Saturn
土星 (13/6/2003)
也是時候拿張土星相來給大家看看。土星，似乎已成了天文的標誌，記得要畫一個行星的樣子時，很多時候都會畫一個有環的才像樣，很自然地，土星也代表了所有行星。但其實土星跟其他行星的樣子相似很遠，因為只有土星有一個那麼明顯的光環。你可以見到圖中還有一些它的衛星，另外，這張相的顏色不是真色，顏色的對比是誇大了的，其實是眾天文相中，大部份都是假色來的。
Caption::
This enhanced-color picture shows Saturn, its rings, and four of its icy
satellites. Three satellites (Tethys, Dione, and Rhea) are visible against
the darkness of space, and another smaller satellite (Mimas) is visible
against Saturn's cloud tops very near the left horizon and just below
the rings. The dark shadows of Mimas and Tethys are also visible on Saturn's
cloud tops, and the shadow of Saturn is seen across part of the rings.
Saturn, second in size only to Jupiter in our Solar System, is 120,660
km (75,000 mi) in diameter at its equator (the ring plane) but, because
of its rapid spin, Saturn is 10% smaller measured through its poles. Saturn's
rings are composed mostly of ice particles ranging from microscopic dust
to boulders in size. These particles orbit Saturn in a vast disk that
is a mere 100 meters (330 feet) or so thick. The rings' thinness contrasts
with their huge diameter--for instance 272,400 km (169,000 mi) for the
outer part of the bright A ring, the outermost ring visible here. The
pronounced concentric gap in the rings, the Cassini Division (named after
its discoverer), is a 3500-km wide region (2200 mi, almost the width of
the United States) that is much less populated with ring particles than
the brighter B and A rings to either side of the gap. The rings also show
some enigmatic radial structure ('spokes'), particularly at left. This
image was synthesized from images taken in Voyager's orange, blue, and
ultraviolet filters and was processed to create an exaggerated false color.
Credit::
NASA, JPL
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First
Stars 太初恆星 (12/6/2003)
跟天文有關的東西有很多，漂亮的也很多，相片固之然漂亮，但此外，一些畫家筆下的或電腦模擬出來的也不乏漂亮的。這張是電腦模擬出來，宇宙中最初誕生的第一批恆星會（這是其中一顆），當時週圍的氣體凝聚到中央形成恆星。為甚麼這麼強調這是太初恆星，宇宙中的第一批呢？因為宇宙一開始只有最輕的元素，例如氫和氦，但現在宇宙中有很多其他元素（要解釋就要用好長篇幅，簡單來說，就是元素之間在恆星的演變時做成的），這樣，形成的過程就不同了。由於我們不可能看到早期恆星怎樣演化，所以要借助電腦來模擬了。
Caption::
What became of the first stars? No known stars appear to be composed of
truly primordial gas -- all of the stars around us have too many heavy
elements. Our own Sun is thought to be a third generation star, with many
second-generation stars seen in globular clusters. This year, however,
significant progress is being made on solving this perennial astronomical
mystery. Analyses of recent WMAP satellite images of the cosmic microwave
background indicate that this primordial light was ionized by a first
generation of stars that came and went only 200 million years after the
Big Bang. Additionally computer codes are now more-accurately tracking
the likely creation and evolution of first stars in the early universe.
Pictured above at a scale of one light-month, a computer-generated model
resolves the scale of the first stars, indicating clean cocoons that condensed
into stars always over 30 times the mass of our Sun. Stars like this quickly
fused pristine gas into heavier elements and then exploded, seeding the
universe with elements that would become part of the stars we know and,
ultimately, ourselves.
