The Nearer Stars 
7 
4 — 6 j 
5. Long before parallactic motion was detected, it had been clear that 
such motion must necessarily be of very small amount. Early in the seventeenth 
century Kepler had maintained that the stars were merely distant suns; if so, 
the enormous difference between the intensities of sunlight and starlight 
could only be explained by supposing the stars to be millions of times as 
distant as the sun. Newton* pointed out that Saturn appears as bright as a 
first magnitude star, although its size is such that it can only re-emit by 
reflection about one part in ten thousand million of the total light emitted by 
the sun, and deduced that “ first magnitude ” stars, by which he meant the 
twenty or so brightest stars in the sky, must be about 100,000 times as 
distant as Saturn. This would assign to them a distance of about 90 million 
million miles, representing a parallax of 021 seconds of arc. The estimate 
was not a bad one; actually the twenty brightest stars in the sky have 
a mean parallax of 0T34 seconds. Immediately after this Bradley attempted 
to measure the parallax of y Draconis, and although he failed to achieve his 
primary aim, he proved conclusively that the star’s parallax was less than 
a second of arc. 
6 . Not until 1838 was the great gulf definitely bridged; in that year 
Bessel, Struve and Henderson independently found unmistakable positive 
Table I. Stars within five parsecs of the Sun. 
Star 
Parallax 
Distance in 
parsecs 
1 
Proxima Centauri 
0-765 
1-31 
2 
a Centauri 
0-758 
1*32 
3 
Munich 15040 
0-538 
1-86 
4 
Wolf 359 
0-404 
2-48 
5 
Lalande 21185 
0-392 
2-55 
6 
Sirius 
0-377 
2-65 
7 
B.D. -12°, 4523 
0-350 
2-86 
8 
11 h. 12-0 m., -57-2 
0-340 
2*94 
9 
Cordoba 5 h. 243 
0-317 
3-16 
10 
t Ceti 
0-315 
3-17 
11 
Procyon 
0-312 
3-21 
12 
« Eridani 
0-310 
3*23 
13 
61 Cygni 
0-300 
3-33 
14 
Lacaille 9352 
0-292 
3-42 
15 
Struve 2398 
0-287 
3-48 
16 
Groombridge 34 
0*282 
3-55 
17 
t Indi 
0-281 
3-56 
18 
Kruger 60 
0-256 
3-91 
19 
0 h. 439 m., +4 - 55 
0*255 
3-92 
20 
Lacaille 8760 
0-253 
3*95 
21 
2 h. 50 3, +52-1 
0-239 
4-18 
22 
23 h. 59 5, -37-9 
0-220 
4-55 
23 
17 h. 37-0, +68-4 
0-213 
4-69 
24 
10 h. 14-2, +20-4 
0-207 
4-83 
25 
Altair 
0*204 
4-90 
26 
o -2 Eridani 
0-203 
4-93 
* System of the World (1727).