The Summer Triangle
On July evenings, look eastward in the evening for the season’s signature star pattern. It’s an asterism called the Summer Triangle, and, as you might guess, it consists of three stars: blue-white Vega, distant Deneb and fast-spinning Altair.
They’re the first three stars to light up the eastern half of the sky after sunset. You can see them even from light-polluted cities, or on a moonlit night.
Watch for the Summer Triangle pattern in the evening beginning around June, through the end of each year.
Vega is bright and blue-white
Blue-white Vega shines brightest of the three stars in the Summer Triangle. It’s the brightest star in the east in the evening on July evenings. And it’s the brightest light in the constellation Lyra the Harp. Thus Vega is also known as Alpha Lyrae. It shines at magnitude +0.03.
Vega is located about 25 light-years away from us. Many people recognize Vega’s constellation, Lyra. This pattern of stars looks like a triangle of stars connected to a parallelogram.
Skywatchers around the world have a special place in their hearts for the beautiful blue-white star, Vega. Come to know it, and you will see why.
How to see Vega and its constellation
Observers in the Northern Hemisphere typically begin noticing Vega in the evening around May, when this star comes into view in the northeast in mid-evening. Throughout northern summer, Vega shines brightly in the east in the evening. It’s high overhead on northern autumn evenings, and in the northwest by December evenings.
The little constellation Lyra has some interesting features. Near Vega you can see Epsilon Lyrae, which telescope users know as a famous double-double star. In other words, through small telescopes, you can see Epsilon Lyrae as double, with each of the two components also a double star.
Meanwhile, another famous telescopic sight lies between the Gamma and Beta stars in Lyra, the Ring Nebula, also called M57.
You can see Vega, Epsilon Lyrae and M57 (the Ring Nebula) marked on the chart below.
Science of the star Vega
Vega is the fifth-brightest star visible from Earth, and the third-brightest easily visible from mid-northern latitudes, after Sirius and Arcturus. At about 25 light-years away, it is the sixth-closest of all the bright stars, or fifth if you exclude Alpha Centauri, which most of the Northern Hemisphere can’t easily see.
The star’s distinct blue color indicates a surface temperature of nearly 17,000 degrees Fahrenheit (9,400 Celsius), which is is about 7,000 degrees F (4,000 C) hotter than our sun. Vega’s diameter is roughly 2.5 times the diameter of the sun, and it has about twice its mass. But Vega’s internal pressures and temperatures, far greater than our sun’s, will cause it to burn its internal fuel faster. At only half a billion years old, Vega is already middle-aged. That’s in contrast to our middle-aged sun, which is 4 1/2 billion years old. Vega is only about a tenth our sun’s age, but it will run out of fuel in only another half-billion years.
In astronomer-speak, Vega is an “A0V main sequence star.” The “A0” signifies its temperature, whereas the “V” is a measure of energy output (luminosity), indicating that Vega is a normal star (not a giant). “Main sequence” means it’s in the category of normal stars, and produces energy through stable fusion of hydrogen into helium. With a visual magnitude of +0.03 (apparent brightness), Vega appears only marginally dimmer than Arcturus, but with a distinctly different, cool-blue color.
Vega rotates so fast it’s flattened
Vega rotates rapidly, making a single full rotation about its axis once about every 12.5 hours. In contrast, our sun requires 27 days to spin once. As a result, if you could visit Vega in space, you’d find it noticeably flattened, as shown in the computer simulation below. Though a fast spinner, Vega isn’t the fastest of the three Summer Triangle stars. Altair rotates once in only about 10 hours!
Vega appears to have an asteroid belt
In 2018, astronomers announced it appears Vega has a large asteroid belt surrounding it. NASA’s Spitzer Space Telescope and the European Space Agency’s Herschel Space Observatory detected a ring of warm, rocky debris. NASA said:
In this diagram, the Vega system, which was already known to have a cooler outer belt of comets (orange), is compared to our solar system with its asteroid and Kuiper belts. The relative size of our solar system compared to Vega is illustrated by the small drawing in the middle. On the right, our solar system is scaled up four times.
The comparison illustrates that both systems have inner and outer belts with similar proportions. The gap between the inner and outer debris belts in both systems works out to a ratio of about 1-to-10, with the outer belt 10 times farther away from its host star than the inner belt.
