cluster in Leo. I used the telrad to Denebola and then went to CB 6 from which I went up to an astermism of three stars that form a triangle with the top star on the left middle, and the two other stars going up diagonally to the upper right and lower left. From the top star in the asterism (upper right from the middle or point star) I worked my way up and in the 21mm Stratus EP the golbular stuck out as a fussy. No mottling or stars are present at 57x , only a fuzzy ball. At 240x using the 5mm Hyperion I could make out the shape of the core with fuzziness around it. At 92x in the 13mm Stratus I got my best views. The core is bright and visible though no stars are visible on the core. Averted vision is best to distinguish size of this small globular. A nice change to the galaxies in the area. I'll add my image later on this but I do have a sketch.

On May 16 I went Spica and then went to Virgo 49. From V 49 I went to two stars down diagonally to the right, next to NGC 4802 then up to the star above it. From here I went to an astermism of a triangle with a third star on the left edge. From there I star hopped to three stars in a row then M104 came into view. At 55x I could make out the distinct shape and a bright core. At 240x conditions would only show a bright core. 92x shows both the shape of the galaxy, and the dark line down the center. This is a very fat and elognated galaxy. At first I could see only from the dark line up to the top half, then with averted vision the bottom half came into view. Both averted vision and direct vision brings out the details on this wonderful galaxy.


























My next object was M101 around 12:44a.m. M101 is an easy object to get to, but very hard to see. I've missed it at least twice before. Tonight I used the telrad to get to Mizar and Alcor and then star-hopped on the four bright stars leading up up from the Mizar/Alcor pair. I went pass 83 UMa and the fourth star has three stars in a line next to it. The middle star in that line has a birghter star next to it/above it. That star forms another line of three stars and avoe these are three more. By connecting them they make a box. From that top corner star in the last in the line, follow out two more stars then down and you'll see M101. It is very important to be dark adapted when going after this galaxy because it is so big that the light is dispursed. I could discern a weak and faint core. No stars are visible or lanes at first. With averted vision I can discern the size of this face on galaxy and it is huge! By continuing to observe I could eventually discern lanes and some dust in them.
I have to say that if one is not experienced in seeing and finding really faint fuzzies than M101 is one to wait on until one has more experience. The core shows dull at times and then almost like a distant star with averted vision. This is one where a dark site would really help one to see this object in a lot of detail.



























M4 was my next object. I used the Telrad to Antares, a beautiful orange star) and I looked in the finder and due west I could easily see M4. M4 is a wonderful globular cluster where many and various colors are present. Many stars are visible and at 55x it shows stars as individuals and with nebulosity around them. At 240x M4 shows the bright stars of the core and details in patterns. 92x shows the best details again and the shape of this cluster is clearly evident. This is not a typical globular in terms of a tight ball. There are stars that are around the center portion of this globular that look like they are part of the globular but farther out.


























M80 Globular Cluster was my final item on the night of May 16/17, 2009. I used the telrad to go to Antares again and then to O Scorpius. From here I went to two diagonal stars that lead to M80. Another way was Antares to a triangle asterism below IC 4601 to a star below the triangle asterism. Then work back to the top star that is diagonal. Unlike M4, M80 is a tight and ball shape globular cluster, more typical of others I've seen. M80 has a bright central core with some stars showing on the edges at 92x. At 240x, M80 still shows a bright inner core but far more stars are no visible. A very fun globular to view.

Resensi Buku : Menjelajah Tata Surya

Format: Paperback, 302 halaman
Penerbit: Kanisius
Pengarang: A. Gunawan Admiranto
Harga : Rp.60.000,00
isbn: 9789792119
Tanggal Publish: 31 Mar 2009

Alam semesta telah sejak lama memukau manusia dengan keindahannya dan juga misteri di dalamnya. Dan perjalanan sejarah manusia membuktikan kalau keingintahuan untuk menyingkap misteri di alam semesta telah membawa manusia dalam perjalanan panjang penelitian dan penjelajahan untuk mengungkap satu demi satu misteri yang menyelimuti alam maha luas.

Dari penglihatan akan gerak benda langit dari Bumi sampai penjelajahan telah dilakukan oleh manusia demi menyingkap misteri itu. Buku karangan Gunawan Admiranto, :Menjelajah Tata Surya�, mencoba membawa kita mengenal ruang lingkup Tata Surya dimulai dari sejarah perkembangan konsep Tata Surya sampai dengan anggota keluarga yang ada di tepian luar Tata Surya.

Perjalanan di tata Surya diawali dari Matahari kemudian ke setiap planet dan diakhiri dengan keberadaan obyek-obyek di tepi luar Tata Surya yang dikenal sebagai obyek Kuiper. Keindahan Tata Surya dipaparkan dengan bahasa yang sederhana untuk dipahami. Satu per satu planet dikupas sampai ke proses yang terjadi di dalamnya. Dan tak lupa definisi planet yang terbaru pun disertakan dengan mengacu pada peristiwa mengapa Pluto bukan planet lagi. Kehadiran klasifikasi baru planet katai juga dijelaskan dengan baik.Buku ini sangat baik untuk para pelajar yang ingin mengenal lebih dekat Tata Surya dan semua yang ada di dalamnya.

Namun bagaimanapun gamblangnya Tata Surya dijelaskan lewat penjelajahan ini, penjelajahan sesungguhnya dari para ilmuwa belumlah berakhir. Masih ada segudang misteri yang masih menanti untuk disingkapkan.

Sumber : langitselatan.com

Buku ini sangat disarankan bagi pecinta astronomi, khususnya para pemula. Saya pernah menggunakan buku ini (edisi lama) dan banyak sekali hal yang dapat dipelajari. Selamat belajar.

Binary Stars

Looking through a telescope at the stars there is very little information we can gain from them. To be sure, we know what color they are and we can see that some are more luminous than others. If we use a spectrograph we can tell what elements they are made up from. From these facts alone, it is difficult to tell just how much mass they contain.

By looking at pairs of stars that orbit one another we can try to answer the question, how much mass do the stars have?

Binary stars can be of two fundamental types:

• Visual Binaries
• Optical Doubles

Alberio (Visual Binary)
Visual Binaries are stars that are clearly gravitational associated with one another. They orbit each other around a common center called the barycenter. Visual binaries can be seen optically through a telescope. Only a small portion of binary stars are visual binaries. In order to see a visual binary, the stars must be separated by fairly wide distances, and the orbital periods are usually very long.

Optical Doubles are stars that appear to lie close together, but in fact do not, they only appear to us from our earthly observation to be close together. One of the stars in the pair is actually behind the first star and very far away. The stars of an optical double are not gravitationally bound.

William Herschel began looking for optical doubles in 1782 with the hope that he would find a measurable parallax, by comparing a close star to the more distant star in an optical double.
Herschel did not find any optical binaries, but he did catalog hundreds of visual binaries. In 1804 Herschel had so many measurements of visual binaries that he concluded that a pair of stars known as Castor were orbiting one another. This was an important discovery, because it was the first time observational evidence clearly showed two objects in orbit around each other outside of the influence of our own Sun and Solar System.

Spectroscopic Binary
It is also possible to detect binary stars using a spectroscope. If two stars are orbiting each other they will both produce a spectrum. If the stars are close to being the same brightness it is possible to see different spectral lines from both stars. These stars are of particular interest because it can be used to determine the radial velocity of the orbit of the two stars. Stars appear red shifted when receding away from the earth and blue shifted as they approach. This effect is caused by the Doppler effect which distorts arriving light waves from the stars depending on the direction if their motion. A Spectroscopic binary will alternate between blue and red shifted spectral lines.


