Star	type	Distance in light years	Apparent brightness as multiple of brightness of Sun if it were at a distance of 32.6 light years (10 parsec)	Absolute brightness: actual power emitted as multiple of power from Sun 	
Sun	Ordinary yellow star	If moved to a distance of 32.6 light years (10 parsec)	1	1 	
The ‘Summer Triangle’ of three bright stars high in the summer sky 	
Altair 	Quite nearby white star	16	42	10 approximately 	
Vega	Quite nearby bright blue-white star	25	83	49 	
Deneb	Distant blue-white supergiant. One of the most luminous naked eye stars known	1630	26	65 000 	
The two brightest stars in Orion the Hunter, and Sirius the 'Dog Star' near Orion 	
Betelgeuse	Very large unstable red giant, diameter 300 – 400 × Sun	1040	54	55 000 	
Rigel	Blue-white supergiant	864	76	53 000 	
Sirius	Nearby bright white star	8.64	330	23 	
The Pole Star 	
Polaris 	Yellow supergiant Cepheid variable	360	13	1600 	
Three red giants. Antares is the red ‘eye’ of the scorpion in Scorpio. Aldebaran is the red eye of the bull in Taurus. Arcturus is the 4th brightest star in the sky, and may be like the Sun will be at a later stage of its evolution 	
Antares	Red supergiant, diameter 300 × Sun	619	35	13 000 	
Arcturus	red giant, mass similar to Sun, diameter 27 × Sun	33	88	90 	
Aldebaran	Red giant	62	39	141	
 
Data adapted from J B Kaler ‘Stars’ Scientific American Library 1992 
You are going to show that these stars vary very greatly in how much light they actually emit.  
Brighter stars aren’t always nearer
Question 46S: Short Answer		

Can the brightness of stars indicate their distance? 
If all stars shone equally brightly, the ones that are further away would look fainter. But if stars vary a lot in actual brightness, how bright they look is a poor guide to how far away they are. Here you calculate actual brightnesses from how bright stars look and how far away they are. 
A selection of well-known stars 
If the Sun were a typical fairly nearby star in the sky, it would be rather faint, in fact only just visible to the naked eye. In the table below, the brightness of the Sun as it would look on Earth if it were 10 parsecs (32.6 light years) away, is arbitrarily taken as 1 unit. Other apparent brightnesses are given as multiples of this standard brightness. The stars listed are all amongst the brightest-seeming stars in the night sky of the northern hemisphere. They all therefore give out more light than the Sun. 

Print out the table to answer the following questions. 
1.	List the stars in order of their distance from us, from nearest to furthest. 

2.	List the stars in order of how bright they appear, from brightest to faintest. 

3.	Remember that in the comparisons the Sun’s apparent brightness at a ‘standard distance’ of 32.6 light years (10 parsec) is taken as 1. Notice that Altair is almost exactly half this distance away (16 light years). By what factor would Altair’s apparent brightness decrease if it were twice as far away, at the ’standard distance’? 

4.	Show that Altair emits about 10 times more light than the Sun. 

5.	Deneb is the most distant of these stars, at 1630 light years. If it were at the ‘standard distance’ of 32.6 light years, how many times brighter would it appear than it now does? 

6.	Show that Deneb emits between 50 000 and 100 000 times more light than the Sun. 

7.	Sirius is one of the brightest looking stars in the sky. The Pole Star Polaris is not remarkably bright. Show from the data that Polaris emits more than 50 times as much light as Sirius. 

8.	After Deneb, which two stars are the next most powerful emitters of light? 

9.	Aldebaran is about twice as far away as Arcturus, and appears roughly half as bright. What inference can you draw about the ratio of the amounts of light they emit? 

10.	List these stars in order of their actual brightness (the amount of light they emit).