Sigma2 Cancri Star Facts (Distance, Colour & more)

Sigma2 Cancri is a Subgiant Star that is located in the constellation of Cancer. Based on the spectral type (A7IV) of the star, the Sigma2 Cancri colour is blue - white . It is not part of the Cancer constellation outline but is within the borders of the constellation.

The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

Sigma2 Cancri is located in the Milky Way galaxy, this is the galaxy that you reside in. In case you're wondering, Sigma2 Cancri is not located within the Solar System, there is only one star in the Solar System and that is the Sun.

There are no known exoplanets in orbit round the star, there might or might not be any but due to their size compared to the star, they'll be very hard to spot compared to other smaller stars hence why none have been spotted around a supergiant.

No one has visited Sigma2 Cancri and we have no probes on a rendezvous with the star.

Sigma2 Cancri is a Binary or Multiple star system.

Using the most recent figures given by the 2007 Hipparcos data, Sigma2 Cancri distance from Earth is 194.26 light years. When you look at Sigma2 Cancri, you are in fact looking back in time, you are seeing how it looks years ago. Roughly, change the distance from light years to years, that will tell you how long ago we are looking at the star.

Sigma2 Cancri Location

The location of the subgiant star in the night sky is determined by the Right Ascension (R.A.) and Declination (Dec.), these are equivalent to the Longitude and Latitude on the Earth. The Right Ascension is how far expressed in time (hh:mm:ss) the star is along the celestial equator. If the R.A. is positive then its eastwards. The Declination is how far north or south the object is compared to the celestial equator and is expressed in degrees. For Sigma2 Cancri, the location is 08h 56m 56.63 and +32° 54` 38.1 .

Sigma2 Cancri Radial Velocity and Proper Motion

Sigma2 Cancri Proper Motion

All stars like planets orbit round a central spot, in the case of planets, its the central star such as the Sun. In the case of a star, its the galactic centre. The constellations that we see today will be different than they were 50,000 years ago or 50,000 years from now. Proper Motion details the movements of these stars and are measured in milliarcseconds. The star is moving -66.13 ± 0.15 milliarcseconds/year towards the north and -53.49 ± 0.29 milliarcseconds/year east if we saw them in the horizon.

Sigma2 Cancri Radial Velocity

The Radial Velocity, that is the speed at which the star is moving away the Sun is 5.30000 km/s with an error of about 2.80 km/s . When the value is negative then the star and the Sun are getting closer to one another, likewise, a positive number means that two stars are moving away. Its nothing to fear as the stars are so far apart, they won't collide in our life-time, if ever.

Sigma2 Cancri Physical Properties

Sigma2 Cancri Colour

Based on the star's spectral type of A7IV , Sigma2 Cancri's colour and type is blue - white subgiant star.

There is no relationship between colour and size, a red star can be both the largest and the smallest stars in the Universe. Small stars are more energy efficient than larger stars and live longer.

Sigma2 Cancri Temperature

Based on the spectral type as we don't have the exact temperature', we can deduce that the surface temperature of the star is in the order of 7,500 and 10,000K based on the notes from Harvard University. To put this in context, the temperature of our Sun is about 5,778 Kelvin as said by Google.

• Blue (O) > 25,000K
• Blue/White (B) = 10,000 - 25,000K
• Blue/White (A) = 7,500 - 10,000K
• Yellow/White (F) = 6,000 - 7,500K
• Yellow (G) = 5,000 - 6,000K
• Orange/Red (K) = 3,500 - 5000K
• Red (M) = < 3,500K
• Red (C) = < 3,500K

There is a relationship between colour and temperature, stars that are closer to red in the rainbow spectrum are cooler whereas those closer to blue are hotter. Those that are blue stars are normally identified as being young stars whereas redder stars are usually older stars, ones that are at the end of their life. An example of when its a Blue Straggler, the star has stolen matter from a nearby star and grown to appear youthful when its not. These stars are found mainly in Star Clusters.

Sigma2 Cancri Luminosity

Luminosity is the amount of energy that a star pumps out and its relative to the amount that our star, the Sun gives out. Our star, the Sun's value is 1. ' The figure of 19.68 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012. The star generates more energy than our star.

Sigma2 Cancri Radius

Sigma2 Cancri estimated radius has been calculated as being 2.437 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,695,620.282.km. If you need the diameter of the star, you just need to multiple the radius by 2. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 2.426. The figure is derived at by using the formula from SDSS rather than peer reviewed papers. It has been known to produce widely incorrect figures.