Spectroscopic binaries are not detectable if we are seeing the star head on because no Doppler shifts would be present in the spectrum. If the Doppler shifts are present in a single line of the spectrum, we are seeing the light from only one star and we call this a single-line spectroscopic binary. If we can see the light from both stars the Doppler shifts will alternate, split and merge depending on the positions of the two stars in their orbits. This is called a double-line spectroscopic binary.

One very important detail, we do not know how the orbits of the two stars are inclined to earth. This inclination could be any angle, for that bit of information we have to go back to visual methods in order to see the individual stars to determine the inclination of their orbits relative to earth. Even so we can not for certain determine the true inclination of the orbit so our mass calculation is only a lower limit to the masses of the two stars.

Radial velocities permit astronomers to compute the total mass for the two stars, they do not provide the masses for the individual stars and other methods must be used to make that determination

Eclipsing Binary
Another type of binary called the Eclipsing binary can be studied. The information gathered can be used to calculate the individual stellar masses and the diameters of the individual stars. It is rare to find two stars in orbit around one another to have orbital inclination where the stars pass in front of one another to form one point of light as seen from earth.
When the orbital inclination if the eclipsing binary is edge on to earth, the stars will seem to pass in front of one another as they orbit, when the light from the brighter star is eclipsed we will see a deep decline in the amount of light received from the star (6/25/95 in Figure 1) we call this primary minimum, also when the light from the dimmer star is blocked by the brighter the light received declines again, but not so deep and we call this secondary minimum (see 6/9/95 in Figure 1) , otherwise we are able to collect some or all of the light from both stars.


The pattern of these light changes is called a light curve and the data for it gathered by the use of a photometer, making periodic measurements until the eclipsing binaries produce a complete orbital cycle.

We use the mass vs. luminosity relationship to determine what the difference is between the individual masses, then using the mass of the entire system calculated from the radial velocity information, we can determine what the individual masses of the two stars should be. The photometeric data removes some of the uncertainty in regard to the inclination because the shapes of the light curves will be different for a partial eclipse than for a total eclipse.
ALGOL is one of the best known and most studied eclipsing binary stars. ALGOL is normally about 2.3 magnitude, but every 10 hours or so it will dim to about 3.4 magnitude, in other words ALGOL becomes 68% dimmer. I suspect that humanity has known about ALGOL's behavior for quite some time, since the Arabic name of ALGOL means "Demons Head", and ALGOL is associated with the severed head of Medusa. ALGOL is often referred to as the winking eye of the demon.

An eclipsing binary occurs when the orbital plane of the binary system is exactly When one star passes directly in front of the other, as viewed from Earth, we seen an eclipsing binary perpendicular to the plane of the sky.

Dwarf Nova or Recurrent Nova


When an otherwise normal star is associated with a white dwarf companion, a type of binary called a recurrent nova, or dwarf nova may occur. The normal star transfers mass onto an accretion disk which forms around the white dwarf. As material falls onto the accretion disk some of the material may be transferred to the white dwarf by turbulence in the accretion disk, this causes a sudden brightening of the white dwarf as the hydrogen is converted into helium.
If enough material from the accretion disk falls onto the white dwarf the hydrogen gas will become compressed and will not immediately fuse until a substantial increase in temperature occurs; the material will suddenly and violently erupt fusing into a runaway fusion reaction and a violent eruption called a dwarf nova occurs which will blow the accretion disk away, but it will not disturb the normal star.


Mass transfer will quickly resume and a new accretion disk will form. The cycle will continue until enough mass is drawn off the normal star to halt the reaction.

Mass transfer in any type of binary system will affect the evolutionary cycle of the two stars. The normal star will burn its fuel more slowly as mass is removed and the star cools down due to less internal heating from gravitational forces. It will also accelerate the evolution of the star receiving the mass, for the same reasons, more mass, more internal heating and the hastening of the fusion process.

