By Alain Dussault
The Moon, the Sun, Spring and Summer Constellations
To begin with here are some more interesting sites on the Moon.
On the History or evolution of Moon maps`:
On evolution of Moon drawings:
On the Moon almanac:
A very interesting DOS program, which show all reliefs of the Moon maps, based on photography of the Moon, and also many information concerning the Moon. The program is in Italian, but its worth the detour, "MOON203.ZIP" (1 of 7).
Another program is MOONRIS3.ZIP. Use the search engine on the following to get it:
To obtain another Moon map visibility and a lot of details on it:
The Moon, our neighbour in space, has a diameter of 3,476 km (2,160m), that is a quarter the diameter of the Earth. The Moon take 27day, 7hr, 43min, 12sec to complete an orbit around the Earth. This time interval is named the sidereal period. It is the time that the Moon take to accomplish an orbit in comparison with the background stars. But the Moon take a little bit more time to complete its phase cycle. It needs then 2.25 more days to repeat over its phase cycle. This time interval requires of 29day, 12hr, 44min, 3sec, is named the synodic period.
It often happen that the Moon seem bigger when it rise than went it set. This is only an optical illusion. Finally, because the Moon is always near the ecliptic and the Full Moon is always opposed to the Sun, Full Moon is high in the Winter sky, and low in Summer sky.
The Moon is the easiest object in the sky to observe. It is very interesting to follow its phase cycle form the New Moon to the Full Moon.
The best location to look at to observe the Moon, because details are more evident, is at the Terminator, that is the place on the face of the Moon that separated the light part of it from the one which is dark.
To be able to observe the first Moon crescent, you must be out early at night, because the Moon is very low on the horizon and set rapidly. The more the Moon phase progress, the more the Moon rise late.
You can see many different types of reliefs as seas (Maria), oceans (Oceanus), lakes (Lacus), bays (Sinus), great crates, faults and mountains.
The observation of the Full Moon or at a phase near it, allow us to see special characteristics, that is ray craters.
You know that the surface of the Moon, present many scars, as craters,
which are the by effect of meteorites impact. The most recent impacts,
like the that create crater Tycho, have projected, on the Moon, ejection
matters all around it, which appear to us now like rays.
The Sun is a very brilliant star, to be able to observe it, we must used special filters, which cut 99% of the light of the Sun.
A virtual tour of the sun at: http://www.astro.uva.nl/michielb/od95/
We should never look at the Sun with naked eyes.
These special filters are sold as eye glasses in cardboard, which you can get at astronomy store for around 3.00$.
There is also special filters for binoculars and telescopes, but they are expansive. For example for an 8 inches telescope, a filter to place at the front of it, cost around 150$.
You should never used filters that screw at the back of eyepieces. Because when we allow all the light coming from the Sun to enter and pass through all optical parts of the telescope, these elements risk to overheat. so a filter screw at the back of an eyepiece can crack.
With special glasses to observe the Sun, they are not sunglasses, it is possible to observe big Sun spots. The Sun cycle has a duration of 11 years between minimum and maximum of spot activities.
But before using them, we must make sure that they are not damaged,they are no holes in the filters or cracks.
Bootes is a constellation that look like a kite. It is locate to the right of Hercules constellation and under Draco.
Near Bootes there are the globular clusters M3 of magnitude 6.4 and M53 of magnitude 7.7. Two objects not easy to locate with binoculars. In Bootes there is the fourth most brilliant star of our sky, that is Arcturus.
Leo is an easy constellation to identify, because of a group of stars that form a characteristic sickle or if you prefer an inverse interrogation point.
If you extend, in the south direction, the line that rely the stars Dubhe and Merak of Ursa Major, they will lead you to the Leo constellation. The most brilliant star of Leo is Regulus. Many nebulas make part of Leo, like the Messier objects M65, M66, and M95. There is also the spiral galaxy M96. Objects not easy for binoculars.
This constellation is located under the posterior feet of Ursa Major and just above the sickle of Leo. There is no object for binoculars there.
VIrgo is found in prolonging an imaginary line that pass by the tail of Ursa Major and the star Arcturus of Bootes. If we prolong this line toward the South, we arrive at the star Spica. Two Messier objects are in that constellation, that is M49 and M61.
Cygnus is a very interesting constellation to look at with binoculars, because it is locate in the Milky Way. To sweep through with binoculars is something. Anyway, sweeping through the sky following the MIlky Way is very rewarding.
In Cygnus, three objects merit a look at. It is the Messier objects, M39 and M29, which are open clusters. These objects are easy to locate. Then there is the famous double star named Albireo, which is the tail star of the cross form of the constellation. One the star is yellow and the other is blue.
Visual color of a star reveal its surface temperature or its age. A blue star is more cold and younger than a yellow star. A red star is older and more warm.
Lyra is a small constellation, which is easily located by its bluish star Vega. This star is the most brilliant star of the summer sky.
In this constellation, there is the famous Ring nebula, Messier M57. A nebula which look like a doughnut. You will find there also the globular cluster M56. both of these objects are not easy for binoculars.
Aquila is a small equatorial constellation. In it, find the star Altair. The stars Altair, Vega and Deneb form the famous summer triangle.
In a zone south of Cygnus, we find the constellation Vulpecula. This constellation is not much important. In it there is the famous Dumbell nebula, Messier object M27.
Between Cygnus and Andromeda, is locate Lacerta. No brilliant stars there and no Messier object.
Sagitta a small constellation which look like an arrow, is found south
of Cygnus. It is locate in the Milky Way region and contain the globular
Hercules is very easy to find in the sky, by its inverse trapeze form. In it there is two Messier objects, which are globular clusters. The most famous is M13, a blob in binoculars, but also visible to the naked eyes for certain persons. the other is Messier M92. Smaller than M13 and also more difficult to find.
Between Hercules and Bootes, we find Corona borealis. This is a small constellation which has a distinct form like a tiara.
Next chapter, The Planets (Jupiter, Mars, Venus, Saturne and Mercury)
Preceding chapter, The References to help in observing (Maps, softwares, Internet)
Return to the main page, Introduction
Last update February 5th., 1998.