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Solar System

The Solar System^[a] comprises the Sun and its planetary system of eight planets,^[b] as well as a number of dwarf planets, satellites(moons), and other objects that orbit the Sun.^[c] It formed 4.6 billion years ago from the gravitational collapse of a giant molecular cloud. The vast majority of the system's mass is in the Sun, with most of the remaining mass contained in Jupiter. The four smaller inner planets,Mercury, Venus, Earth and Mars, also called the terrestrial planets, are primarily composed of rock and metal. The four outer planets, called the gas giants, are substantially more massive than the terrestrials. The two largest, Jupiter and Saturn, are composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are composed largely of substances with relatively high melting points (compared with hydrogen and helium), called ices, such as water, ammonia and methane, and are often referred to separately as "ice giants". All planets have almost circular orbits that lie within a nearly flat disc called the ecliptic plane.

The Solar System also contains a number of regions populated by smaller objects.^[c] The asteroid belt, which lies between Mars and Jupiter, is similar to the terrestrial planets as it mostly contains objects composed of rock and metal. Beyond Neptune's orbit lie theKuiper belt and scattered disc, linked populations of trans-Neptunian objects composed mostly of ices. Within these populations are several dozen to more than ten thousand objects that may be large enough to have been rounded by their own gravity.^[10] Such objects are referred to as dwarf planets. Identified dwarf planets include the asteroid Ceres and the trans-Neptunian objects Pluto, Eris, Haumea, andMakemake.^[c] In addition to these two regions, various other small-body populations including comets, centaurs and interplanetary dustfreely travel between regions. Six of the planets, at least three of the dwarf planets, and many of the smaller bodies are orbited by natural satellites,^[d] usually termed "moons" after Earth's Moon. Each of the outer planets is encircled by planetary rings of dust and other small objects.

The solar wind, a flow of plasma from the Sun, creates a bubble in the interstellar medium known as the heliosphere, which extends out to the edge of the scattered disc. The Oort cloud, which is believed to be the source for long-period comets, may also exist at a distance roughly a thousand times further than the heliosphere. The heliopause is the point at which pressure from the solar wind is equal to the opposing pressure of interstellar wind. The Solar System is located within one of the outer arms of the Milky Way galaxy, which contains about 200 billion stars.

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

Tata Surya

Tata Surya^[a] adalah kumpulan benda langit yang terdiri atas sebuah bintang yang disebut Matahari dan semua objek yang terikat oleh gaya gravitasinya. Objek-objek tersebut termasuk delapan buah planet yang sudah diketahui dengan orbit berbentuk elips, lima planet kerdil/katai, 173 satelit alami yang telah diidentifikasi^[b], dan jutaan benda langit (meteor, asteroid,komet) lainnya.

Tata Surya terbagi menjadi Matahari, empat planet bagian dalam, sabuk asteroid, empat planet bagian luar, dan di bagian terluar adalah Sabuk Kuiper dan piringan tersebar. Awan Oort diperkirakan terletak di daerah terjauh yang berjarak sekitar seribu kali di luar bagian yang terluar.

Berdasarkan jaraknya dari Matahari, kedelapan planet Tata Surya ialah Merkurius (57,9 juta km), Venus (108 juta km), Bumi(150 juta km), Mars (228 juta km), Yupiter (779 juta km), Saturnus (1.430 juta km), Uranus (2.880 juta km), dan Neptunus(4.500 juta km). Sejak pertengahan 2008, ada lima objek angkasa yang diklasifikasikan sebagai planet kerdil. Orbit planet-planet kerdil, kecuali Ceres, berada lebih jauh dari Neptunus. Kelima planet kerdil tersebut ialah Ceres (415 juta km. di sabuk asteroid; dulunya diklasifikasikan sebagai planet kelima), Pluto (5.906 juta km.; dulunya diklasifikasikan sebagai planet kesembilan), Haumea (6.450 juta km), Makemake (6.850 juta km), dan Eris (10.100 juta km).