If the material transfers very quickly, the gravitational forces will prevent the hydrogen from fusing by compressing it even further until the hydrogen gas becomes degenerate matter. Degenerate matter does not expand due to the increases in temperature so the mass of the white dwarf increases until it exceeds the Chandrasekhar Limit. When this happens the white dwarf will collapse and a type I supernova will occur which may destroy the companion star and the white dwarf changes into a neutron star or a black hole.

Burster
A similar event can occur when a normal star is associated with a pulsar, the energy given off will be mostly X-rays however, and instead of being called a dwarf nova or recurrent nova, it is called an X-ray burster or more simply a burster. We think that as normal hydrogen falls onto the accretion disk it is quickly converted into helium, when the helium reaches a depth of 1 meter, it will explosively convert helium into carbon producing X-rays. The longer the delay in fusing carbon, the larger and more violent the burst will be. The main difference between the recurrent nova and the burster is that the accretion disk will be hotter in the burster because it is already fusing hydrogen into helium, also the burst will produce mostly X-rays instead of visible light.


When a black hole is associated with a normal star, it will produce the same events as an X-ray burster and the only way to be sure that the companion is a blackhole, is when the mass of the compact object is greater than 3 solar masses. This is far too much mass for the companion to be a neutron star. The gravitational forces would cause the collapse of the star beyond the point of the neutrons to support themselves against the force of gravity and the star would collapse to a zero radius creating a black hole.

Calculation of star's properties with binary stars
Types of Binaries

• Visual Binary: Can see both stars and follow their orbits over time.
• Spectroscopic Binary: Cannot separate the two stars, but see their orbit motions as Doppler shifts in their spectral lines.
• Eclipsing Binary: Can separate the stars, but see the total brightness drop when they periodically eclipse each other.

Visual Binaries --> Two stars orbiting about their center-of-mass.


Center of Mass
Two stars orbit about their center of mass.

• Measure semi-major axis, a, from projected orbit & the distance.
• Relative positions about the center give: M1/M2 = a2/a1

Measuring Masses
Newton's Form of Kepler's Third Law:
Procedure:
1. Measure the period, P, by following the orbit.
2. Measure semi-major axis, a, and the Mass Ratio, M1/M2, from the projected orbit on the sky.
3. Solve the equation above and separate Masses.

Problems
We need to follow an orbit long enough to trace it out in detail:

• This can take decades
• Need to work out the projection on the sky

Measurements depend on knowing the distance:

• semi-major axis depends on d
• derived mass depends on d^3

Small errors add up quickly (10% error in distance translates into a 30% error in the mass!).


Spectroscopic Binaries
Most binaries are too far away to be able to see both stars separately.
But, you can detect their orbital motions by the periodic Doppler shifts of the spectral lines:

� Determine the orbit period & size from the pattern of orbital velocities


Problems:
Cannot see the two stars separately:

• Semi-major axis must be guessed from the orbit motions.
• Can't tell how the orbit is tilted on the sky

Everything depends critically on knowing the distance.
Again...

Eclipsing Binaries
Two stars orbiting nearly edge-on to our line-of-sight.

• See a periodic drop in brightness as one star eclipses the other.
• Combine with spectra which measure orbital speeds

With the best data, one can find the masses of the stars without having to know the distance!!!


Problems
Eclipsing Binary stars are very rare.
Measurement of the light curves is complicated by details:

• Partial eclipses yield less accurate numbers.
• The atmospheres of the stars soften the edges.
• Close binaries can be tidally distorted.

However, the best masses are from eclipsing binaries.

Source : many different sites

Soal Latihan : Mengenal Rasi Bintang

Coba kenalilah beberapa rasi bintang yang ada di gambar berikut.

Tips :

• Klik gambar tersebut untuk melihat ukuran penuhnya.
• Beberapa rasi tersebut membentuk suatu pola tertentu yang digunakan sebagai penanda musim

Selamat mencoba

Soal Latihan Astronomi Dasar

Silakan melatih pemahaman Anda tentang Astronomi dari beberapa soal yang saya post-kan.

