Table of Contents

2018, June 1: #Mars Observations

From Astronomy Picture of the Day

From Robert C. Victor


This is dated material. Some of the events happen this week. Please share with others who may be interested. Thank you!

Skywatchers in midwestern U.S.,

On most of the last several mornings, I have taken my 6-inch Orion Dobsonian reflector outdoors during the couple of hours before sunrise, and used a 6-mm eyepiece (providing a magnification of 200-power) to observe Mars and Saturn. The south polar cap of Mars was immediately obvious!

The Martian southern hemisphere spring equinox occurred on May 22, so the polar cap is still near its maximum extent. I also noticed some dark markings on the disk, near the equator and southern latitudes, and a bright area near the following or morning (celestial east, Martian west) limb, which may have been morning frost or morning clouds. And at the northern limb, I noticed a very narrow bright area that could have been the edge of the northern polar hood of clouds. The north pole itself is tipped away from Earth by 15 degrees.

Keep in mind that as spring progresses in the Martian southern hemisphere, the southern polar cap will shrink rapidly, so if you wait until Mars becomes conveniently visible in the evening, a much smaller polar cap will remain. Opposition and closest approach of Mars will occur in the last week of July, but don’t wait until then!

In coming days, two of the most striking markings on Mars (in addition to the South Polar Cap) will be in excellent position as seen from the eastern U.S. in the hours before dawn, when Mars is highest in the southern sky.

The markings are (1) Syrtis Major, which displays a dark triangular shape resembling a northward-pointing India, centered just north of the Martian equator. Also at the same Martian longitude (290 degrees) is (2) Hellas Basin, which often appears very bright because of haze or surface frost deposit. Hellas is centered near lat. 42 degrees south and so appears between Syrtis Major and the South Polar Cap.

Currently, any particular Martian surface feature reaches the central meridian of Mars a little over 38 minutes later each day. So if you observe Mars at the same time each morning, a feature will first appear near the sunset terminator, near the celestial west limb of Mars where the solar illumination cuts off. (You’ll notice in early June that Mars appears not round, but in gibbous phase.) Each successive day at the same time, the Martian feature will move farther back from the sunset terminator, eventually passing near the center of the disk, and continuing on toward the morning (celestial western) limb. In each 24 hours, Mars makes less than one complete rotation.

Here are times (in CDT) when the longitude of the central meridian of Mars is equal to 290 degrees. At these times, Syrtis Major will appear a little north of the center of the Martian disk, and Hellas will appear well south of the disk center. Even if you observe up to three hours away from these times, the east-west foreshortening of these features will be less than 50 percent, but you’ll not want to observe too many hours before Mars reaches your local meridian — it’ll be too low for good seeing — or much after Mars crosses your local meridian, because you’d be viewing in the daytime.

Longitude of central meridian of Mars = 290 degrees;
Syrtis Major and Hellas transiting central meridian.

Tuesday      June  5   2:26 a.m. CDT
Wednesday June  6   3:04 a.m.
Thursday     June  7   3:43 a.m
Friday          June  8   4:21 a.m.
Saturday      June  9   4:59 a.m.
Sunday       June 10   5:38 a.m. (near sunrise, but observe earlier,
as these features approach the central meridian)

Monday    June 11   6:16 a.m.  ” ”
Tuesday   June 12   6:54 a.m.  ” ”



2018, June 1: Jupiter Shines From Southeast

Bright Jupiter, complimenting Venus in the western evening sky, shines from the south-southeastern sky this evening.  Now well past its opposition, Jupiter is passing Zubenelgenubi, in Libra.  Watch as Jupiter passes and moves away from the star.

For more about the bright evening planets, see these articles:

2018, June 1: Venus Gleams in West

Brilliant Venus shines from the western sky this evening. Tonight it reaches its maximum setting interval after sunset. — 2 hours, 40 minutes — for this evening appearance.  Watch Venus this month pass the Gemini Twins and move past the Beehive star cluster.

For more about the bright evening planets, see these articles:

2018, May 4: Venus and Jupiter in Evening Sky

Brilliant Venus shines from the western sky this evening.  On a day that started windy with rapidly moving clouds, winds from the northwest prevailed and brought in classical May evening skies to the Chicago area.

Venus appears in the western sky throughout the spring and summer.

Meanwhile in the eastern sky, Jupiter appears near the horizon.  Just a few days before its opposition, when it rises at sunset, Jupiter appears low in the sky.  Jupiter’s opposition begins a 79-day interval where three bright outer planets — Mars, Jupiter, and Saturn — appear close to Earth and bright in our sky.

For more about the bright evening planets, see these articles:

2018, April 25: Venus and Sirius

Brilliant Venus shines from the west-northwest this evening.  It is now setting over 2 hours after sunset.  After you locate Venus look to the left along the horizon.  Sirius, the brightest star, is in the southwest, at about the same altitude (height above the horizon) as Venus. They will be at about the same altitude for the next several days. Compare their respective brightness: Venus the brightest planet and Sirius the brightest star.  Venus is about 10 times brighter than Sirius.

For more about the bright evening planets, see these articles:

2018, April 10: The Morning Planets and the Moon

Less than a month before its opposition, Jupiter gleams from the southwest this morning. The planet is now rising in the east-southeast at about 10 p.m. Jupiter is retrograding near the star Zubenelgenubi.

Mars and Saturn are farther east, beyond the star Antares. Saturn rises before 2 a.m. with Mars following closely behind. Saturn’s opposition is in June. Mars’ opposition is July, three oppositions in 79 days.

This morning Mars and Saturn are about 4 degrees apart.  Saturn begins to retrograde in a week (April 17).

The waning crescent moon (24 days old) is low in the east-southeast this morning, outside the frame of the planets.

The articles that follow provide details about the planets visible without optical assistance (binoculars or telescope):

2018, April: Watch Venus Move Through Taurus

During late April, brilliant Venus moves through the stellar background of Taurus with its two bright star clusters:  Pleiades and Hyades.

On April 24, Venus is closest to Alcyone, the brightest star in the Pleiades cluster.  They are 3.5 degrees apart.

The Pleiades is a compact grouping of bright bluish stars known to school children as “The Seven Sisters.”  The cluster resembles a tiny dipper.  To the unaided eye, 6 or 7 stars are visible.  A dozen or so through binoculars.  A few hundred through telescopes.  The Hyades are nearby.  This group resembles a check mark, a letter “V” when Aldebaran is included, although it is not part of the cluster.

Astronomical theory describes that stars are formed in bunches from a stellar, gaseous nebula.  Over time the mutual gravitation pull of the stars within the cluster is not strong enough to keep the group together.  The Hyades and Pleaides are close enough (within 400 light years) that they can be seen without a telescope.  Many star clusters are just beyond the perception of our eyes.

The star cluster pair is best-observed through binoculars,  Start observing Venus’ movement through the region nightly at mid-month.  On April 18, the crescent moon appears among the Hyades.

Watch the events unfold during the spring evenings.

For more about Venus and the bright evening planets, see these articles: