Hipotesis Planet

Planet, adalah benda astronomi yang mengorbit sebuah bintang atau sisa bintang yang cukup besar untuk memiliki grafitasi sendiri, tidak terlalu besar untuk menciptakan fusi termonuklir (sebuah proses saat dua inti atom bergabung dan membentuk inti atom yang lebih besar dan melepaskan energi).

dan telah "membersihkan" daerah orbitnya yang dipenuhi planetesimal (benda padat kecil yang mengelilingi suatu inti yang bersifat gas).

   Kata planet ini sendiri sudah lama ada dan memiliki hubungan sejarah, sains, mitologi, dan agama. Oleh peradaban kuno planet dipandang sebagai sesuatu yang abadi atau perwakilan dewa. Seiring kemajuan ilmu pengetahuan, pandangan manusia terhadap planet berubah. Pada tahun 2006, Persatuan Astronomi Internasional (IAU) mengesahkan sebuah resolusi resmi yang mendefinisikan planet di Tata Surya. Definisi ini dipuji tetapi juga dikritik san masih diperdebatkan oleh sejumlah ilmuan karena tidak mencakup benda - benda bermassa planet yang ditentukan oleh tempat atau benda orbitnya. Meski delapan benda planet yang ditemukan sebelum 1950 masih dianggap "planet" sesuai definisi modern, sejumlah benda angkasa seperti Ceres, Pallas, Juno, Vesta (masing - masing objek disabuk oleh asteroid Matahari), dan Pluto (objek trans-Neptunus yang pertama di temukan) yang dulunya dianggap planet oleh komunitas ilmuan sudah tidak dipermasalahkan lagi.

   

The Undersea World of Sound

Snorts, clicks,
whistles, groans
- tune in to the long-distance language of the ocean

The vast ocean of the world are dark, deep and mysterious place where eyesight counts for a little as soon as you venture very far beneath the surface.
   For humans, who lived in a world dominated by visual stimuli, to exits in such condition would be impossible. But for whales and dolphin that live in the ocean or in the case of a few species, muddy rivers and estuaries, the darkness is unimportant. what is crucial to them is sound.
   Sound is efficient way to transmit and sense information, especially as it travels five times faster trough water than trough air. if humans shout to someone, it is unlikely that they will be heard a kilometer away. But if a whale 'shouts' in an ocean channel, another whale may hear it tens, if not hundreds of kilometers away.
   Whale and dolphin use sound in two ways : communication and for echolocation. Dolphins, porpoises, and toothed whales communicate through a wide variety of high-frequency sounds - pure ton whistles, pulsed squeals, screams or barks - generally at frequencies of 500Hz to 20Hz (where hertz is a cycle per second and a kilohertz a thousand).
   But as well as using sound to communicate, toothed whales and dolphins also rely on echolocation to learn about their immediate environment, including prey that might be lurking nearby. They produce intense short broad-band pulses of sound in the ultrasonic range. of between 0.25 and 220 kHz. These clicks are brief - typically less than one millisecond long, but they are repeated many times each second.

Penguins show signs of stress

A new argument has been put forward as to whether penguins
are distributed by the presence of tourist in Antarctica.

Previous research by scientists from Keil University in Germany monitored Adelie penguins and noted that the birds' heart rated increased dramatically at the sight of a humans as far as 30 meters away. but new research using an artificial egg, which is equipped to measure heart rates, disputes this. Scientists from the Scott Polar Research Institute at Cambridge say that a slowing moving human who does not approach the nest too closely, is not perceived as a threat by penguins.
   The earlier findings have been used to partly explain the 20 per cent drop in populations of certain types of penguins near tourist sites. However, tour operations have continued to insist that their activities do not adversely affect wildlife in Antarctica, saying they encourage non-disruptive behaviour in tourists, an that the decline in penguin number is caused by other factors. 
   Amanda Nimon of the Scott Polar Research Institute spent three southern hemisphere summers at Cuverville Island in Antarctica studying penguin behaviour towards humans. "A nesting penguin will react very differently to a person rapidly and closely approaching the nest," says Nimon. "First they exhibit large and prolonged heart rate changes and then they often flee the nest leaving it open for predators to fly in and remove eggs or chicks." The artificial egg, specially developed for the project, monitored both the parent who had been 'disturbed' when the egg was placed in the nest and the other parent as they both took it in turns to guard the nest.
   However, Boris Culik, who monitored the Adelie penguins, believes that Nimon's findings do not invalidate his own research. He points out that species behave differently - and Nimon's work was with Gentoo penguin. Nimon and her colleagues believe that Culik's research was methodologically flawed because the monitoring of penguins' responses entailed capturing and restraining the birds and fitting them with heart - rate transmitters. therefore argues Nimon, it would not be surprising if they became stressed on seeing a human subsequently.