Northern Hemisphere gazer's guide
July 4: The moon is at perigee, the position in its orbit where it is nearest Earth. July 5: Earth is at aphelion, the position in its elliptical orbit where its distance from the sun is greatest. The distance from Earth to the sun today is about 152.1 million kilometers (94.51 million miles). This is about 1.5 percent farther away than the average distance, about 3 percent farther away than the closest approach to the sun, on Jan. 3. Note that Earth is farthest from the sun in July, when it is summer in Northern Hemisphere, and closest when the hemisphere is beginning its winter. The seasons are not related in any way to Earth's distance from the sun, although the seasonal weather is affected by that distance. Northern summers and winters, severe as they may seem to be at times, are moderated by the effects of Earth's changing distance from the sun. Southern Hemisphere seasons, however, whereby Earth is nearest the sun in summer and farthest in winter, are made more extreme by the same factor.
July 6: Venus is already a prominet morning star, even though it went through inferior conjunction with the sun only three weeks ago. Today it ends its retrograde (westerly) motion through the starts and begins to follow the sun easterly once again, but more slowly. It will be separating to the sun's right until late in August, rising progressively earlier each morning and moving higher before it fades in the dawn.
July 9: At dawn this morning the waning crescent moon is between Aldebaran, the bright orange star in Taurus, and Venus, and a pretty sight it will be. In passing the star and the planet today, the moon covers both. The occultation of Aldebaran occurs shortly after midnight, before it rises in North America. But the occulation of Venus will occur over most of the United States except the Northeast and North Central states. Though it will be a daytime event, Venus is so bright that it should be visible in small telescopes, even binoculars. the time of the event will vary somewhat with location, but if you center the moon in the field from about 1:30 p.m. Eastern standard time on, you should see it. Don't forget to adjust for daylight time and for different time zones.
July 11: Mercury is in inferior conjunction and becomes a morning star.
July 15: The waxing crescent moon is between Regulus and Jupiter this evening , with Regulus to its right and Jupiter to its left, almost a repeat of its performance with Aldebaran and Venus of a week ago. And again the moon occults (covers) both objects, Regulus early this morning, Jupiter after dark. The occultation of Regulus occurs below our horizon, but Jupiter and the moon will still be above the horizon as the moon approaches the planet, covering it at about 10:30 p.m. EST. Even though they will set in Eastern, Central, and Mountain regions before the occultation, observers will be able to see the moon draw slowly closer to Jupiter from dusk until moonset. Again, a very pretty view, this one in the evening sky.
July 16: The crescent moon is between Jupiter (to its right) and Saturn (to its left and closer) tonight. It passes Saturn about 2 a.m. EST on the 17th, after both have set, also covering this planet (over the Pacific and Asia).
July 17: Tonight the crescent moon is between Saturn (to its right) and Mars (to its left). Mars has now dimmed substantially from its brightness of last February, and is now little brighter than Saturn. As you watch during the evening, you will see the moon pull away from Saturn and move toward Mars, passing the reddish planet at some distance at about 11 p.m. EST.
July 18: The moon is at apogee, farthest from Earth.
July 21: Venus reaches greatest brilliancy as a morning star. Although the planet continues to turn more of its sunlit face toward Earth, it is now moving rapidly away from us, causing it to dim slowly as its crescent shape waxes but grows smaller.
July 22: Having passed between Earth and sun (inferior conjunction), Mercury now ends its retrogate (westerly) motion through the stars and begins to move easterly once again.
July 27: A penumbral eclipse of the moon occurs today, not visible from North America. During a penumbral eclipse, part of the sun is obscured from the moon's surface by Earth, causing the moon to darken somewhat, but barely noticeably.
July 28: The delta Aquarid meteor shower reaches maximum this morning, producing up to about 20 shower meteors per hour, about half as many for two days before and after maximum.
July 30: The moon is at perigee, again at the position in its orbit where it is nearest Earth. The last perigee was on July 4, only a little more than 26 years ago.
July 31: Mercury is at its greatest distance to the right (west) of the sun (greatest westerly elongation). For about a week before this date, you may see the planet low in the east just after dawn.