Sigma2 Cancri Apparent (Brightness) and Absolute Magnitudes

Absolute Magnitude is the apparent magnitude of the star from a distance of 10 parsecs or 32.6 light years. This assumes that there is nothing in between the object and the viewer such as dust clouds. To really compare the brightness of the star, it is best to use Absolute rather than Apparent Magnitude.

Magnitude, whether it be apparent/visual or absolute magnitude is measured by a number, the smaller the number, the brighter the Star is. Our own Sun is the brightest star and therefore has the lowest of all magnitudes, -26.74. A faint star will have a high number.

Sigma2 Cancri apparent magnitude is 5.44, this is a measure of the brightness of the star as seen from Earth. Apparent Magnitude is also known as Visual Magnitude. If you used the 1997 Parallax value, Sigma2 Cancri absolute magnitude is 1.56 If you used the 2007 Parallax value, Sigma2 Cancri absolute magnitude is 1.57.

Visible from Earth

Sigma2 Cancri is visible from Earth. The lower the Apparent Magnitude of a star or other object is, the easier it is to see in the night sky. An object with a magnitude greater than 6.5 can not be seen without the aid of a telescope or other device.

Sigma2 Cancri Distance from Earth

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 16.73000 which means Sigma2 Cancri distance from Earth is 194.96 light years away from Earth or 59.77 parsecs. If you want that in miles, it is about 1,146,096,802,755,876.606, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 16.79000 which puts Sigma2 Cancri distance from Earth as 194.26 light years or 59.56 parsecs. It should not be taken as though the star is moving closer or further away from Earth. It is purely that the distance was recalculated.

Using the 2007 distance, the star is roughly 12,285,046.257 Astronomical Units from the Earth/Sun give or take a few. An Astronomical Unit is the distance between Earth and the Sun. The number of A.U. is the number of times that the star is from the Earth compared to the Sun. The star's Galacto-Centric Distance is 7,445 Parsecs or 24,282.861 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

Alternative Names and Meanings

• Sigma2 Cancri (Sig02 Cnc) is the Bayer Classification for the star. The Bayer Classification was created by Johann Bayer in 1603. The brightest star in the constellation is normally given the Alpha designation, there are exceptions such as Pollux which is Beta Geminorum.
• The Id of the star in the Yale Bright Star Catalogue is HR3555.
• HIP43932 is the reference name for the star in the Hipparcos Star Catalogue.
• The Id of the star in the Henry Draper catalogue is HD76398. The catalogue was started by the American doctor and has been expanded on over the years.
• The star is catalogued in the Tycho-2 star catalogue as TYC-2488-1707-1. The catalogue lists 2 millions stars and its homepage is E.S.A.
• Flamsteed designations such as 59 Cancri (59 Cnc) are named after the creator, Sir John Flamsteed. Sir John named the stars in the constellation with a number and its latin name, this star's Flamsteed designation is 59 Cancri. The Flamsteed name can be shortened to 59 Cnc.
• BD number is the number that the star was filed under in the Durchmusterung or Bonner Durchmusterung, a star catalogue that was put together by the Bonn Observatory between 1859 to 1903. The star's BD Number is BD +33 1785.

Sigma2 Cancri Travel Time

The time it will take to travel to this star is dependent on how fast you are going. U.G. has done some calculations as to how long it will take going at differing speeds. A note about the calculations, when I'm talking about years, I'm talking non-leap years only (365 days).

The New Horizons space probe is the fastest probe that we've sent into space at the time of writing. Its primary mission was to visit Pluto which at the time of launch (2006), Pluto was still a planet.

Mach 1 is the speed of sound, Mach 2 is twice the speed of sound. Corncorde before it was retired was the fastest commercial airline across the Atlantic and only one that could do Mach 2.

Description	Speed (m.p.h.)	Time (years)
Walking	4	32,568,496,587.385
Car	120	1,085,616,552.913
Airbus A380	736	177,002,698.844
Mach 1	767.269	169,789,195.64
Mach 2	1,534.54	84,894,487.175
New Horizons	33,000	3,947,696.556
Speed of Light	670,616,629	194.26

Source of Information

The source of the information if it has a Hip I.D. is from Simbad, the Hipparcos data library based at the University at Strasbourg, France. Hipparcos was a E.S.A. satellite operation launched in 1989 for four years. The items in red are values that I've calculated so they could well be wrong. Information regarding Metallicity and/or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.

}