Enam dari kedelapan planet dan tiga dari kelima planet kerdil itu dikelilingi oleh satelit alami. Masing-masing planet bagian luar dikelilingi oleh cincin planet yang terdiri dari debu dan partikel lain.

Bimasakti

Bima Sakti (dalam bahasa Inggris Milky Way, yang berasal dari bahasa Latin Via Lactea, diambil lagi dari bahasa Yunani Γαλαξίας Galaxiasyang berarti "susu") adalah galaksi spiral yang besar termasuk dalam tipe Hubble SBbc dengan total masa sekitar  massa matahari, yang memiliki 200-400 miliar bintang dengan diameter 100.000 tahun cahaya dan ketebalan 1000 tahun cahaya.^[1] Jarak antara matahari dan pusat galaksi diperkirakan 27.700 tahun cahaya. Di dalam galaksi bimasakti terdapat sistem Tata Surya, yang didalamnya terdapat planet Bumi tempat kita tinggal. Diduga di pusat galaksi bersemayam lubang hitam supermasif (black hole). Sagitarius A dianggap sebagai lokasi lubang hitam supermasif ini. Tata surya kita memerlukan waktu 225–250 juta tahun untuk menyelesaikan satu orbit, jadi telah 20–25 kali mengitari pusat galaksi dari sejak saat terbentuknya. Kecepatan orbit tata surya adalah 217 km/d.

Di dalam bahasa Indonesia, istilah "Bimasakti" berasal dari tokoh berkulit hitam dalam pewayangan, yaitu Bima. Istilah ini muncul karena orang Jawa kuno melihatnya susunan bintang-bintang yang tersebar di angkasa jika dihubungkan dan ditarik garis akan membentuk gambar Bima dililit ular naga maka disebutlah "Bimasakti". Sementara itu, masyarakat Barat menyebutnya "milky way" sebab mereka melihatnya sebagai pita kabut bercahaya putih yang membentang pada bola langit. Pita kabut atau "aura" cemerlang ini sebenarnya adalah kumpulan jutaan bintang dan juga sevolume besar debu dan gas yang terletak di piringan/bidang galaksi. Pita ini tampak paling terang di sekitar rasi Sagitarius, dan lokasi tersebut memang diyakini sebagai pusat galaksi.

Diperkirakan ada 4 spiral utama dan 2 yang lebih kecil yang bermula dari tengah galaksi. Dan dinamakan sebagai berikut:

• Lengan Norma
• Lengan Scutum-Crux
• Lengan Sagitarius
• Lengan Orion atau Lengan Lokal
• Lengan Perseus
• Lengan Cygnus atau Lengan Luar

http://id.wikipedia.org/wiki/Bimasakti

Milky Way

The Milky Way is our home galaxy, containing our Solar System, where our planet, Earth, resides.^{[12][13][14][nb 1]} Its name "milky" is derived from its appearance as a dim glowing band arching across the night sky in which the naked eye cannot distinguish individual stars. The term "Milky Way" is a translation of the Classical Latin via lactea, from the Greek γαλαξίας κύκλος (pr. galaxías kýklos, "milky circle").^[15][16][17] From the Earth, the Milky Way appears like a band because its disk-shaped structure is viewed from within the Galaxy.Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. In the past, astronomers thought that all of the stars in the universe were contained inside of the Milky Way. Following the 1920 Great Debate between the astronomers Harlow Shapleyand Heber Curtis,^[18] observations by Edwin Hubble definitively showed that the Milky Way is just one of many galaxies.^[19]

The Milky Way is a barred spiral galaxy some 100,000–120,000 light-years in diameter which contains approximately 100–400 billionstars. It may contain at least as many planets as well.^[20][21] The Solar System is located within the disk, about 27,000 light-years away from the Galactic Center, on the inner edge of a spiral-shaped concentration of gas and dust called the Orion–Cygnus Arm. The stars in the inner ≈10,000 light-years form a bulge and one or more bars that radiate from the bulge. The very center is marked by an intense radio source named Sagittarius A* which is likely to be a supermassive black hole.

