Boötes, representing a “herdsman” or “ploughman”, is a distinctly kite-shaped constellation that can be seen in the night sky by observers located between +90° and -50° of latitude. It is the 13th biggest constellation in the night sky, taking up an area of 907 square degrees of the northern celestial hemisphere, and also contains the third most luminous star in the entire sky, the red supergiant star Arcturus. Boötes is also home to five stars with confirmed planets, but contains no Messier objects.
Ursa Major Family of Constellations
Boötes belongs to the Ursa Major family of constellations, together with Camelopardalis, Canes Venatici, Coma Berenices, Corona Borealis, Draco, Leo Minor, Lynx, Ursa Major, and Ursa Minor,
There are several myths associated with the constellation Boötes, with perhaps the most famous story associating it with Icarius, a grape grower who invited the god Dionysus to inspect his vineyards. Dionysus was duly impressed by what he saw, and as a reward, he taught the Athenian viticulturist the secret of wine-making. Icarius turned out to be a star pupil, and produced such good wines that he decided to invite all his friends to come and sample the fruits of his work. His shepherd friends, however, had no idea what they were drinking, and the next day after suffering from the world’s first hangovers, subsequently accused him of trying to poison them, and killed him in revenge. Icarius’s daughter Erigone and her faithful hound Maera also killed themselves after learning of his murder. Dionysus was said to be so saddened by the killing of his friend that he placed him in the sky as a sign of his affection, where he can still be seen to this day as the constellation Boötes. Erigone and Maera, too, were placed in the heavens as the constellations Virgo and Canis Minor.
– Arcturus (Alpha Boötis), a red giant (K1.5 IIIpe) located about 37 light years away, is the night sky’s 4th most luminous star with an apparent magnitude of -0.04. It is around 25 times bigger than our sun, 1.5 times more massive, and at least 110 times more luminous. Arcturus is ancient Greek for the “guardian of the bear”, with the star found by the Herdsman’s left foot. The star’s location on the celestial equator also makes it easy to spot from both hemispheres, and from northern locations can be found by following the arc of the Big Dipper’s handle away from asterism’s “bowl”. Arcturus is believed to a member of the 52-strong Arcturus Stream, a small group of stars that is moving perpendicularly through the plane of the Milky Way. It is also a member of the Local Fluff, or more precisely, the Local Interstellar Cloud, a 30-light-year-diameter interstellar cloud through which the entire solar system is currently moving.
– Izar (Epsilon Boötis), the second brightest star in Boötes, is a binary star found 300 light years from our solar system with a visual magnitude of 2.37. Its primary component is an orange giant, while its smaller companion is a faint blue-green colored star.
– Nekkar (Beta Boötis) is a yellow giant (G8 IIIa) star located about 220 light years away from Earth. What makes it remarkable is the fact that it is a variable star of the flare type, meaning it can brighten dramatically in the space of just a few minutes. It is at around 250 million years old, at least 21 times bigger than the Sun, and anything between 170 and 195 times as luminous, depending on its state of variability at any given time.
– Seginus (Gamma Boötis) is located about 85 light years away, and is classified as a Delta Scuti variable star with an A7III classification. Delta Scuti variable stars show only marginal variations in brightness, and in the case of Seginus, its magnitude variations of between 3.02 and 3.07 are the result of both rotational and non-rotational pulsations that occur on its surface with a period of only 6.79 hours.
Other stars of interest in Boötes includes the white dwarf Lambda Boötis; the blue-White subgiants Asellus Primus, Asellus Tertius, and Merga; the yellow-white dwarf Sigma Boötis; and the orange giants Rho Boötis, Upsilon Boötis, and Nadlat.
Notable Deep Sky Objects
Boötes may not contain any Messier objects, but it does have a number of interesting deep-sky targets for astronomers.
– The Boötes Void is a hole in the Universe that has been described as the “spookiest place ever” with good reason. Consider this; our cosmic backyard is populated by more than 30 galaxies, collectively known as the Local Group, spanning an area of around 10 million light years. The Boötes Void, however, spans an area of around 300 million light years – and it contains only 60 known galaxies in a volume of space that represents 0.27% of the diameter of the known Universe.
This is the largest void yet discovered, and its volume of about 230,000 cubic mega-parsecs should have contained around 10,000 galaxies. To put this volume into some kind of perspective is almost impossible, so let’s replace the average density of galaxies with a simple graph that represents galactic density as valleys and peaks. On such a graph, galaxies would show as the peaks of narrow, steeply tapering “towers”. For instance, typical galaxies such as the Milky Way would be represented as a peak with about the same footprint and height as the Empire State Building, while even a modestly sized void would represent a three-foot-deep hole that is three times as big as Manhattan. On this scale, the Boötes Void would swallow most of the U.S. Eastern Seaboard.
Another way of describing this hole in the Universe would be to say, as American astronomer Gregory Scott Alderling once did “….if the Milky Way had been in the centre of the Boötes Void, we wouldn’t have known there were other galaxies until the 1960s.”
Scientists have no explanation for how such a hole could have formed, apart from positing that this Void is the result of several smaller voids coalescing; however, cosmological models suggest that the Universe is not old enough for natural processes to have emptied out such a large volume. Regardless of how the Void came to be, the galaxies in it are on average more luminous than galaxies outside of it, but what is really strange is that the galaxies in the hole are arranged in the shape of a tube, a phenomenon that occurs nowhere else, and which has so far resisted a rational explanation.
– Boötes I (Boötes Dwarf Galaxy) is a diminutive galaxy just 720 light years across that is located about 197,000 light years from Earth. With an apparent magnitude of 13.1, it is one of the faintest known galaxies, and its distorted shape is believed to be the result of the Milky Way’s tidal gravity pulling it apart.
Other objects on interest in Boötes includes NGC 5466, a globular star cluster consisting of thousands of stars; as well as several galaxies including NGC 5248, NGC 5676, NGC 5008, NGC 5886, NGC 5888, and NGC 5698.
There are three main meteor showers associated with the constellation Boötes, namely the January Boötids, the June Boötids, and the Quadrantids.
– January Boötids can peak at any time between January 9th and 18th, with its highest hourly rate ever recorded occurring in 1957 when just 25 meteors per hour were seen. However, this meteor shower is not known for its spectacular displays, nor does it occur every year.
– June Boötids, another weak shower, runs from June 26th and July 2nd with a peak on the 28th when a mere one or two meteors per hour may be seen. However, there have been more productive outbursts, most notably the shower of 1998, when a maximum of 100 meteors per hour were observed. The shower is associated with Comet Pons-Winnecke, a short period comet that orbits the Sun every 6.37 years.
– The Quadrantids run from December 28th to January 7th, with its peak on the 3rd/4th when from 60 to 120 meteors per hour can be seen. It is associated with a suspected extinct comet, 2003 EH1, that is believed to have lost all of its ice, hence the absence of a notable tail. The Quadrantids are best observed from the northern hemisphere, although it has been seen north of latitude 51° South.