But here we come up against the most difficult of all obstacles to contact with people on other planets -- the astronomical distances which separate us.

come up against ^{if you come up against a problem or difficulty, you are faced with it and have to deal with it 遇到/遭遇;面临（问题、困难）}

• We may find we come up against quite a lot of opposition from local people.
• We came up against a great deal of resistance in dealing with the case.
• The construction project suddenly came up against unexpected legal issues.^{该建设项目突然遭遇了意料之外的法律问题。}
• We must be prepared to come up against stiff competition in the international market.^{我们必须准备好在国际市场上遭遇激烈的竞争。}

the most difficult of all obstacles ^{所有障碍中最困难的}

• That is perhaps why sculpture has been described as the most difficult of all arts; certainly it is more difficult than the arts which involve appreciation of flat forms, shape in only two dimensions.
• Lack of consistent funding is the most difficult of all obstacles facing the research team.^{缺乏持续的资金是研究团队面临的所有障碍中最困难的。}
• the most difficult of all arts ↔ the most difficult art of all
• the most difficult of all obstacles ↔ the most difficult obstacle of all
• the greatest of all Western stars ↔ the greatest Western star of all
• the most valuable find of all ↔ the most valuable of all finds
• the most frightening thing of all ↔ the most frightening of all things
• the deepest holes of all ↔ the deepest of all holes 

obstacle to sth. ^{…的障碍；阻碍…的东西( 介词to而非to do不定式 )}

• obstacles to world peace
• This decision has removed the last obstacle to the hostages' release.
• The agreement removes the last serious obstacle to the signing of the arms treaty. ^{该协议为武器条约的签署去除了最后一个重大障碍。}

contact with ^{n. 联系；接触(名词需要与 with 搭配)}

• The children lost contact with their families.
• Please do not hesitate to contact me if you have any queries. ^{vt.联系（动词及物，无需 with）}
• She has been in regular contact with her colleagues via email while working from home. ^{居家办公期间，她一直通过电子邮件与同事保持定期联系。}

As a reasonable guess, they might, on an average, be 100 light years away. (A light year is the distance which light travels at 186,000 miles per second in one year, namely 6 million million miles.)

on (an) average ^平均来说

• On average, men still earn more than women.
• On an average, women live between five and seven years longer than men. 
• On an average, our employees commute for thirty minutes each way.^{平均来说，我们的员工单程通勤三十分钟。}

namely ^{adv. that is to say 即/也就是}

• Only one boy was absent, namely Harry.
• We need to concentrate on our target audience, namely women aged between 20 and 30.
• The main objective of the mission, namely finding extraterrestrial life, is highly ambitious.^{这次任务的主要目标，即寻找地外生命，雄心勃勃。}

Radio waves also travel at the speed of light, and assuming such an automatic messenger picked up our first broadcasts of the 1920's, the message to its home planet is barely halfway there.

 assuming (that) … ^{conj. 1、假定，假如}

• Assuming (that) the house is for sale, would you buy it?
• You can stretch your legs on the spacious decks, play games, swim, meet interesting people and enjoy good food―always assuming, of course, that the sea is calm.
• Assuming all goes according to plan, the construction should be finished by next month.^{假设一切都按计划进行，施工应该在下个月完成。}

assuming (that) … ^{conj. 2、以为}

• Assuming (that) the man was making a homosexual advance, he stormed out of the  house angrily.
• Assuming that his family had been killed during an air-raid, Hans settled down in a Village fifty miles away where he had remained ever since.

pick sth. up  ^{(of a piece of electrical equipment) to receive a signal 接收信号}

• The equipment picked up the signal from the satellite.
• We were able to pick up the BBC World Service.
• We can pick up Mexican television. ^{我们可以接收到墨西哥电视。}

Similarly, our own present primitive chemical rockets, though good enough to orbit men, have no chance of transporting us to the nearest other star, four light years away, let alone distances of tens or hundreds of light years.

similarly ^{adv.  类似地，同样地}

• The cost of food and clothing has come down in recent years. Similarly, fuel prices have fallen quite considerably.
• High inflation usually leads to high interest rates. Similarly, interest rates decline when inflation is low.
• The first experiment yielded positive results; similarly, the second trial showed significant improvement. ^{第一个实验取得了积极的结果；同样地，第二次试验也显示出显著的改善。}

orbit ^{v. 1. to revolve in an orbit around 绕…的轨道运行}

• The earth takes a year to orbit the sun.
• Once the Soyuz began to orbit the Earth, the failures began. ^{当联盟号开始环绕地球的时候，失败随之降临了。}
•  The Moon's rotation rate, and the time it takes to orbit Earth are the same. ^{月球的自转速度与绕地球公转速度是一样的。}

orbit ^{v. 2. to send up and make revolve in an orbit 把…送入轨道；使绕轨道运行}

• It takes a massive amount of fuel and precision to orbit a satellite around the Earth. ^{将卫星送入地球轨道并使其运行需要大量的燃料和极高的精度。}
• The aerospace company successfully orbited several small communications satellites last month. ^{这家航空航天公司上个月成功地将几颗小型通讯卫星送入了轨道。}

chance ^{n. [C & U] possibility 可能性}

• She has a good chance of a successful recovery.
• Is there any chance of getting tickets for tonight's performance?
• Perhaps it is the desire for solitude or the chance of making an unexpected discovery that lures men down to the depths of the earth.
• There is a slight chance that it will rain this afternoon, so you might want to bring an umbrella. ^{今天下午有一点点下雨的可能，所以你可能想带把伞。}

let alone = much less / still less ^{用在否定句后，表2个都没戏，都不可能}

• The baby can’t talk, let alone run.
• He can’t run a hundred yards, let alone a mile.
• I don’t suspect him of theft, let alone of robbery.
• Tony can barely boil an egg, much less cook dinner.