When you’re out stargazing, you might notice some stars stand out because they are brighter and different in color to others. Most stars we see in space are ‘main sequence’ types, like our Sun. But, the stand outs are the ‘giants’. Here, I cover the different types of stars for your interest when you’re looking up at that night sky.
Three basic star types:
- Main Sequence (young stars)
- Giants (old large stars)
- Faint small (fading or dying)
You’ll notice these three types correspond to a stage of ‘life’. These stages aren’t necessarily all there is. The entirety is more of a tree, as depicted in the following diagram.
But for the sake of maintaining the interest of us budding astronomers, let’s keep it simple and centered on our night sky viewing…
Stellar classes and groups
Without getting too technical, here are the three main groups and subtypes I’ll cover here (plus a few more of interest)…
The main sequence types, like our Sun, fuse hydrogen to form helium in their cores.
Our Sun, estimated to be 4.6m years old, is a main sequence star and young, in astronomical terms. You might have guessed…it’s a yellow dwarf. Only a ‘young’ star, it’s estimated to last another 7 billion years, given its expected lifespan of about 10 billion (1010) years.
Spectral classes of O, B, A, F. G, K, and M also define the stars (using the Hertzsprung-Russell diagram). In this respect, our Sun is a G spectral class, just like Arcturus.
These G types have temperatures ranging between 4900 and 6800 Kelvin. The red dwarfs (in the K and M spectral classes) are cooler, reaching up to about 4500 K. And the Blue ones are the hottest of the lot.
If you’re like me, I think of blue as cool and red, hot. In this case…it’s the opposite.
Also, luminosity on this chart is measured relative to our Sun (value = 1). So 100 on the scale is 100x the luminosity of our Sun. It radiates a lot more energy in other words. I explain more on this and about absolute magnitude in my article on what to know about star brightness.
stars to locate in our night sky
Here I list the main stars in these groups for you. You may want to use your home telescope or binoculars with a star chart to locate some of them in the sky. Some you can do with your naked eye.
1. Main sequence dwarf Stars
These dwarf stars account for 90% of stars known in our Universe. They vary from blue to red, having a broad range of temperature and difference in luminosity relative to our Sun (see the Hertzsprung-Russell diagram).
Examples of dwarf stars to locate:
- Sirius A — blue-white (in constellation Canis major)
- Beta centauri — blue (one of the pointer stars, seen in southern hemisphere)
- Alpha Centauri A and B — yellow (part of the pointer stars, southern hemisphere)
- Barnards Star — red (in constellation Ophiuchus)
Sirius A is a main sequence dwarf in the blue-white spectral range. It’s the brightest star in the night sky, not necessarily the brightest object (see Jupiter, Venus, Mars, and Mercury). It is a spectral type A in the white spectrum range.
In the blue spectral range is Beta Centauri, which along with its ‘neighboring’ triple star Alpha Centauri (Alpha Centauri A, B, & C) is prominent in the southern hemisphere skies. These stars are what is known as the ‘pointer stars’ directing observers to the Southern Cross.
Both Sirius A and Beta Centauri can be seen by the naked eye and are easy ones to spot.
Alpha Centauri A and B look to us as a single bright star, unless using a telescope with which you should see them separated — This is a good one for kids to practice using their telescope.
Yellow dwarfs include Alpha Centauri A and B, Tau Ceti, and 51 Pegasi. Our Sun is also a yellow dwarf (but viewing the Sun through a telescope unshielded like with naked eyes is off-limits).
Barnard’s star: Named after the astronomer, E. E. Barnard, Barnard’s star is a low-mass red dwarf within our Milky Way.
Proxima Centauri (AKA Alpha Centauri C) is another example of a red dwarf. The red dwarfs are low mass stars, that are the longest-lived and the most common type of star in the Milky Way. But, they are not easily seen.
The place to point your telescope for observing Barnard’s Star is near the celestial equator. In the northern hemisphere, it is best seen in summer (June) high in the sky in the constellation Ophiuchus. Its neighbors are Sagittarius, Scorpius, and Libra.
Barnard’s Star is smaller and older than our Sun of 4.5 billion years old. It has been described as a flare star, which is one that has bursts of brightness at random but at relatively rare times, as in the one seen in 1998.
2. Giant Stars
A red giant star is a dying star. These types have run out of hydrogen.
Blue giants are large and extremely hot stars. They burn helium and are what follow on from the main sequence stage.
Yellow giants are the intermediates.
Examples of giants you can try and locate:
- Canopus — yellowish-white giant (in the constellation Carina, the Keel — a southern hemisphere constellation)
- Polaris Aa — yellow giant (northern hemisphere pole star in Ursa Minor)
- Arcturus — red giant (in the constellation Boötes, northern hemisphere)
- Aldebaran (Alpha Tauri) — red giant (in the constellation Taurus)
- Mira (Omicron Ceti) — red giant (in Cetus in the northern sky)
You might see Canopus in the northern hemisphere if you’re in the lower latitudes (roughly below +37).
