You are here: Home / Archives for omni-directional dipole antennas
The Sky is Waiting.
Search AstroGuyz
Custom Search
Advertise on Astroguyz!
|
|
|
 |
|
Pictured is a Delta IV rocket launch from Cape Canaveral on November 21st, 2010. The image is a 20 second exposure taken at dusk, shot from about 100 miles west of the launch site. The launch placed a classified payload in orbit for the United States Air Force.
Difficult but not impossible to catch against the dawn or dusk sky, spotting an extreme crescent moon can be a challenge. The slender crescent pictured was shot 30 minutes before sunrise when the Moon was less than 20 hours away from New. A true feat of visual athletics to catch, a good pair of binoculars or a well aimed wide field telescopic view can help with the hunt.
The Sun is our nearest star, and goes through an 11-year cycle of activity. This image was taken via a properly filtered telescope, and shows the Sun as it appeared during its last maximum peak in 2003. This was during solar cycle #23, a period during which the Sun hurled several large flares Earthward. The next solar cycle is due to peak around 2013-14.
Located in the belt of the constellation Orion, Messier 42, also known as the Orion Nebula is one of the finest deep sky objects in the northern hemisphere sky. Just visible as a faint smudge to the naked eye on a clear dark night, the Orion Nebula is a sure star party favorite, as it shows tendrils of gas contrasted with bright stars. M42 is a large stellar nursery, a star forming region about 1,000 light years distant.
Orbiting the planet in Low Earth Orbit (LEO) every 90 minutes, many people fail to realize that you can see the International Space Station (ISS) from most of the planet on a near-weekly basis. In fact, the ISS has been known to make up to four visible passes over the same location in one night. The image pictured is from the Fourth of July, 2011 and is a 20 second exposure of a bright ISS pass.
Next to the Sun, the two brightest objects in the sky are the Moon and the planet Venus. In fact, when Venus is favorably placed next to the Moon, it might just be possible to spot the two in the daytime. Another intriguing effect known as earthshine or ashen light is also seen in the image on the night side of the Moon; this is caused by sunlight reflected back off of the Earth towards our only satellite.
A mosaic of three images taken during the total lunar eclipse of December 21st, 2010. The eclipse occurred the same day as the winter solstice. The curve and size of the Earth’s shadow is apparent in the image.
02.11.09:The Low-Down on LOFAR.
European radio astronomers at the Netherlands Institute for Radio Astronomy (ASTRON) have recently opened a potentially new window on the universe with an exotic new instrument. Dubbed LOFAR, or the Low Frequency Array, this unique instrument will examine the sky at extremely low radio frequencies, with a low band of 30 to 78 MHz and a complimenting high band of 120 to 168 MHz. In contrast, the radio dish at the Arecibo Observatory in Puerto Rico operates in a range of 400-5000 MHz. We’re talking very low frequencies, in a range not well understood. Three arrays currently centered on Exloo in the Netherlands saw first “radio light” earlier this year, examining the powerful radio source Cygnus A, a suspected black hole candidate. As computer power increases, scientists hope to add arrays across Europe from Britain to the Ukraine to increase the resolution of the array. The low gain antenna masts are simple and cheap to construct, and are basic omni-directional dipole antennas utilizing a synthetic aperture. LOFAR will map events at low radio frequencies, from ionization in the Earth’s atmosphere caused by gamma-ray bursts to corneal mass ejections on the Sun to re-ionization of neutral hydrogen in the primordial universe. And that’s not to mention any surreptitious discoveries that always seem to crop up when a new portion of the electromagnetic spectrum gets analyzed… perhaps some ultra-advanced race communicates via low frequency black hole resonances? I seem to remember a plot in Arthur C. Clarke’s Imperial Earth that involved intelligent aliens and low frequency waves… watch for LOFAR “antenna farms” cropping up along the European country-side soon!