How Many Times Must A Man Look Up? Quiz

Answer: Canis Major

How many times must one look up to the night sky to find Sirius? Well: once is enough, if there are not too many clouds or too many light pollution. Sirius appears at the night sky as the brightest star of all, with an apparent magnitude of -1.46. Its absolute magnitude is +1.42, compared to +4.83 for our Sun - meaning that if they were on the same distance, Sirius would be approximately 23 times brighter.

Sirius is nicknamed the Dog star, as its rise in the night sky is most prominent in the dog days of summer (start of August). The official name of Sirius is Alpha Canis Majoris. Sirius is the brightest star of the constellation Canis Major (the Greater Dog).

You can find Sirius at a right ascension of 6h 45m 08.917s and a declination of -16° 42' 58.02". These indications are to be interpreted as follows. Suppose you're at the earth's equator at the vernal equinox (March 21), when the sun crosses the celestial equator. Then the right ascension is the angle to look for the star you want to find (and can thus be compared with the terrestrial longitude). The declination on the other hand is the highest point the star reaches, thus perpendicular to the right ascension. You can compare the declination to the terrestrial latitude: if for instance a star would be at a declination of +40°, it would be almost exactly overhead an observer on the terrestrial latitude of 40° north.

In fact Sirius is part of a double star: the twin star Sirius B is almost at the same location, but very faint (with a magnitude of 8.44). It has been calculated that both Sirius A and Sirius B were originally blue stars (the brightest stars in the universe), but about 120 million years ago Sirius B exploded to a red giant and then blew its outer shell, with only a white dwarf remaining. (Blue means the highest surface temperature, over 33,000 Kelvin. It then descends to white, yellow, orange and red).

Sirius is about 8.6 light years away (a light year is the distance travelled by light in a vacuum in one year time, at a speed of 300,000 km per second or 186,000 miles per second). In the same constellation are several other named stars, but at very different distances. For instance Epsilon Canis Majoris is at a distance of 430.5 light years and thus, even if it has absolutely more luminous power than Sirius, is far less visible. So a constellation is a number of stars roughly in the same direction, but they don't belong together if you take into account the relative distance.

Answer: Centaurus

In 1603 the astronomer Johann Bayer devised a classification of stars by preceding the name of their constellation by a Greek letter. Thus Alpha Centauri is the first star in the constellation Centaurus.

Alpha Centauri is a set of three stars with a common centre of gravity. Alpha Centauri A has a right ascension of 14h 39m 36.494s and a declination of -60° 50' 02.3737". Because of its proximity to the earth (only 4.36 light years) it has a high apparent magnitude (-0.27 for the combination of Alpha Centauri A and Alpha Centauri B).

Alpha Centauri B is slightly further (4.40 light years) and the third star in this cluster, Proxima Centauri, is the closest star to our solar system, at 4.24 light years. While Alpha Centauri B is an orange star with a surface temperature of 3,900 to 5,300 Kelvin and Alpha Centauri A is a yellow star as our Sun (surface temperature between 5,300 Kelvin and 6,000 Kelvin), Proxima Centauri is only a red dwarf with a surface temperature less than 3,900 Kelvin.

Proxima Centauri has at least two planets circling the star: an earth-sized planet in the habitable zone and a smaller planet nearer to the star. Alpha Centauri is the third brightest star in the night sky. Beta Centauri is another star in the same constellation (thus more or less found in the same direction), but much further at 525 light years.

Answer: Boötes

Arcturus is the brightest star in the constellation Boötes (the Plowman). Arcturus is an orange star at a distance of 37 light years and with an apparent magnitude of -0.05. You can find it at a right ascension of 14h 15m 40.35s and a declination of +19° 11' 14.2".

On average, Arcturus is the fourth brightest star at the night sky. While Arcturus has an almost constant apparent magnitude, the next in the list has a variable apparent magnitude that occasionally exceeds Arcturus' magnitude. The next brightest star in Boötes, with an apparent magnitude of 2.37, is much further away, at 236 light years.

Answer: Lyra

Vega is one of the best studied stars outside of our solar system. It once had the function of Polaris (indicating the geographical north), about 12,000 BCE, and will once again fulfil this function around 13,727 AD.

Vega, also named Alpha Lyrae, is the brightest star of the constellation Lyra. You can find it at a right ascension of 18h 36m 56.19s and a declination of +38° 46' 58.8". It has an average apparent magnitude of +0.03 (with variations from -0.02 to +0.07) and is about 25 light years away. Vega is a white star, thus presenting a surface temperature higher than our Sun (7,300 to 10,000 Kelvin).
On average Vega is the fifth brightest star in the night sky.

