SKY_July2014.pdf

Alan MacRobert

SkyandTelescope.com July 2014 51

Learn how to use detailed star charts to fi nd the faintest things with your telescope: skypub.com/charts.

live near 40°° north latitude.

Mars and Spica are your naked-eye starting points, as

shown on the wide-fi eld chart at left. Mars and Spica are

14 ° apart on American evening of June 1st, 5½° on July

1st, and 1.3° on July 13th, their own date of least angular

separation (appulse).

Quite near the two asteroids on the sky, though utterly

invisible from Earth, is NASA’s Dawn spacecraft. It’s

en route from its successful 2011–12 mission at Vesta to

its next mapping project at Ceres, where it will take up

permanent orbit in spring 2015.

Although the two asteroids look close together, they

June 26

27

28

29

30

July

1 2 3 4 5 6 7 8 9

10

June

26

27

28

29

30

July

1 2 3 4 5 6 7 8 9

10

c

VIRGO

Pa

th

o

f^ V

es

P ta

at

h^

of

C

er

es

13 h 36 m 13 h 32 m 13 h 28 m 13 h 24 m

–2°

–1°

Star magnitudes

4 5 6 7 8 9

10

11

Vesta is 7th magnitude and Ceres is 8th as

they swing together near Mars and Spica. The

date ticks are plotted for 0:00 Universal Time.

Interpolate to put a pencil mark on each of the

paths for the date and time you plan to look.

Opposite page: Stars are plotted to magnitude

9.0 and galaxies (in the Virgo Cluster) to 11.5.

Third-magnitude Gamma (γ) Virginis is an equal

double star with a current separation of 2.1′′.

The black rectangle shows the area of the close-

up chart on this page.

Ceres and Vesta Paired

Date (0 mag. mag.h UT) Ceres Vesta Separation

May 1 7.2 6.0 2.6°

June 1 7.8 6.6 2.1°

July 1 8.4 7.1 0.4°

Aug. 1 8.8 7.4 2.2°

Sept. 1 9.0 7.7 5.0°

Ceres

mag.

7. 2


8. 8
   8.4


9. 8
   9.0

Separation

2. 6 °°
   2.1°°


3. 4 °°
   2.2°°


4. 0 °°

JULY METEORS

Several minor, long-lasting meteor showers with radi-

ants in the southern sky are active in July, including the

Alpha Capricornids, Piscis Austrinids, and Delta Aquari-

ids. Together they increase the chance that a meteor you

see late on a July night will be fl ying out of the south.

On the morning of July 19th, the faint asteroid

611 Valeria will black out an 8.7-magnitude star in

Pisces for up to 4 seconds as seen from a track

predicted to cross northern Mexico, Texas, the

Deep South (including the Atlanta area), and the

Carolinas. The occultation will happen within

a couple minutes of 9:10 UT in Texas and 9:12

UT in the Carolinas, where dawn will be getting

under way.

For a map, fi nder charts, more about asteroid

occultations, and additional predictions, see

skypub.com/july2014asteroidoccultation.

Asteroid Occultation

are not. Ceres is a good 46 million miles (74 million km)

in the background of Vesta around their appulse date.

That’s part of the reason why Ceres looks fainter. Ceres,

with a diameter of 585 miles (940 km), is actually almost

twice as large as Vesta. But it’s farther from the Sun as

well as from Earth, and it has much darker surface mate-

rial. Vesta is medium-gray, refl ecting 42% of the sunlight

striking it (a high albedo for an asteroid), whereas Ceres

is a more typical dark gray-brown with an albedo of only

9%. But patchy brighter and darker markings on Ceres,

revealed in Hubble images, hint of interesting landscapes

awaiting Dawn.

DAVID MAYHEW