The Big Dipper and the Lyrids
Thursday, April 22 2010 @ 01:10 pm EDT
Contributed by: dgrosvold
This time of year, the Big Dipper rides high in the northeastern sky in the evenings, tilted back so the “water” runs out and appears to fill the bowl of the Little Dipper. The Big Dipper and Little Dipper are asterisms found in the constellations of Ursa Major, the Great Bear, and Ursa Minor, the Lesser Bear, respectively. An asterism is a highly recognizable pattern in the night sky that is not one of the 88 constellations designated by the International Astronomical Union (IAU). Although the pattern may wholly reside in a single constellation, often times it does not. An asterism may even be what we recognize as a constellation, as is the case with the Big Dipper, which is what we normally think of when we look for the constellation Ursa Major. As mentioned in a previous column, the “pouring out” of the Big Dipper is typically associated with the coming of spring rains.
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Although the Lyrids are common throughout the month of April, this week is the best time to view this meteor shower. Astronomers expect this lesser-known shower to be active Thursday and Friday morning in the hour or so before dawn, just after the Moon sets. The Lyrids are typically weak, but are known for occasional outbursts and sometimes even large bolides (fireballs,) like the one that occurred in the northern sky on April 10th.
The April 10th fireball was visible from Fort Smith and all over NW Arkansas. All of the meteors in this shower appear to come from somewhere in the constellation Lyra, which is home to the bright star Vega. Vega was popularized as the source of alien signals in the 1997 movie Contact, based on Carl Saganís book by the same name.
The latter half of this week will also be a great time to observe the Moon, which passed First Quarter at 1:20 PM CDT on Wednesday April 21st. Using a small telescope or binoculars reveals a myriad of craters and other lunar features. Pay special attention to the terminator, which is the line of demarcation between the lit portion of the Moon and the dark side. Here, you will find the best contrast which in turn enables you to see the smallest details.
On Thursday evening, April 22nd, the Moon will be in a very nice tight grouping with Mars, the Beehive Cluster (also known as Praesepe or M44,) the bright asteroid Vesta, and Regulus. Regulus is the bright star at the end of the handle in the Sickle of Leo, another well-known asterism. Look below the Moon on Thursday evening for the orange-red star Alphard, the heart of Hydra, the Water Snake.
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On Friday evening, April 23rd, Venus and the Pleiades (pronounced PLEE-a-deez, also known as the Seven Sisters or M45,) will be within the 5° of a single field of view in binoculars. Look for them low in the west just after sunset.
The International Space Station (ISS) will pass overhead several times over the next few days, but the two brightest passes will be on Monday and Tuesday mornings at 5:33 AM and 5:57 AM, respectively. In both cases, the ISS will begin rising in the NW. On Monday, April 26th the ISS will reach maximum altitude of 67° in the NE, at a magnitude of -3.0. On Tuesday, April 27th, it will only reach 27° in the SW at a magnitude of -2.3. You can find out more detail about when the ISS will be overhead at http://www.heavens-above.com.