Stars and gases at a wide range of distances from the Galactic center orbit at approximately 220 kilometers per second. The constant rotation speed contradicts the laws of Keplerian dynamics and suggests that much of the mass of the Milky Way does not emit or absorbelectromagnetic radiation. This mass has been given the name "dark matter".^[22] The rotational period is about 240 million years at the position of the Sun.^[9] The Galaxy as a whole is moving at a velocity of approximately 600 km per second with respect to extragalactic frames of reference. The oldest known star in the Galaxy is at least 13.6 billion years old and thus must have formed shortly after the Big Bang.^[6] Surrounded by several smaller satellite galaxies, the Milky Way is part of the Local Group of galaxies, which forms a subcomponent of the Virgo Supercluster.The Milky Way is our home galaxy, containing our Solar System, where our planet, Earth, resides.^{[12][13][14][nb 1]} Its name "milky" is derived from its appearance as a dim glowing band arching across the night sky in which the naked eye cannot distinguish individual stars. The term "Milky Way" is a translation of the Classical Latin via lactea, from the Greek γαλαξίας κύκλος (pr. galaxías kýklos, "milky circle").^[15][16][17] From the Earth, the Milky Way appears like a band because its disk-shaped structure is viewed from within the Galaxy.Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. In the past, astronomers thought that all of the stars in the universe were contained inside of the Milky Way. Following the 1920 Great Debate between the astronomers Harlow Shapleyand Heber Curtis,^[18] observations by Edwin Hubble definitively showed that the Milky Way is just one of many galaxies.^[19]

The Milky Way is a barred spiral galaxy some 100,000–120,000 light-years in diameter which contains approximately 100–400 billionstars. It may contain at least as many planets as well.^[20][21] The Solar System is located within the disk, about 27,000 light-years away from the Galactic Center, on the inner edge of a spiral-shaped concentration of gas and dust called the Orion–Cygnus Arm. The stars in the inner ≈10,000 light-years form a bulge and one or more bars that radiate from the bulge. The very center is marked by an intense radio source named Sagittarius A* which is likely to be a supermassive black hole.

Stars and gases at a wide range of distances from the Galactic center orbit at approximately 220 kilometers per second. The constant rotation speed contradicts the laws of Keplerian dynamics and suggests that much of the mass of the Milky Way does not emit or absorbelectromagnetic radiation. This mass has been given the name "dark matter".^[22] The rotational period is about 240 million years at the position of the Sun.^[9] The Galaxy as a whole is moving at a velocity of approximately 600 km per second with respect to extragalactic frames of reference. The oldest known star in the Galaxy is at least 13.6 billion years old and thus must have formed shortly after the Big Bang.^[6] Surrounded by several smaller satellite galaxies, the Milky Way is part of the Local Group of galaxies, which forms a subcomponent of the Virgo Supercluster.http://en.wikipedia.org/wiki/Milky_Way

Andromeda Galaxy

The Andromeda Galaxy /ænˈdrɒmɨdə/ is a spiral galaxy approximately 2.5 million light-years (2.4×10¹⁹ km) from Earth^[4] in the Andromeda constellation. Also known as Messier 31, M31, or NGC 224, it is often referred to as the Great Andromeda Nebula in older texts. The Andromeda Galaxy is the nearest spiral galaxy to our Milky Way galaxy, but not the closest galaxy overall. It gets its name from the area of the sky in which it appears, the constellation of Andromeda, which was named after the mythological princess Andromeda. The Andromeda Galaxy is the largestgalaxy of the Local Group, which also contains the Milky Way, the Triangulum Galaxy, and about 30 other smaller galaxies. Although the largest, the Andromeda Galaxy may not be the most massive, as recent findings suggest that the Milky Way contains more dark matter and could be the most massive in the grouping.^[11] The 2006 observations by the Spitzer Space Telescope revealed that M31 contains one trillion (10¹²) stars:^[8] at least twice the number of stars in the Milky Way galaxy, which is estimated to be 200–400 billion.^[12]