Astronomers think that the gap in the Vega system might contain planets, as is the case in our solar system.
In tradition and myth
In western skylore, Vega’s constellation Lyra was a harp played by the legendary Greek musician Orpheus. According to legend, when Orpheus played his harp, neither god nor mortal could turn away.
In western culture, Vega is known as the Harp Star.
But Asia has the most beautiful stories relating to Vega. In China, the legend speaks of a forbidden romance between the goddess Zhinü – represented by Vega – and a humble farm boy, Niulang, represented by the star Altair. Separated in the night sky by the Milky Way, or Celestial River, the two lovers may meet only once a year. It’s said that their meeting comes on the 7th night of the 7th moon, when a bridge of magpies forms across the Celestial River, and the two lovers briefly reunite.
Their reunion marks the time of the Qixi Festival.
More star lore
In Japan, the Tanabata festival features Orihime, a celestial princess or goddess, represented by Vega, who falls in love with a mortal, Hikoboshi, represented by the star Altair. However, this enrages Orihime’s father so he forbids her to see this mere mortal. Then … you know the story. The gods place the two lovers in the sky, separated by the Celestial River or Milky Way. Yet the sky gods in kindness let them reunite on the 7th night of the 7th moon each year. Sometimes Hikoboshi’s annual trip across the Celestial River is treacherous, though, and he doesn’t make it. In that case, Orihime’s tears form raindrops that fall over Japan.
Many Japanese celebrations of Tanabata occur in July, but sometimes they take place in August. Sometimes the Perseid meteor shower represents Orihime’s tears in myth.
For observation, Vega’s position is RA: 18h 36m 56.3s, dec: +38° 47′ 1.3″.
Bottom line: The star Vega in the constellation Lyra is one of the sky’s most beloved stars, for people around the world.
Our Summer Triangle series includes:
Deneb is distant and very luminous
The post Summer Triangle star: Vega is bright and blue-white first appeared on EarthSky.
from EarthSky https://ift.tt/ohPE6qR
The Summer Triangle
On July evenings, look eastward in the evening for the season’s signature star pattern. It’s an asterism called the Summer Triangle, and, as you might guess, it consists of three stars: blue-white Vega, distant Deneb and fast-spinning Altair.
They’re the first three stars to light up the eastern half of the sky after sunset. You can see them even from light-polluted cities, or on a moonlit night.
Watch for the Summer Triangle pattern in the evening beginning around June, through the end of each year.
Vega is bright and blue-white
Blue-white Vega shines brightest of the three stars in the Summer Triangle. It’s the brightest star in the east in the evening on July evenings. And it’s the brightest light in the constellation Lyra the Harp. Thus Vega is also known as Alpha Lyrae. It shines at magnitude +0.03.
Vega is located about 25 light-years away from us. Many people recognize Vega’s constellation, Lyra. This pattern of stars looks like a triangle of stars connected to a parallelogram.
Skywatchers around the world have a special place in their hearts for the beautiful blue-white star, Vega. Come to know it, and you will see why.
How to see Vega and its constellation
Observers in the Northern Hemisphere typically begin noticing Vega in the evening around May, when this star comes into view in the northeast in mid-evening. Throughout northern summer, Vega shines brightly in the east in the evening. It’s high overhead on northern autumn evenings, and in the northwest by December evenings.
The little constellation Lyra has some interesting features. Near Vega you can see Epsilon Lyrae, which telescope users know as a famous double-double star. In other words, through small telescopes, you can see Epsilon Lyrae as double, with each of the two components also a double star.
Meanwhile, another famous telescopic sight lies between the Gamma and Beta stars in Lyra, the Ring Nebula, also called M57.
You can see Vega, Epsilon Lyrae and M57 (the Ring Nebula) marked on the chart below.
Science of the star Vega
Vega is the fifth-brightest star visible from Earth, and the third-brightest easily visible from mid-northern latitudes, after Sirius and Arcturus. At about 25 light-years away, it is the sixth-closest of all the bright stars, or fifth if you exclude Alpha Centauri, which most of the Northern Hemisphere can’t easily see.
