174 ASTRONOMYANDTHEBIBLE
velocityofArcturus, 257 milesasecond. Whatabout
itssize?
Ashas alreadybeenstated,Arcturusisthe fourth
orfifthbrighteststarintheheavens. Thisbrightness
isnotduetoitsnearnesstous. Forexample,Venus
is sometimes bright enough to be seen in daylight.
Thisisbecauseofitsnearness. Thelighttravelssuch
a short distance, comparatively, that itappears very
brighttous,whereasitisnotnearlysobrightasthat
ofthefaintestofthestars. Theyshinemorefaintly
because they are at such extremely great distances
fromus.
Arcturusshineswithaverybrilliantlight,butitis
veryfarfromus. Infact,itissofarthatastronomers
have notbeenableto getits distancewith anything
likeaccuracy. Theyknow,however,inageneralway,
somewhatnearitsdistance;thatis,theyknowthatit
is no nearer than certainmeasurements which they
havebeenabletomake. Howmuchfartherawayit
is,theycannotsay.
Basingtheirknowledgeonthiskindofgeneraliza-
tion, astronomers have concluded that Arcturus is
probablyathousandtimes larger than our ownsun.
Butoursunisnopygmywhencomparedwithsizes
familiartous. Wecangetsomeideaofhisbigness
ifwerealizethefollowing facts: Themoon makes
acircle abouttheearthatadistancefromtheearth
ofabout240,000 miles. Ifitwere possibletoplace
theearthinthecenterofthesun,withthemoonatthe
samedistancefromtheearthasnow,both theearth
andthemoonwouldbehiddenentirelywithintheball