Credit::
Ralf
Kaehler (ZIB), Tom Abel (Penn. State), Greg Bryan (Oxford) & Mike
Norman (UCSD)
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Io
and Jupiter 木星與木衛一伊奧 (11/6/2003)
木星是一個巨型的氣體行星，跟地球不一樣，除了核心外，它沒有實在的表面，它只是一團團的氣體。你可以清楚看到木星上雲頂的情形，位於正中很大的是木星的大紅斑，一個在木星上打了超過好幾百年的大颱風，這是一個木星很特別的標誌。左面橙色的一小粒，是木星的衛星伊奧，是我最喜歡的衛星，遲些再作介紹。有時會覺得行星的相比較起星雲星團等的相少了些變化，但原來它們的表面是很多變化的。值得一提的是，這張相是由前往土星途中的卡西尼號探測船路過木星時影的。
Caption::
The picture is a color composite, with enhanced contrast, taken from a
distance of 28.6 million kilometers (17.8 million miles). Jupiter's closest
large moon, Io, is visible at left. The edges of the Red Spot are cloudier
with ammonia haze than the spot's center is. The filamentary structure
in the center appears to spiral outward toward the edge. The Red Spot
region has changed in one notable way over the years: In images from NASA's
Voyager and Galileo spacecraft, the area surrounding the Red Spot is dark,
indicating relatively cloud-free conditions. Now, some bright white ammonia
clouds have filled in the clearings. This appears to be part of a general
brightening of Jupiter's cloud features during the past two decades. Jupiter
has four large moons and an array of tiny ones. In this picture, Io is
visible. The white and reddish colors on Io's surface are due to the presence
of different sulfurous materials while the black areas are due to silicate
rocks. Like the other large moons, Io always keeps the same hemisphere
facing Jupiter, called the sub-Jupiter hemisphere. The opposite side,
much of which we see here, is the anti-Jupiter hemisphere. Io has more
than 100 active volcanoes spewing very hot lava and giant plumes of gas
and dust. Its biggest plume, Pele, is near the bottom left edge of Io's
disk as seen here.
Credit::
NASA/JPL/University
of Arizona
|
Emperor
Penguins II 皇帝企鵝 II (10/6/2003)
皇帝企鵝是生活於南極洲的動物，牠們是一夫一妻制的，非常專一。牠們每年最多只會生一隻小企鵝，因為在南極那麼惡劣的天氣下，要同時撫養幾隻企鵝，是根本無可能的。皇帝企鵝跟其他的企鵝很不同，牠們居住於南極洲的內陸，而非近海的地方。當企鵝媽媽生完蛋後，就會交由爸爸照顧，然後就由南極洲內陸走到80公里外的海岸覓食，這樣一來一回，就要超過二個月時間，當媽媽回來，就把食物吐出來餵其伴侶與出世的孩子，之後就到爸爸外出，媽媽照顧小企鵝。看見牠們這樣去撫養小企鵝，真是覺得很辛苦。圖中的企鵝們正覓食完回家，牠們正在橫渡結了冰的威爾德海，那是南極洲最大的海。
Caption::
Emperor Penguins are creatures living on Antarctica. Under the extreme
weather of Antarctica, the female penguin only lays one egg and then leaves.
The male take the responsibility of keeping the egg cosy. The female head
for the open sea 80km away for feeding. This takes more than 2 months
for them completing this journey. After the mother returns, the father
goes out for feed again. This picture showing the penguins are returning
to their colony across the sea ice of the Weddell Sea, the largest sea
of Antarctica.
Credit::
David
Tipling
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Startrails
星流跡 (9/6/2003)
當星在天上留下痕跡，那就是星流跡。星星跟太陽月亮一樣會升會落，會移動位置，這全因為地球會轉動，若你用相機（注意，數碼相機做不到這個效果的）長期曝光，恆星在天上走過的路徑就會被你拍下來，成為了這些的星流跡。所以相中每條線都是一顆星在天上經過的地方，這些星流跡的相是最易影的天文相，效果也是不錯的。你會發現所有星都是圍著同一個地方來轉，那正是天上的北極，北極星正位於那裏（其實差少少，不是那麼正），就是因為北極星在天上的位置不會改變，古人就利用了它來辦認方向了。星流跡相，是要有一個好的背景襯托才靚的，這張相就是由海拔2000米的雲頂所攝的。
Caption::
Like the sun and moon, stars rotate in the sky, the path they travelled
are called startrails. When you use an camera, but not a digitial one,
you can photograph startrails by using long exposure. You can see that
all the stars are all rotating around a fixed point - the celestial pole.
Our polaris is located there, as it is always state there, people were
using it for navigation long time ago. For a good picture of startrails,
a good background is critical, and this one, got a background of sea of
clounds over 2000m of altitude.
Credit::
J.C.
Casado
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