The star’s distinct blue color indicates a surface temperature of nearly 17,000 degrees Fahrenheit (9,400 Celsius), which is is about 7,000 degrees F (4,000 C) hotter than our sun. Vega’s diameter is roughly 2.5 times the diameter of the sun, and it has about twice its mass. But Vega’s internal pressures and temperatures, far greater than our sun’s, will cause it to burn its internal fuel faster. At only half a billion years old, Vega is already middle-aged. That’s in contrast to our middle-aged sun, which is 4 1/2 billion years old. Vega is only about a tenth our sun’s age, but it will run out of fuel in only another half-billion years.
In astronomer-speak, Vega is an “A0V main sequence star.” The “A0” signifies its temperature, whereas the “V” is a measure of energy output (luminosity), indicating that Vega is a normal star (not a giant). “Main sequence” means it’s in the category of normal stars, and produces energy through stable fusion of hydrogen into helium. With a visual magnitude of +0.03 (apparent brightness), Vega appears only marginally dimmer than Arcturus, but with a distinctly different, cool-blue color.
Vega rotates so fast it’s flattened
Vega rotates rapidly, making a single full rotation about its axis once about every 12.5 hours. In contrast, our sun requires 27 days to spin once. As a result, if you could visit Vega in space, you’d find it noticeably flattened, as shown in the computer simulation below. Though a fast spinner, Vega isn’t the fastest of the three Summer Triangle stars. Altair rotates once in only about 10 hours!
Vega appears to have an asteroid belt
In 2018, astronomers announced it appears Vega has a large asteroid belt surrounding it. NASA’s Spitzer Space Telescope and the European Space Agency’s Herschel Space Observatory detected a ring of warm, rocky debris. NASA said:
In this diagram, the Vega system, which was already known to have a cooler outer belt of comets (orange), is compared to our solar system with its asteroid and Kuiper belts. The relative size of our solar system compared to Vega is illustrated by the small drawing in the middle. On the right, our solar system is scaled up four times.
The comparison illustrates that both systems have inner and outer belts with similar proportions. The gap between the inner and outer debris belts in both systems works out to a ratio of about 1-to-10, with the outer belt 10 times farther away from its host star than the inner belt.
Astronomers think that the gap in the Vega system might contain planets, as is the case in our solar system.
In tradition and myth
In western skylore, Vega’s constellation Lyra was a harp played by the legendary Greek musician Orpheus. According to legend, when Orpheus played his harp, neither god nor mortal could turn away.
In western culture, Vega is known as the Harp Star.
But Asia has the most beautiful stories relating to Vega. In China, the legend speaks of a forbidden romance between the goddess Zhinü – represented by Vega – and a humble farm boy, Niulang, represented by the star Altair. Separated in the night sky by the Milky Way, or Celestial River, the two lovers may meet only once a year. It’s said that their meeting comes on the 7th night of the 7th moon, when a bridge of magpies forms across the Celestial River, and the two lovers briefly reunite.
Their reunion marks the time of the Qixi Festival.
More star lore
In Japan, the Tanabata festival features Orihime, a celestial princess or goddess, represented by Vega, who falls in love with a mortal, Hikoboshi, represented by the star Altair. However, this enrages Orihime’s father so he forbids her to see this mere mortal. Then … you know the story. The gods place the two lovers in the sky, separated by the Celestial River or Milky Way. Yet the sky gods in kindness let them reunite on the 7th night of the 7th moon each year. Sometimes Hikoboshi’s annual trip across the Celestial River is treacherous, though, and he doesn’t make it. In that case, Orihime’s tears form raindrops that fall over Japan.
Many Japanese celebrations of Tanabata occur in July, but sometimes they take place in August. Sometimes the Perseid meteor shower represents Orihime’s tears in myth.
For observation, Vega’s position is RA: 18h 36m 56.3s, dec: +38° 47′ 1.3″.
Bottom line: The star Vega in the constellation Lyra is one of the sky’s most beloved stars, for people around the world.
Our Summer Triangle series includes:
Deneb is distant and very luminous
The post Summer Triangle star: Vega is bright and blue-white first appeared on EarthSky.
from EarthSky https://ift.tt/ohPE6qR
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