Supergiant stars
Supergiants are the biggest and most luminous of the stars seen from Earth. Their temperature can range from about 3,450 K to over 20,000 K (red to blue spectrum).
Although rare and short-lived they are super bright.
Examples of supergiants to check out:
- Rigel — bluish white (in Orion)
- Deneb — bluish white (in Cygnus)
- Antares — red (in Scorpius, not to be confused with Mars)
- Betelgeuse — red (in constellation Orion)
You can see all of these with your naked eye.
Rigel and Deneb are the brightest stars in their respective constellations.
Betelgeuse is 1000x the size of and 14,000x brighter than our Sun.
Antares is less luminous than Betelgeuse but it stands out like Mars with its reddish hue.
3. Faint small
White Dwarfs
A white dwarf is a star that has exhausted its nuclear fuel. These are small dense stars comprised of carbon. Their surface temperatures are hot.
Sirius B is a white dwarf and can be found alongside it’s brighter companion Sirius A, a main sequence star, in the constellation, Canis Major. Sirius B is quite a hot little star in comparison to our Sun.
Neutron Stars
You’re not able to see these with the typical backyard instruments. These are very dense small celestial objects with a radius of about 12-18 miles (20-30 km), of mostly packed neutrons. They are thought to be a collapsed center, remnant of a giant star. It’s a stage at the end of the stars existence.
SR J0108-1431 in the constellation Cetus (the Whale), in the northern sky is the closest neutron star to us and is a pulsar…
Pulsar
Pulsar stars are neutrons that are highly magnetized and rotate, emitting a beam of electromagnetic radiation. The SR J0108-1431 in the constellation Cetus (the Whale) is an example, mentioned above and shown in the image here…
(Image: X-ray: NASA/CXC/Penn State/G.Pavlov et al. Optical: ESO/VLT/UCL/R.Mignani et al. Illustration: CXC/M. Weiss)
Brown dwarfs
A brown dwarf is a failed star. You’re not likely to see these, as UCLA astronomy professor, Ian Mclean explains: “Brown dwarfs are so elusive, so hard to find”.
And about them: “Brown dwarfs are the missing link between gas giant planets like Jupiter and small stars like red dwarfs”.
Some authorities group them as main sequence stars.
4. Others
Let’s look at others — the stars you might see mentioned and of interest.
Variable Stars
These stars are so named because they change in brightness (as seen from Earth). They are useful to observe, as I explain in my article on why you should target variable stars.
The reason they vary can be due to the star itself shrinking and expanding or because another celestial object eclipses it. There are around 42,000 variable stars.
Examples are R And in the constellation Andromeda, T Aqr in the constellation Aquarius. and the variable star, Mira (Omicron Ceti), in Cetus.
T tauri Star
This is a class of variable stars that are relatively young (< 10 million years). The temperature at the core of these is two low for hydrogen fusion. How are they powered? Gravitational energy driven by contraction of the star is their source of power.
The nearest T Tauri stars to us are in the Taurus molecular cloud in the constellations Taurus and Auriga, and the ρ-Ophiuchus (pronounced rho oh-fee-ook-ee) molecular cloud of the constellation Ophiuchus, both about 400 light years away. More than 200 T Tauri stars are estimated in the Rho-Ophiuchus molecular cloud.
Runaway Stars
A runaway star is one moving at a speed and direction through space abnormal to the surrounding interstellar matter, which includes the gas, dust, and cosmic radiation. An example of a runaway star is GD 50, which is a white dwarf star, smaller than our Earth by with slightly more mass than our sun.
Hypervelocity Stars
These are stars that move at high velocities. In 2005, one was recorded that moved at a velocity of 2 million mph. It was coined an ‘Outcast’ star, ejected by the Milky Way. They are associated with black holes.
Intergalactic Stars
These are sometimes termed rogue stars because they are not gravitationally bound to any galaxy.
Halo Stars
This is a group of globular clusters and field stars. These encircle the outer edge of spiral galaxies including the Milky Way in an area called the ‘halo zone’. They are thought to be the oldest stars in the galaxy.
Protostar
What is a protostar? As the name suggests (proto- meaning first or earliest), it is an early stage — a forming star. It’s basically a gas mass that’s contracting.
Final Thoughts
Hope you enjoyed these interesting facts about stars. There is so much to learn about the Universe. When you wish upon a star, what type will it be?
If you’re new here and starting out with astronomy, be sure to check out our Beginner’s Page where you will find helpful guides and tips to get more out of your stargazing experience.
Or, see our Buyer’s Guide Section if you are looking to buy astronomy gear and need some help sorting through the numerous options.
Info sources
Colors of the stars, see: www.vendian.org/mncharity/dir3/starcolor/ | CSIRO: Spectral Classes | NASA: Hubblesite | Space.com
