My first Magazine Sky & Telescope - 04.2019 | Página 50

APRIL 2019 OBSERVING
Celestial Calendar by S. N. Johnson-Roehr
An April
Asteroid
14 h 00 m
14 h 10 m
13 h 50 m
May
2
30
28
26
Try to catch 2 Pallas as it
skims through the northern
sky this month.
22
20
18
A PR I L 2 019 • SK Y & TELESCOPE
+20°
16
C
48
+22°
24
BOÖTES
onditions are ideal for viewing
asteroid 2 Pallas as it eases its way
across Boötes this month. Opposition
falls on April 6th, just 32 hours after
new Moon; however, Pallas is well
placed for observation in the weeks pre-
ceding and following that date as well.
Pallas spends most of March and April
just 1.6 astronomical units from Earth,
making its closest approach March
29–30, and rises to a peak brightness
of 7.9 on March 20th. Look for it to
remain that bright through April 14th.
After that date, it slowly dims, dropping
to magnitude 8.5 by May 11th. Pallas
won’t approach naked-eye visibility any
time soon (it’s not predicted to bump
up to an estimated magnitude 6.6
before March 2028), but even at magni-
tude 8.5 it’s well within reach of 10×50
binoculars and small telescopes.
Pallas was fi rst detected by the
German astronomer Heinrich W. M.
Olbers. Trained as a physician, Olbers
was also a dedicated astronomer who
spent his nights observing from the
upper fl oor of his home in Bremen (bay
windows gave him a clear view to the
south, and he knocked holes in the
roof to allow zenithal observations).
On March 28, 1802, he passed some of
the evening studying Ceres, the only
asteroid known at that point, through
his Dollond refractor. Those observa-
tions completed, he turned his telescope
to the adjacent sector of sky. To his
surprise, he almost immediately spot-
ted a star where he knew none should
13 h 40 m
_
Arcturus
14
12
10
d
+18°
8
o
April
2
4
p
+16°
6
31
29
27
+14°
25
23
3
4
5
6
7
8
9
21
+12°
19
17
Mar
15
+10°
Asteroid 2 Pallas follows a shallow arc across southwest Boötes in April.
Use the 3rd-magnitude star Eta (η) Boötis to locate the asteroid near the
date of opposition.