April 4: Moon and Planets
We can’t go back in time to see what the planets were like in
the distant past. But scientists can still tell us a lot about the
histories of these worlds. They look at many clues, including their
magnetic fields.
By the University of Texas McDonald Observatory
April 4: Moon and Planets
We can’t go back in time to see what the planets were like in the distant past. But scientists can still tell us a lot about the histories of these worlds. They look at many clues, including their magnetic fields.
For example, scientists are learning that giant continental plates may once have floated atop the crust of Mars – plates like those found on Earth today.
Look for Mars not far from the Moon tonight. It’s to the west of the Moon at nightfall, and looks like a bright orange star. The even brighter planet Saturn is about the same distance to the east of the Moon, and shines with a golden hue.
April 5: Moon and Saturn
Seen through a telescope, the rings of Saturn look flat and unchanging. In reality, though, Saturn’s rings are a diverse and dynamic system that’s fed and herded by small moons.
Saturn follows our own Moon across the sky tonight. It’s to the east of the Moon, and follows it down the western sky in late evening. It looks like a bright golden star. Saturn’s rings are visible through even the most modest of telescopes.
One of Saturn’s larger moons, Enceladus, appears to “feed” one of the outer rings. Fountains of ice spew into space from near its south pole, providing fresh ice for Saturn’s dynamic rings.
April 6: Listening Post
If alien civilizations are beaming messages to the rest of the galaxy, a new listening post in California is ready to hear them. It’s scheduled to start operations this month.
The listening post is called the Allen Telescope Array, after its benefactor, Paul Allen. Right now, it consists of 42 fairly small radio telescopes. A sophisticated computer system will combine their signals, so they’ll have the same sensitivity as a single radio dish spanning half the length of a football field.
April 7: Arrival at Venus
We sometimes complain about weather that never seems to change. In northern climes, it’s the never-ending winter. In the south, it’s unrelenting summer. For weather that really never changes, though, look at the planet Venus. Temperatures are always more than 850 degrees Fahrenheit, there’s never much wind at the surface, and the sky is always cloudy – but it never rains.
Scientists hope to learn a lot more about Venus’s weather from a spacecraft that’s scheduled to enter orbit around the planet next week. It’s called Venus Express. It was built by the European Space Agency, using spare parts from a Mars mission.
Venus Express is scheduled to operate for two Venus days. That may not sound like much, until you consider that each day is about eight months long.
April 8: Moon and Regulus
The system that astrononomers use to classify stars sounds like a game of Bingo. Consider Regulus, the brightest star in Leo, the lion, which snuggles very close to the Moon tonight. Regulus is a B7 star – a designation that reveals its color and surface temperature.
Astronomers describe most stars with the letters O, B, A, F, G, K, and M. Class “O” stars are the hottest, with surface temperatures upwards of 60,000 degrees Fahrenheit and a distinctly blue color. “M” stars are the coolest, and they look orange or red. The Sun is a “G” star, with a surface temperature around 10,000 degrees and a slightly yellow color.
But the letters are only a rough designation – there’s a wide temperature range within each one. To be a little more precise, astronomers add a number after the letter, from zero to nine. And to narrow things down even more, they add a Roman numeral after that – from one to five. The Roman “one” indicates that a star is a supergiant, while a “five” shows that it’s a “main-sequence” star – a star in the prime of life, like the Sun.
Regulus, at B-7-5, is also a main-sequence star, but it’s a good bit hotter and whiter than the Sun.
Look for B7 on your Bingo cards, and B7 Regulus just a whisker away from the Moon tonight.
April 9: Lunar Landscape
As the gibbous Moon climbs overhead tonight, look at the light and dark features on its mottled surface – mountains and plains that formed long ago. Other than our own Earth, the Moon is the only body in the universe whose features are easily visible to the unaided eye.
The dark features are called “seas,” because people used to think they were filled with water. Instead, they’re vast plains of volcanic rock.
Watch the Moon as it climbs high across the sky during the night. It’s already high in the sky at nightfall, with the bright star Regulus – the “heart” of Leo, the lion – close by. Regulus leads the Moon across the sky.
April 10: Lightning
No horror movie is complete without a few lightning bolts to light up the night sky – and apparently, neither is any planet with a thick, turbulent atmosphere.
Lightning is a massive electrical spark. On Earth, it forms inside towering clouds with powerful updrafts and downdrafts. The motions of water droplets and ice crystals in the cloud build up an electric charge, which DIScharges as a bolt of lightning.
Typically, about a hundred lightning flashes occur on Earth every second. We see more than our fair share in the United States at this time of year as storm season cranks up.