The Andromeda Galaxy is estimated to be 7.1×10¹¹ solar masses.^[2] In comparison a 2009 study estimated that the Milky Way and M31 are about equal in mass,^[13] while a 2006 study put the mass of the Milky Way at ~80% of the mass of the Andromeda Galaxy. The two galaxies areexpected to collide in 3.75 billion years, eventually merging to form a giant elliptical galaxy.^[14]

At an apparent magnitude of 3.4, the Andromeda Galaxy is one of the brightest Messier objects,^[15] making it visible to the naked eye on moonless nights even when viewed from areas with moderate light pollution. Although it appears more than six times as wide as the full Moon when photographed through a larger telescope, only the brighter central region is visible to the naked eye or when viewed using binoculars or a small telescope.

http://en.wikipedia.org/wiki/Andromeda_Galaxyhttp://en.wikipedia.org/wiki/Andromeda_Galaxy

Galaksi Andromeda

Galaksi Andromeda dengan nama lain Messier 31, M31, atau NGC 224 adalah salah satu galaksi di luar galaksi Bima Sakti yang dapat dilihat dengan mata telanjang, asalkan dilihat pada malam yang cerah, tanpa bulan dan tanpa polusi cahaya. Strukturnya mirip dengan galaksi Bima Sakti yaitu berbentuk spiral. Jaraknya sekitar 2,5 juta tahun cahaya. Letaknya di langit adalah di belahan langit utara, sekitar 41 derajat di sebelah utara khatulistiwa langit, baik diamati sekitar bulan September, Oktober, November. Dengan mata telanjang, galaksi ini nampak seperti kabut tipis kecil di langit utara, tapi jika diamati dengan teropong yang dapat menampakkan bintang bintang redup di tepian galaksi Andromeda, ternyata ukuran Andromeda bisa lebih dari 7 kali diamter sudut bulan. Galaksi ini berisi sekitar 1 triliun bintang, dan bergerak mendekati Bima Sakti dengan kecepatan sekitar 300 km/detik.
http://id.wikipedia.org/wiki/Galaksi_Andromeda

Galaksi Terpadat Sejagat Raya

Ilmuwan menemukan galaksi yang padat layaknya kota Jakarta, berjarak 54 tahun cahaya dari Bumi, dinobatkan sebagai galaksi paling padat sejagat.

Dengan bantuan Hubble Space Telescope dan Chandra X Ray Observatory, ilmuwan menemukan bahwa galaksi bernama M60-UCD1 itu 15.000 kali lebih padat dibandingkan dengan Bimasakti.

"Berkelana dari bintang ke bintang akan lebih mudah di M60-UCD1 dibandingkan dengan di galaksi kita, tapi masih akan memakan waktu ratusan tahun dengan teknologi saat ini," kata Jay Strader dari Michigan State University yang memimpin studi.

Bagian paling padat dari galaksi tersebut adalah pusatnya, di mana 200 juta massa bintang tinggal dan terentang dalam radius hanya 80 tahun cahaya.

Hal itu berarti, jarak satu bintang dengan bintang lain di galaksi ini 25 kali lebih dekat dibandingkan dengan Bimasakti.

Chandra X Ray Observatory mengungkap bahwa pusat galaksi ini adalah sumber sinar X yang sangat kuat karena memiliki lubang hitam raksasa yang 10 juta kali lebih massif daripada Matahari. Ukuran lubang hitam itu dua kali lebih massif dari lubang hitam di Bimasakti.

Astronom memprediksi, di masa lalu, M60-USD1 berdekatan dengan galaksi lain dan bintang-bintangnya ditarik. Lubang hitam raksasa kemudian menarik bintang-bintang yang survive ke pusat.

"Kami berpikir hampir semua bintang telah ditarik dari bagian luar dari galaksi yang semula lebih besar dari saat ini," kata Duncan Forbes dari Swinburne University di Australia seperti dikutip National Geographic, Rabu (25/9/2013).

"Ini meninggalkan inti galaksi sebelumnya yang sangat padat dan lubang hitam supermassif," ungkapnya.
(Yunanto Wiji Utomo/Kompas.com)

source: national geographic