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Exoplanet Star

Annulus Aperture

0. 5 ° diuser

T 1 = 1. 720 E 6

C 2 = 1. 675 E 6

54 ASTRONOMY • JUNE 2020

With the right equipment and techniques, finding

these elusive objects is easier than you think.

BY JERRY HUBBELL

DISCOVER

EXOPLANETS

from your backyard

or anyone who grew

up reading science fic-

tion or watching Star

Tre k, the existence of

planets outside our

solar system was a

given. We took it for

granted that there must be

millions of these star systems

— but we didn’t have proof.

Then, in 1995, Michel

Mayor and Didier Queloz

at the University of Geneva

announced their discovery of

extrasolar planet 51 Pegasi b

orbiting a G2 star about

50 light-years from Earth.

This watershed event spurred

a renaissance in planetary

science and captured the

imaginations of people all

over the world.

I’ve always wanted to do

science with my telescope, but

only in the last 10 years has

the technology been available

to get serious about studying

exoplanets with it. Today, just

about anyone can make pre-

cise measurements of stars

from their backyard. I wanted

to learn asteroid imaging and

astrometry — the precise

measurement of minor planet

positions in the sky. Then I

began learning how to do

photometric (brightness)

measurements with tools

freely available on the inter-

net. Measuring brightness

F

When an exoplanet transits (crosses in front of) a star from our

point of view, the amount of light we receive decreases. Sensitive

equipment can record this drop, revealing properties of the

transiting exoplanet. ASTRONOMY: ROEN KELLY

Aperture photometry requires two measurements: one of the star

(the aperture) and the other of a ring of sky (the annulus) around

the star. Subtracting the brightness of the annulus from that of the

aperture gives the star’s true brightness. JERRY HUBBELL

CATCH A PLANET STARLIGHT MINUS SKY