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Astronomy Picture Of the Day (APOD)
A Martian Autumn Begins
23.09.1997
Today is the first day of Autumn in the Northern Hemisphere of Planet Earth. The Autumnal Equinox occured yesterday at 7:56 pm EDT as the Sun crossed the celestial equator from North to South.
Antares and Rho Ophiuchi
22.09.1997
Why is the sky near Antares and Rho Ophiuchi so colorful? The colors result from a mixture of objects and processes. Fine dust illuminated from the front by starlight produces blue reflection nebulae. Gaseous clouds whose atoms are excited by ultraviolet starlight produce reddish emission nebulae. Backlit dust clouds block starlight and so appear dark.
Looking Down on Saturn
21.09.1997
This picture of Saturn could not have been taken from Earth. No Earth based picture could possibly view the night side of Saturn and the corresponding shadow cast across Saturn's rings. Since Earth is much closer to the Sun than Saturn, only the day side of the planet is visible from the Earth.
The Clouds of Jupiter
20.09.1997
What makes the colors in Jupiter's clouds? With a mean temperature of 120 degrees Kelvin (-153 degrees Celsius) and a composition dominated by hydrogen (about 90%), and helium (about 10%) with a smattering...
Globular Cluster 47 Tucanae
19.09.1997
Stars come in bunches. Of the over 200 globular star clusters that orbit the center of our Milky Way Galaxy, 47 Tucanae is the second brightest globular cluster (behind Omega Centauri). Known to some affectionately as 47 Tuc or NGC 104, it is only visible from the Southern Hemisphere.
Erupting Sun
18.09.1997
On August 27th twisting magnetic fields propelled this huge eruptive prominence a hundred thousand miles above the Sun's surface. The seething plasma of ionized gases is at a temperature of about 150,000 degrees Farenheit and spans over 200,000 miles (about 27 Earths).
GRB Fireball Persists
17.09.1997
It's still there. The optical counterpart to the instantly famous gamma-ray burst (GRB) that occurred last February 28th has faded - but not completely. The astronomical community had waited patiently for months...
Moon Over Mongolia
16.09.1997
Fighting clouds and the glow of city lights, a young Moon shines over the western horizon of Mongolia's capital Ulaan-Baatar. The thin sunlit crescent is 1.5 days old and strongly over exposed in this image taken on March 10.
Olympus Mons on Mars: The Largest Volcano
15.09.1997
The largest volcano in the Solar System is on Mars. Olympus Mons rises 24 kilometers high and measures 550 km across. By comparison, Earth's largest volcano, Mauna Loa in Hawaii, rises 9 km high and measures 120 km across.
MyCn18: An Hourglass Nebula
14.09.1997
The sands of time are running out for the central star of this hourglass-shaped planetary nebula. With its nuclear fuel exhausted, this brief, spectacular, closing phase of a Sun-like star's life occurs as its outer layers are ejected - its core becoming a cooling, fading white dwarf.
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