Selamat belajar.

Soal Latihan Astronomi - 9 Mei 2009

Trivia Quiz:
Coba Anda sebutkan nama objek yang ada di foto berikut!

Why Are Galaxies Smooth?

NGC 2841, a smooth galaxy. Credit: NASA

Look at the disk of any large spiral galaxy, and outwardly it appears smooth, with stars evenly distributed throughout. But when young stars are forming, they are clustered together in dense clouds of dust and gas. So what happens as the galaxy matures to allow for the smooth distribution seen in galaxies like the Milky Way? Using NASA�s Spitzer Space Telescope, an international team of astronomers has discovered streams of young stars flowing from their natal cocoons in distant galaxies. These distant rivers of stars provide an answer to one of astronomy�s most fundamental puzzles.

Astronomers know that the clusters where stars form begin to disappear when their ages reach several hundred million years. A few mechanisms are thought to explain this: some clusters evaporate when random internal motions kick out stars one by one, and other clusters disperse as a result of collisions among the clouds where they were born. Zooming out to mechanisms operating on larger scales still, shearing motions caused by the galaxy�s rotation around its center disperses the clusters of clusters of young stars.

�Our analysis now answers the grand puzzle. By finding a myriad of streams of young stars all over the disks of galaxies we studied, we see that the mechanism for pulling the clusters of young stars apart is shearing motions of the parent galaxy. These streams are the �missing link� we needed to understand how the disks of galaxies evolve to look the way they do,� said team leader David Block of the University of the Witwatersrand in South Africa.

Crucial to this discovery was finding a way to image previously hidden young stellar streams in galaxies millions of light-years away. To do this the team used high-resolution infrared observations from the Spitzer.
Using infrared rather than visible light to look at the galaxies allowed the group to pick out stars at just the right age when the stars are just starting to spread out from their clusters.

Credit: NASA/ Spitzer team

�Spitzer observes in the infrared where 100-million-year-old populations of stars dominate the light,� noted co-author Bruce Elmegreen, from IBM�s Research Division in New York. �Younger regions shine more in the visible and ultraviolet parts of the spectrum, and older regions get too faint to see. So we can filter out all the stars we don�t want by taking pictures with an infrared camera.�

Infrared is also important because light in this part of the spectrum can penetrate the dense dust clouds surrounding the clusters where stars form.

�Dust blocks optical starlight very effectively,� said Robert Gehrz of the University of Minnesota, �but infrared light with its longer wavelength goes right around the dust particles blocking our view. This allows the infrared light from young stars to be seen more clearly.�

But even when the images are taken in the infrared, they are still dominated by the light from the smooth older disks of galaxies, not the faint tracks of young dispersing clusters. Special mathematical manipulations were needed to pick out the clusters, whose faint tracks can still be seen precisely because they are not smooth.

Team member Ivanio Puerari of the Instituto Nacional de Astrofisica, Optica y Electronica in Puebla, Mexico used a technique invented by mathematician Jean Baptiste Fourier in the early 1800�s. The technique is effectively a spatial filter that picks out structure on the physical scale where star formation occurs. �The structures cannot be seen on the original Spitzer images with the human eye,� noted Puerari.

�The combination of the Fourier filtering and infrared images highlighted regions of just the right size and the right age. To then unveil so many star streams in the disks of galaxies was unimaginable a year ago. This discovery continues to highlight the enormous potential of the Spitzer Space Telescope to make contributions none of us could have dreamed possible,� commented Giovanni Fazio from the Harvard-Smithsonian Center for Astrophysics, project leader for the Spitzer Infrared Array Camera team used to take the pictures, and co-author of the discovery.

�Galileo, as both astronomer and mathematician, would have been proud. It is a wonderful interplay between the use of astronomical observations and mathematics and computers, exactly 400 years since Galileo used his telescope to examine our Milky Way galaxy in 1609,� Fazio said

Source: Spitzer
Cited from : Universe Today