Sky & Telescope - May 2020 - 47

Venus falls from view, Mercury gains
altitude on its way to its greatest elongation from the Sun on June 4th.

December
solstice

Uranus

LATE EVENING TO DAWN
Jupiter and Saturn appear within 5°
of each other all May, shining just on
either side of the Sagittarius-Capricornus border (Jupiter in Sagittarius, Saturn in Capricornus). As Earth begins to
overtake them in the race of the three
planets around the Sun, Saturn appears
to halt its direct (eastward) motion on
the 11th, as does Jupiter on the 14th.
Then both begin to retrograde (move
westward relative to the background
stars). The tightest pairing of the two
occurs on May 18th when Jupiter is 4.7°
west-southwest of Saturn.
This qualiﬁes as a "quasi-conjunction" (an event in which two objects
don't share the same right ascension
or ecliptic longitude yet reach a minimum separation of 5° or less from each
other). After this date, faster Jupiter
begins to move away from Saturn, but a
few months from now the two will start
to converge again as they head toward
their ultra-close true conjunction on
December 21st.
Both Jupiter and Saturn rise around
1:30 a.m., daylight saving time, as May
begins and around 11:30 p.m. as the

Mercury

Sun

Jupiter

Neptune

Earth
June
solstice

The curved arrows show each planet's movement during May. The outer planets don't change
position enough in a month to notice at this scale.

month comes to an end. During May,
Jupiter brightens slightly from magnitude -2.4 to an even more impressive
-2.6, and Saturn increases from magnitude 0.6 to 0.4.
This month, Jupiter and Saturn are
highest, and therefore usually sharpest
in telescopes, during morning twilight.
Jupiter's apparent equatorial diameter
grows from about 41″ to 45″ in May.
Saturn's disk is a little more than 17″
across, while its rings span about 37″
edge-to-edge and are tilted just under
21° from edgewise - a little shy of their
27° degree maximum.

Dusk, May 23 - 24

30 minutes after sunset

30 minutes after sunset
Capella

Capella

` Tau
Mercury

ζ Tau

β Tau
Venus
Moon
May 23

Looking West-Northwest

PRE-DAWN AND DAWN
Mars rises a little before 3 a.m. as May
opens, and about an hour sooner as
the month closes. At the same time,
the plane t brightens from magnitude 0.4 to 0 and its disk grows from
7.6″ to 9.2″ in diameter. Mars shines
about one degree north-northwest of
magnitude 3.6 Gamma (γ) Capricorni
(Nashira) on May 1st, and the same
distance north of magnitude 2.8 Delta
(δ) Capricorni (Algedi) on the 4th. The
Red Planet glides from Capricornus
into Aquarius on the 9th.
Neptune rises a little before the start
of morning astronomical twilight, while
Uranus remains lost in the Sun's glare
most of May, only emerging at dawn in
the ﬁnal week of the month. Neither
planet is well-placed for observation.

MOON PASSAGES

Moon
May 24

Venus

Mars

ORBITS OF THE PLANETS

Dusk, May 22

c Tau

Venus

Saturn

tq These scenes are drawn for near the middle of North America (latitude 40° north, longitude
90° west); European observers should move each Moon symbol a quarter of the way toward the
one for the previous date. In the Far East, move the Moon halfway.

Mercury

Sept.
equinox

March
equinox

Looking West-Northwest

The Moon is a waxing gibbous a few
degrees above Regulus at nightfall on
May 1st. The waning gibbous Moon is
a few degrees below Jupiter at dawn on
the 12th. The last-quarter Moon is several degrees to the right of Mars on the
14th. About 30 minutes after sunset on
the 23rd, a very thin lunar crescent is
less than ﬁve degrees to the lower left of
Venus, with Mercury a similar distance
to the upper left of Venus.
¢ FRED SCHAAF teaches astronomy at
both Rowan University and Rowan College in southern New Jersey.
s k y a n d t e l e s c o p e . o r g * M AY 2 0 2 0

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Sky & Telescope - May 2020

Table of Contents for the Digital Edition of Sky & Telescope - May 2020