Other visible stars in the constellation Lyra are much further away: for instance Gamma Lyrae is at 634 light years and Beta Lyrae at 881 light years.

Answer: Orion

Despite the very large distance (773 light years), Rigel (also known as Beta Orionis) is a quite bright star. Rigel has an apparent magnitude of +0.18 and can be found at a right ascension of 5h 14m 32.27s and a declination of -08° 12' 05.9". Rigel is a bluish-white star at the "left foot" of the constellation Orion (which resembles a warrior). On average Rigel is the seventh brightest star in the night sky.

Other noteworthy stars in the constellation Orion include Betelgeuse, a red star with an apparent magnitude of +0.42 at a distance of 643 light years, and Bellatrix, a bluish-white star with an apparent magnitude of +1.64. Betelgeuse is at the "right hand" of Orion, and Bellatrix is the "left shoulder" of Orion.

Answer: Aquila

Altair is scientifically known as Alpha Aquilae, the first star in the constellation Aquila (the Eagle). You can find this white star at a distance of only 17 lightyear at the right ascension 19h 0m 46.68s and declination +08° 52' 02.6". Altair has an apparent magnitude of 0.77. On average Altair is the twelfth brightest star in the night sky.

Altair is nowadays considered a very young star, only 100 million years old. In comparison our Sun is middle-aged at about 4.6 billion years old. Other stars in the constellation Aquila include Gamma Aquilae at a distance of 460 light years and Zeta Aquilae at a distance of 83 light years.

Answer: Taurus

Aldebaran (also known as Alpha Tauri) is a red giant in the constellation Taurus (the Bull), and is about 65 light years away. You can find Aldebaran at a right ascension of 04h 35m 55.20s and a declination of 16° 35' 30.01". Aldebaran has an apparent magnitude of 0.87, which makes it the 13th star visible in the night sky.

Although not all astronomers agree, Aldebaran is supposed to have at least one planet - a planet estimated almost six times the size of Jupiter, but in the habitable temperature zone.

Other interesting stars in the constellation Taurus are part of the Pleiades star cluster: Alcyone A (half of a binary star) at a distance of 368 light years and Atlas A (part of a triple star) at a distance of 380 light years.

Answer: Scorpius

Antares is a red supergiant in the constellation Scorpius, with an apparent magnitude of 0.91. As the brightest star in Scorpius, its scientific name is Alpha Scorpii. On average, Antares is the 16th brightest star in the night sky. You can find Antares at a right ascension of 16h 29m 24.47s and a declination of -26° 25' 55.0". It is about 553 light years away.

Antares has been calculated to be a double star, but the location of its twin is highly disputed.

Scorpius has many other stars visible to the naked eye (apparent magnitude +6,50 or brighter), at distances varying from 23 light years to 5,900 light years.

Answer: Virgo

Spica is the brightest star in the constellation Virgo (the Virgin), with an apparent magnitude of 0.98. That makes it on average the 16th brightest star in the night sky.

Spica appears as a blue or bluish-white giant (or perhaps a subgiant), but in fact it is a binary star spinning very rapidly: both stars orbit their common centre of gravity each four days. These two stars are so close one can only conclude the existence of the twin star by slight aberrations on the measured qualities - even the most sophisticated telescopes cannot distinguish the twin stars.

Spica is about 250 light years away and can be found at a right ascension of 13h 25m 11.60s and a declination of -11° 09' 40.5". Other stars in the constellation Virgo that can be seen with the naked eye, are at distances varying from 28 light years to a whopping 1,294 light years.

Answer: Gemini

Pollux, with an apparent magnitude of 1.16, is the brightest star in the constellation Gemini and, on average, the 17th brightest star in the night sky. Pollux is named Beta Gemini, whereas Castor is Alpha Gemini. At a distance of 34 light years, you can find Pollux at the right ascension 7h 45m 19.36s and the declination +28° 01' 34.7".

Pollux is an orange-red giant. Previously it was probably a white star, but when the hydrogen was almost completely exhausted, Pollux expanded to a giant star and cooled to orange-red.

Although this is still a matter of discussion, many astronomers suppose that Pollux has at least one planet, about 2.3 times the size of Jupiter.

One of the other stars in the constellation Gemini is the binary star Castor, at about 52 light years.